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A. P. J. Jansen

A.P.J. Jansen

Jansen A. P. J.

Island formation without attractive interactions

11 pages, 4 figures

10.1103/PhysRevB.77.073408

cond-mat.stat-mech cond-mat.mtrl-sci

We show that adsorbates on surfaces can form islands even if there are no attractive interactions. Instead strong repulsion between adsorbates at short distances can lead to islands, because such islands increase the entropy of the adsorbates that are not part of the islands. We suggest that this mechanism cause the observed island formation in O/Pt(111), but it may be important for many other systems as well.

v1 (Mon, 18 Feb 2008 15:15:49 GMT)

Dominic Horsman

Dominic Horsman

Horsman Dominic

An introduction to many worlds in quantum computation

Published version. This supercedes quant-ph/0210204. Comments welcome

Found. Phys. 39(8) August 2009

10.1007/s10701-009-9300-2

quant-ph

The interpretation of quantum mechanics is an area of increasing interest to many working physicists. In particular, interest has come from those involved in quantum computing and information theory, as there has always been a strong foundational element in this field. This paper introduces one interpretation of quantum mechanics, a modern `many-worlds' theory, from the perspective of quantum computation. Reasons for seeking to interpret quantum mechanics are discussed, then the specific `neo-Everettian' theory is introduced and its claim as the best available interpretation defended. The main objections to the interpretation, including the so-called ``problem of probability'' are shown to fail. The local nature of the interpretation is demonstrated, and the implications of this both for the interpretation and for quantum mechanics more generally are discussed. Finally, the consequences of the theory for quantum computation are investigated, and common objections to using many worlds to describe quantum computing are answered. We find that using this particular many-worlds theory as a physical foundation for quantum computation gives several distinct advantages over other interpretations, and over not interpreting quantum theory at all.

v1 (Mon, 18 Feb 2008 15:24:47 GMT), v2 (Wed, 8 Jul 2009 08:34:32 GMT)

Roberto D. Mota Esteves

D. Martinez, V. D. Granados and R. D. Mota

Martinez D., Granados V. D., Mota R. D.

SU(2) Symmetry and Degeneracy From SUSY QM of a Neutron in the Magnetic Field of a Linear Current

Phys.Lett.A350:31-35,2006

10.1016/j.physleta.2005.10.001

quant-ph

From SUSY ladder operators in momentum space of a neutron in the magnetic field of a linear current, we construct $2\times 2$ matrix operators that together with the z-component of the angular momentum satisfy the su(2) Lie algebra. We use this fact to explain the degeneracy of the energy spectrum.

v1 (Mon, 18 Feb 2008 15:25:41 GMT)

Larry Bradley

L. D. Bradley, R. J. Bouwens, H. C. Ford, G. D. Illingworth, M. J. Jee, N. Benitez, T. J. Broadhurst, M. Franx, B. L. Frye, L. Infante, V. Motta, P. Rosati, R. L. White, W. Zheng

Bradley L. D., Bouwens R. J., Ford H. C., Illingworth G. D., Jee M. J., Benitez N., Broadhurst T. J., Franx M., Frye B. L., Infante L., Motta V., Rosati P., White R. L., Zheng W.

Discovery of a Very Bright Strongly-Lensed Galaxy Candidate at z ~ 7.6

Accepted for publication in the Astrophysical Journal, 8 pages, 8 figures, updated to match version in press

10.1086/533519

astro-ph

Using HST and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z~7.6 in the field of the massive galaxy cluster Abell 1689. The galaxy candidate, which we refer to as A1689-zD1, shows a strong z-J break of at least 2.2 mag and is completely undetected (<1 sigma) in HST/ACS g, r, i, and z-band data. These properties, combined with the very blue J-H and H-[4.5] colors, are exactly the properties of an z~7.6 LBG and can only be reasonably fit by a star-forming galaxy at z=7.6 +/- 0.4. Attempts to reproduce these properties with a model galaxy at z<4 yield particularly poor fits. A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H band and is ~1.3 mag brighter than the brightest-known z-dropout galaxy. When corrected for the cluster magnification of 9.3 at z~7.6, the candidate has an intrinsic magnitude of H=27.1 AB, or about an L* galaxy at z~7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size ~<300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9) x 10^9 M_sun, stellar ages 45-320 Myr, star-formation rates ~<7.6 M_sun/yr, and low reddening with A_V <= 0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t~<0.63 Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.

v1 (Mon, 18 Feb 2008 20:48:20 GMT), v2 (Tue, 13 May 2008 19:15:14 GMT)

George Palasantzas

G. Palasantzas

Palasantzas G.

Surface roughness influence on the quality factor of high frequency nanoresonators

13 pages, 4 figures, To appear in J. Appl. Phys. (2008)

10.1063/1.2874790

physics.flu-dyn

Surface roughness influences significantly the quality factor of high frequency nanoresonators for large frequency - relaxation times within the non-Newtonian regime, where a purely elastic dynamics develops. It is shown that the influence of sort wavelength roughness, which is expressed by the roughness exponent H for the case of self-affine roughness, plays significant role in comparison with the effect of the long wavelength roughness parameters such as the rms roughness amplitude and the lateral roughness correlation length. Therefore, the surface morphology can play important role in designing high-frequency resonators operating within the non-Newtonian regime.

v1 (Mon, 18 Feb 2008 15:32:51 GMT)

Marcus Kaiser

Marcus Kaiser, Matthias Goerner and Claus C. Hilgetag

Kaiser Marcus, Goerner Matthias, Hilgetag Claus C.

Criticality of spreading dynamics in hierarchical cluster networks without inhibition

New Journal of Physics, 9:110 (2007)

10.1088/1367-2630/9/5/110

q-bio.NC physics.soc-ph q-bio.PE

An essential requirement for the representation of functional patterns in complex neural networks, such as the mammalian cerebral cortex, is the existence of stable network activations within a limited critical range. In this range, the activity of neural populations in the network persists between the extremes of quickly dying out, or activating the whole network. The nerve fiber network of the mammalian cerebral cortex possesses a modular organization extending across several levels of organization. Using a basic spreading model without inhibition, we investigated how functional activations of nodes propagate through such a hierarchically clustered network. The simulations demonstrated that persistent and scalable activation could be produced in clustered networks, but not in random networks of the same size. Moreover, the parameter range yielding critical activations was substantially larger in hierarchical cluster networks than in small-world networks of the same size. These findings indicate that a hierarchical cluster architecture may provide the structural basis for the stable and diverse functional patterns observed in cortical networks.

v1 (Mon, 18 Feb 2008 16:23:22 GMT)

Ilaria Biscardi

I. Biscardi (1,2), G. Raimondo (1), M. Cantiello (1,3) and E. Brocato (1) ((1) INAF-Osservatorio Astronomico di Teramo, (2) Dipartimento di Fisica - Universita' di Roma Tor Vergata, (3) Department of Physics and Astronomy, Washington State University, Pullman, USA)

Biscardi I., Raimondo G., Cantiello M., Brocato E.

Optical Surface Brightness Fluctuations of shell galaxies towards 100 Mpc

29 pages, 7 figures, 5 tables. Accepted for Publication in ApJ

10.1086/587126

astro-ph

We measure F814W Surface Brightness Fluctuations (SBF) for a sample of distant shell galaxies with radial velocities ranging from 4000 to 8000 km/s. The distance at galaxies is then evaluated by using the SBF method. For this purpose, theoretical SBF magnitudes for the ACS@HST filters are computed for single burst stellar populations covering a wide range of ages (t=1.5-14 Gyr) and metallicities (Z=0.008-0.04). Using these stellar population models we provide the first $\bar{M}_{F814W}$ versus $(F475W-F814W)_0$ calibration and we extend the previous I-band versus $(B-I)_0$ color relation to colors $(B-I)_{0}\leq 2.0$ mag. Coupling our SBF measurements with the theoretical calibration we derive distances with a statistical uncertainty of $\sim 8%$, and systematic error of $\sim 6 %$. The procedure developed to analyze data ensures that the indetermination due to possible unmasked residual shells is well below $\sim 12 %$. The results suggest that \emph{optical} SBFs can be measured at $d \geq 100 Mpc$ with ACS@HST imaging. SBF-based distances coupled with recession velocities corrected for peculiar motion, allow us obtain $H_{0} = 76 \pm 6$ (statistical) $\pm 5$ (systematic) km/s/Mpc.

v1 (Mon, 18 Feb 2008 16:20:45 GMT)

Paramita Dey

Paramita Dey, Anirban Kundu, Biswarup Mukhopadhyaya

Dey Paramita, Kundu Anirban, Mukhopadhyaya Biswarup

Some consequences of a Higgs triplet

Revised version, 25 pages, 4 figures

J.Phys.G36:025002,2009

10.1088/0954-3899/36/2/025002

hep-ph

We consider an extension of the scalar sector of the Standard Model with a single complex Higgs triplet $X$. Such extensions are the most economic, model-independent way of generating neutrino masses through triplet interactions. We show that a term like $\azero\Phi\Phi X^\dag$ must be included in the most general potential of such a scenario, in order to avoid a massless neutral physical scalar. We also demonstrate that $\azero$ must be real, thus ruling out any additional source of CP-violation. We then examine the implications of this term in the mass matrices of the singly-and doubly-charged scalar, neutral scalar and pseudoscalar fields. We find that, for small values of $\azero/\vtwo$, where $\vtwo$ is the triplet vev, the spectrum allows the decay of heavier scalars into lighter ones via gauge interactions. For large $\azero/\vtwo$, the doubly-charged, singly-charged and neutral pseudoscalar bosons become practically degenerate, while the even-parity neutral scalars remain considerably lighter, thus emphasizing the possibility of decay of the singly-charged or neutral pseudoscalar states into the neutral scalars. Constraints from the $\rho$-parameter are used to find nontrivial limits on the charged Higgs mass depending on $\azero$. We also study the couplings of the various physical states in this scenario. For small values of $|\azero|/\vtwo$, we find the lightest neutral scalar field to be triplet-dominated, and thus having extremely suppressed interactions with fermion as well as gauge boson pairs.

v1 (Mon, 18 Feb 2008 16:24:55 GMT), v2 (Tue, 30 Dec 2008 12:30:19 GMT)

Marcus Kaiser

Florian Nisbach and Marcus Kaiser

Nisbach Florian, Kaiser Marcus

Developmental time windows for spatial growth generate multiple-cluster small-world networks

Eur. Phys. J. B 58, 185-191 (2007)

10.1140/epjb/e2007-00214-4

physics.soc-ph q-bio.NC

Many networks extent in space, may it be metric (e.g. geographic) or non-metric (ordinal). Spatial network growth, which depends on the distance between nodes, can generate a wide range of topologies from small-world to linear scale-free networks. However, networks often lacked multiple clusters or communities. Multiple clusters can be generated, however, if there are time windows during development. Time windows ensure that regions of the network develop connections at different points in time. This novel approach could generate small-world but not scale-free networks. The resulting topology depended critically on the overlap of time windows as well as on the position of pioneer nodes.

v1 (Mon, 18 Feb 2008 16:30:19 GMT)

Marcus Kaiser

Marcus Kaiser

Kaiser Marcus

Mean clustering coefficients: the role of isolated nodes and leafs on clustering measures for small-world networks

final version of the manuscript

Marcus Kaiser 2008 New J. Phys. 10 083042

10.1088/1367-2630/10/8/083042

physics.soc-ph q-bio.MN

Many networks exhibit the small-world property of the neighborhood connectivity being higher than in comparable random networks. However, the standard measure of local neighborhood clustering is typically not defined if a node has one or no neighbors. In such cases, local clustering has traditionally been set to zero and this value influenced the global clustering coefficient. Such a procedure leads to underestimation of the neighborhood clustering in sparse networks. We propose to include $\theta$ as the proportion of leafs and isolated nodes to estimate the contribution of these cases and provide a formula for estimating a clustering coefficient excluding these cases from the Watts and Strogatz (1998 Nature 393 440-2) definition of the clustering coefficient. Excluding leafs and isolated nodes leads to values which are up to 140% higher than the traditional values for the observed networks indicating that neighborhood connectivity is normally underestimated. We find that the definition of the clustering coefficient has a major effect when comparing different networks. For metabolic networks of 43 organisms, relations changed for 58% of the comparisons when a different definition was applied. We also show that the definition influences small-world features and that the classification can change from non-small-world to small-world network. We discuss the use of an alternative measure, disconnectedness D, which is less influenced by leafs and isolated nodes.

v1 (Mon, 18 Feb 2008 16:47:38 GMT), v2 (Sun, 16 Mar 2008 20:01:35 GMT), v3 (Fri, 29 Aug 2008 17:42:24 GMT)

Joachim Kopp

Evgeny Kh. Akhmedov, Joachim Kopp, Manfred Lindner

Akhmedov Evgeny Kh., Kopp Joachim, Lindner Manfred

Oscillations of Mossbauer neutrinos

31 pages, 2 figures, RevTeX4, minor clarifications in the text, matches version to be published in JHEP

JHEP0805:005,2008

10.1088/1126-6708/2008/05/005

hep-ph hep-ex nucl-th

We calculate the probability of recoilless emission and detection of neutrinos (Mossbauer effect with neutrinos) taking into account the boundedness of the parent and daughter nuclei in the neutrino source and detector as well as the leptonic mixing. We show that, in spite of their near monochromaticity, the recoillessly emitted and captured neutrinos oscillate. After a qualitative discussion of this issue, we corroborate and extend our results by computing the combined rate of $\bar{\nu}_e$ production, propagation and detection in the framework of quantum field theory, starting from first principles. This allows us to avoid making any a priori assumptions about the energy and momentum of the intermediate-state neutrino. Our calculation permits quantitative predictions of the transition rate in future experiments, and shows that the decoherence and delocalization factors, which could in principle suppress neutrino oscillations, are irrelevant under realistic experimental conditions.

v1 (Mon, 18 Feb 2008 17:09:14 GMT), v2 (Fri, 2 May 2008 09:43:30 GMT)

Kathrin Wimmer

K. Wimmer, V. Bildstein, K. Eppinger, R. Gernh\"auser, D. Habs, Ch. Hinke, Th. Kr\"oll, R. Kr\"ucken, R. Lutter, H.-J. Maier, P. Maierbeck, Th. Morgan, O. Schaile, W. Schwerdtfeger, S. Schwertel and P.G. Thirolf

Wimmer K., Bildstein V., Eppinger K., Gernhäuser R., Habs D., Hinke Ch., Kröll Th., Krücken R., Lutter R., Maier H. -J., Maierbeck P., Morgan Th., Schaile O., Schwerdtfeger W., Schwertel S., Thirolf P. G.

First identification of large electric monopole strength in well-deformed rare earth nuclei

submitted to Physics Letters B

10.1063/1.3087080

nucl-ex

Excited states in the well-deformed rare earth isotopes $^{154}$Sm and $^{166}$Er were populated via ``safe'' Coulomb excitation at the Munich MLL Tandem accelerator. Conversion electrons were registered in a cooled Si(Li) detector in conjunction with a magnetic transport and filter system, the Mini-Orange spectrometer. For the first excited $0^+$ state in $^{154}$Sm at 1099 keV a large value of the monopole strength for the transition to the ground state of $\rho^2(\text{E0}; 0^+_2 \to 0^+_\text{g}) = 96(42)\cdot 10^{-3}$ could be extracted. This confirms the interpretation of the lowest excited $0^+$ state in $^{154}$Sm as the collective $\beta$-vibrational excitation of the ground state. In $^{166}$Er the measured large electric monopole strength of $\rho^2(\text{E0}; 0^+_4 \to 0^+_1) = 127(60)\cdot 10^{-3}$ clearly identifies the $0_4^+$ state at 1934 keV to be the $\beta$-vibrational excitation of the ground state.

v1 (Mon, 18 Feb 2008 16:58:19 GMT)

Roberto Decarli

R.Decarli, R.Falomo, J.Kotilainen, M.Labita, R.Scarpa, A.Treves

Decarli R., Falomo R., Kotilainen J., Labita M., Scarpa R., Treves A.

Re-classification of the alleged quasar Q0045-3337

Accepted for publication in the Bentham Open Astronomy Journal

Bentham Open Astronomy Journal, 2009, 2

10.2174/1874381100902010023

astro-ph

We present a medium-resolution optical spectrum of the alleged high-redshift quasar Q0045-3337, taken at the ESO/3.6m telescope. Our observations show that the object is not a quasar but a star of spectral type B. We suggest that the object is either a white dwarf or a halo population Blue Horizontal Branch star.

v1 (Mon, 18 Feb 2008 16:58:30 GMT), v2 (Tue, 24 Mar 2009 13:55:07 GMT)

Stefan Kurth

E. Khosravi, S. Kurth, G. Stefanucci, E.K.U. Gross

Khosravi E., Kurth S., Stefanucci G., Gross E. K. U.

The Role of Bound States in Time-Dependent Quantum Transport

10 pages, 8 figures

10.1007/s00339-008-4864-9

cond-mat.mes-hall

Charge transport through a nanoscale junction coupled to two macroscopic electrodes is investigated for the situation when bound states are present. We provide numerical evidence that bound states give rise to persistent, non-decaying current oscillations in the junction. We also show that the amplitude of these oscillations can exhibit a strong dependence on the history of the applied potential as well as on the initial equilibrium configuration. Our simulations allow for a quantitative investigation of several transient features. We also discuss the existence of different time-scales and address their microscopic origin.

v1 (Mon, 18 Feb 2008 17:02:28 GMT)

Amos Ron

Ronald DeVore and Amos Ron

DeVore Ronald, Ron Amos

Approximation using scattered shifts of a multivariate function

math.CA math.FA

The approximation of a general $d$-variate function $f$ by the shifts $\phi(\cdot-\xi)$, $\xi\in\Xi\subset \Rd$, of a fixed function $\phi$ occurs in many applications such as data fitting, neural networks, and learning theory. When $\Xi=h\Z^d$ is a dilate of the integer lattice, there is a rather complete understanding of the approximation problem \cite{BDR,Johnson1} using Fourier techniques. However, in most applications the {\it center} set $\Xi$ is either given, or can be chosen with complete freedom. In both of these cases, the shift-invariant setting is too restrictive. This paper studies the approximation problem in the case $\Xi$ is arbitrary. It establishes approximation theorems whose error bounds reflect the local density of the points in $\Xi$. Two different settings are analyzed. The first is when the set $\Xi$ is prescribed in advance. In this case, the theorems of this paper show that, in analogy with the classical univariate spline approximation, improved approximation occurs in regions where the density is high. The second setting corresponds to the problem of non-linear approximation. In that setting the set $\Xi$ can be chosen using information about the target function $f$. We discuss how to `best' make these choices and give estimates for the approximation error.

v1 (Mon, 18 Feb 2008 18:52:55 GMT)

Anh-Thu Le

Van-Hoang Le, Ngoc-Ty Nguyen, C. Jin, Anh-Thu Le, C. D. Lin

Le Van-Hoang, Nguyen Ngoc-Ty, Jin C., Le Anh-Thu, Lin C. D.

Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra

14 pages, 9 figures

J. Phys. B: At. Mol. Opt. Phys. 41, 085603 (2008)

10.1088/0953-4075/41/8/085603

physics.atom-ph physics.optics

We illustrate an iterative method for retrieving the internuclear separations of N$_2$, O$_2$ and CO$_2$ molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible.

v1 (Mon, 18 Feb 2008 17:19:09 GMT)

Nikitas Papasimakis

N.I. Zheludev, S.L. Prosvirnin, N. Papasimakis and V.A. Fedotov

Zheludev N. I., Prosvirnin S. L., Papasimakis N., Fedotov V. A.

Coherent meta-materials and the lasing spaser

Nature Photonics 2, 351 - 354 (2008)

10.1038/nphoton.2008.82

physics.optics

In 2003 Bergman and Stockman introduced the spaser, a quantum amplifier of surface plasmons by stimulated emission of radiation [1]. They argued that, by exploiting a metal/dielectric composite medium, it should be possible to construct a nano-device, where a strong coherent field is built up in a spatial region much smaller than the wavelength [1,2]. V-shaped metallic inclusion, combined with a collection of semiconductor quantum dots were discussed as a possible realization of the spaser [1]. Here we introduce a further development of the spaser concept. We show that by combining the metamaterial and spaser ideas one can create a narrow-diversion coherent source of electromagnetic radiation that is fuelled by plasmonic oscillations. We argue that two-dimensional arrays of a certain class of plasmonic resonators supporting high-Q coherent current excitations provide an intriguing opportunity to create spatially and temporally coherent laser source, the Lasing Spaser.

v1 (Mon, 18 Feb 2008 17:37:34 GMT)

Pablo Laguna

M. C. Washik, J. Healy, F. Herrmann, I. Hinder, D. M. Shoemaker, P. Laguna, R. A. Matzner

Washik M. C., Healy J., Herrmann F., Hinder I., Shoemaker D. M., Laguna P., Matzner R. A.

Binary Black Hole Encounters, Gravitational Bursts and Maximum Final Spin

Replaced with version to appear in PRL

Phys.Rev.Lett.101:061102,2008

10.1103/PhysRevLett.101.061102

gr-qc astro-ph

The spin of the final black hole in the coalescence of nonspinning black holes is determined by the ``residual'' orbital angular momentum of the binary. This residual momentum consists of the orbital angular momentum that the binary is not able to shed in the process of merging. We study the angular momentum radiated, the spin of the final black hole and the gravitational bursts in a series of orbits ranging from almost direct infall to numerous orbits before infall that exhibit multiple bursts of radiation in the merger process. We show that the final black hole gets a maximum spin parameter $a/M_h \le 0.78$, and this maximum occurs for initial orbital angular momentum $L \approx M^2_h$.

v1 (Mon, 18 Feb 2008 17:24:58 GMT), v2 (Tue, 22 Jul 2008 14:38:59 GMT)

Fangwei Ye

Fangwei Ye, Yaroslav V. Kartashov, and Lluis Torner

Ye Fangwei, Kartashov Yaroslav V., Torner Lluis

Nonlocal surface dipoles and vortices

20 pages, 5 figures, to appear in Phys. Rev. A

Phys. Rev. A 77, 033829 (2008)

10.1103/PhysRevA.77.033829

nlin.PS nlin.SI physics.optics

We predict the existence and address the stability of two-dimensional surface solitons featuring topologically complex shapes, including dipoles, vortices, and bound states of vortex solitons, at the interface of nonlocal thermal media. Unlike their counterparts in bulk media, surface dipoles are found to be stable in the entire existence domain. Surface vortices are found to exhibit strongly asymmetric intensity and phase distributions, and are shown to be stable, too. Bound states of surface vortex solitons belong to a novel class of surface solitons having no counterparts in bulk media. Such states are found to be stable provided that their energy flow does not exceed an upper threshold. Our findings constitute the first known example of topologically complex solitons located at nonlocal two-dimensional interfaces.

v1 (Mon, 18 Feb 2008 17:28:48 GMT)

Marian Douspis

Alexandre Refregier and the DUNE collaboration

Refregier Alexandre, collaboration the DUNE

The Dark UNiverse Explorer (DUNE): Proposal to ESA's Cosmic Vision

Accepted in Experimental Astronomy

Exper.Astron.23:17-37,2009

10.1007/s10686-008-9106-9

astro-ph

The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary goal is the study of dark energy and dark matter with unprecedented precision. For this purpose, DUNE is optimised for the measurement of weak gravitational lensing but will also provide complementary measurements of baryonic accoustic oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate auxiliary goals concern the evolution of galaxies, to be studied with unequalled statistical power, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planets. DUNE is an Medium-class mission which makes use of readily available components, heritage from other missions, and synergy with ground based facilities to minimise cost and risks. The payload consists of a 1.2m telescope with a combined visible/NIR field-of-view of 1 deg^2. DUNE will carry out an all-sky survey, ranging from 550 to 1600nm, in one visible and three NIR bands which will form a unique legacy for astronomy. DUNE will yield major advances in a broad range of fields in astrophysics including fundamental cosmology, galaxy evolution, and extrasolar planet search. DUNE was recently selected by ESA as one of the mission concepts to be studied in its Cosmic Vision programme.

v1 (Mon, 18 Feb 2008 17:39:24 GMT), v2 (Wed, 28 May 2008 15:15:37 GMT), v3 (Thu, 29 May 2008 09:38:32 GMT), v4 (Thu, 24 Jul 2008 09:01:20 GMT)

Christian Corda

Christian Corda

Corda Christian

An oscillating Universe from the linearized R^{2} theory of gravity

To appear in General Relativity and Gravitation DOI: 10.1007/s10714-008-0627-3

Gen.Rel.Grav.40:2201-2212,2008

10.1007/s10714-008-0627-3

astro-ph

An oscillating Universe which arises from the linearized R^{2} theory of gravity is discussed, showing that some observative evidences like the cosmological redshift and the Hubble law are in agreement with the model. In this context Dark Energy is seen like a pure curvature effect arising by the Ricci scalar.

v1 (Mon, 18 Feb 2008 17:39:59 GMT), v2 (Tue, 19 Feb 2008 10:24:05 GMT)

Sergei Zharkov Dr

S.Zharkov, C.Nicholas, M.J.Thompson

Zharkov S., Nicholas C., Thompson M. J.

Time Distance Study of Isolated Sunspots

5 pages, 5 figures

Astron.Nachr.328:240-244, 2007

10.1002/asna.200610744

astro-ph

We present a comparative seismic study of conditions around and beneath isolated sunspots. Using the European Grid of Solar Observations' Solar Feature Catalogue of sunspots derived from SOHO/MDI continuum and magnetogram data, 1996-2005, we identify a set of isolated sunspots by checking that within a Carrington Rotation there were no other spots detected in the vicinity. We then use level-2 tracked MDI Dopplergrams available from SOHO website to investigate wave-speed perturbations of such sunspots using time-distance helioseismology.

v1 (Mon, 18 Feb 2008 18:01:22 GMT)

Pol Bernard Gossiaux

P.B. Gossiaux and J. Aichelin

Gossiaux P. B., Aichelin J.

Towards an understanding of the RHIC single electron data

Accepted for publication in Physical Review C

Phys.Rev.C78:014904,2008

10.1103/PhysRevC.78.014904

hep-ph

High transverse momentum ($p_T$) single non-photonic electrons which have been measured in the RHIC experiments come dominantly from heavy meson decay. The ratio of their $p_T$ spectra in pp and AA collisions ($R_{AA}(p_T)$) reveals the energy loss of heavy quarks in the environment created by AA collisions. Using a fixed coupling constant and the Debye mass ($m_D\approx gT$) as infrared regulator perturbative QCD (pQCD) calculations are not able to reproduce the data, neither the energy loss nor the azimuthal $(v_2)$ distribution. Employing a running coupling constant and replacing the Debye mass by a more realistic hard thermal loop (HTL) calculation we find a substantial increase of the collisional energy loss which brings the $v_2(p_T)$ distribution as well as $R_{AA}(p_T)$ to values close to the experimental ones without excluding a contribution from radiative energy loss.

v1 (Mon, 18 Feb 2008 18:08:27 GMT), v2 (Wed, 18 Jun 2008 09:50:06 GMT)

Paul Smolen

Paul Smolen, Douglas A. Baxter, John H. Byrne

Smolen Paul, Baxter Douglas A., Byrne John H.

Bistable MAP Kinase Activity: A Plausible Mechanism Contributing to Maintenance of Late Long-Term Potentiation

33 pages. 7 figures are at end

Am J Physiol Cell Physiol. 2008; v294, C503-C515

q-bio.MN q-bio.NC

Bistability of MAP kinase (MAPK) activity has been suggested to contribute to several cellular processes, including differentiation and long-term synaptic potentiation. A recent model (48) predicts bistability due to interactions of the kinases and phosphatases in the MAPK pathway, without feedback from MAPK to earlier reactions. Using this model and enzyme concentrations appropriate for neurons, we simulated bistable MAPK activity, but bistability only was present within a relatively narrow range of activity of Raf, the first pathway kinase. Stochastic fluctuations in molecule numbers eliminated bistability for small molecule numbers, such as are expected in the volume of a dendritic spine. However, positive feedback loops have been posited from MAPK up to Raf activation. One proposed loop in which MAPK directly activates Raf was incorporated into the model. We found that such feedback greatly enhanced the robustness of both stable states of MAPK activity to stochastic fluctuations and to parameter variations. Bistability was robust for molecule numbers plausible for a dendritic spine volume. The upper state of MAPK activity was resistant to inhibition of MEK activation for > 1 h, suggesting inhibitor experiments have not sufficed to rule out a role for persistent MAPK activity in LTP maintenance. These simulations suggest that persistent MAPK activity and consequent upregulation of translation may contribute to LTP maintenance and to long-term memory. Experiments using a fluorescent MAPK substrate may further test this hypothesis.

v1 (Mon, 18 Feb 2008 19:15:25 GMT)

Abhay Ashtekar

Abhay Ashtekar, Jonathan Engle and David Sloan

Ashtekar Abhay, Engle Jonathan, Sloan David

Asymptotics and Hamiltonians in a First order formalism

18 pages, No figures. Added a footnote 2 and two references

Class.Quant.Grav.25:095020,2008

10.1088/0264-9381/25/9/095020

gr-qc hep-th math-ph math.MP

We consider 4-dimensional space-times which are asymptotically flat at spatial infinity and show that, in the first order framework, action principle for general relativity is well-defined \emph{without the need of infinite counter terms.} It naturally leads to a covariant phase space in which the Hamiltonians generating asymptotic symmetries provide the total energy-momentum and angular momentum of the space-time. We address the subtle but important problems that arise because of logarithmic translations and super-translations both in the Langrangian and Hamiltonian frameworks. As a forthcoming paper will show, the treatment of higher dimensions is considerably simpler. Our first order framework also suggests a new direction for generalizing the spectral action of non-commutative geometry.

v1 (Mon, 18 Feb 2008 20:00:06 GMT), v2 (Wed, 19 Mar 2008 21:11:31 GMT)

Nitish Korula

Chandra Chekuri, Nitish Korula

Chekuri Chandra, Korula Nitish

Min-Cost 2-Connected Subgraphs With k Terminals

18 pages, 3 figures

cs.DS

In the k-2VC problem, we are given an undirected graph G with edge costs and an integer k; the goal is to find a minimum-cost 2-vertex-connected subgraph of G containing at least k vertices. A slightly more general version is obtained if the input also specifies a subset S \subseteq V of terminals and the goal is to find a subgraph containing at least k terminals. Closely related to the k-2VC problem, and in fact a special case of it, is the k-2EC problem, in which the goal is to find a minimum-cost 2-edge-connected subgraph containing k vertices. The k-2EC problem was introduced by Lau et al., who also gave a poly-logarithmic approximation for it. No previous approximation algorithm was known for the more general k-2VC problem. We describe an O(\log n \log k) approximation for the k-2VC problem.

v1 (Mon, 18 Feb 2008 18:34:28 GMT)

Juergen Horbach

Ali Kerrache (University of Mainz), Juergen Horbach (German Aerospace Center, Koeln), and Kurt Binder (University of Mainz)

Kerrache Ali, Horbach Juergen, Binder Kurt

Molecular Dynamics Computer Simulation of Crystal Growth and Melting in Al50Ni50

6 pages, 6 figures

Europhys. Lett. 81, 58001 (2008)

10.1209/0295-5075/81/58001

cond-mat.mtrl-sci cond-mat.stat-mech

The melting and crystallization of Al50Ni50} are studied by means of molecular dynamics computer simulations, using a potential of the embedded atom type to model the interactions between the particles. Systems in a slab geometry are simulated where the B2 phase of AlNi in the middle of an elongated simulation box is separated by two planar interfaces from the liquid phase, thereby considering the (100) crystal orientation. By determining the temperature dependence of the interface velocity, an accurate estimate of the melting temperature is provided. The value k=0.0025 m/s/K for the kinetic growth coefficient is found. This value is about two orders of magnitude smaller than that found in recent simulation studies of one-component metals. The classical Wilson-Frenkel model is not able to describe the crystal growth kinetics on a quantitative level. We argue that this is due to the neglect of diffusion processes in the liquid-crystal interface.

v1 (Mon, 18 Feb 2008 18:41:54 GMT)

Zhi-Hui Guo

Zhi-Hui Guo

Guo Zhi-Hui

Resonance sum rules from large $N_C$ and partial wave dispersive analysis

4 pages, contribution to the Workshop on "Scalar meson and Related topics" (Scadron 70), during Feb 11-16, 2008, at IST, Lisbon, Portugal

10.1063/1.2973540

hep-ph

Combining large $N_C$ techniques and partial wave dispersion theory to analyze the $\pi\pi$ scattering, without relying on any explicit resonance lagrangian, some interesting results are derived: (a) a general KSRF relation including the scalar meson contribution; (b) a new relation between resonance couplings, with which we have made an intensive analysis in several specific models; (c) low energy constants in chiral perturbation theory related with $\pi\pi$ scattering in terms of the mass and decay width of resonances.

v1 (Mon, 18 Feb 2008 18:45:51 GMT)

Iosif Galanakis

I. Galanakis, K. Ozdogan and E. Sasioglu

Galanakis I., Ozdogan K., Sasioglu E.

Ab-initio determined electronic and magnetic properties of half-metallic NiCrSi and NiMnSi Heusler alloys; the role of interfaces and defects

Journal of Applied Physics 104, 083916 (2008)

10.1063/1.3005882

cond-mat.mtrl-sci

Using state-of-the-art first-principles calculations we study the properties of the ferromagnetic Heusler compounds NiYSi where Y stands for V, Cr or Mn. NiCrSi and NiMnSi contrary to NiVSi are half-metallic at their equilibrium lattice constant exhibiting integer values of the total spin magnetic moment and thus we concentrate on these two alloys. The minority-spin gap has the same characteristics as for the well-known NiMnSb alloy being around $\sim$1 eV. Upon tetragonalization the gap is present in the density of states even for expansion or contraction of the out-of-plane lattice parameter by 5%. The Cr-Cr and Mn-Mn interactions make ferromagnetism extremely stable and the Curie temperature exceeds 1000 K for NiMnSi. Surface and interfaces with GaP, ZnS and Si semiconductors are not half-metallic but in the case of NiCrSi the Ni-based contacts present spin-polarization at the Fermi level over 90%. Finally, we show that there are two cases of defects and atomic-swaps. The first-ones which involve the Cr(Mn) and Si atoms induce states at the edges of the gap which persists for a moderate-concentration of defects. Defects involving Ni atoms induce states localized within the gap completely destroying the half-metallicity. Based on single-impurity calculations we associate these states to the symmetry of the crystal.

v1 (Mon, 18 Feb 2008 19:07:55 GMT)

Antonaldo Diaferio

A. Diaferio

Diaferio A.

The evidence for unusual gravity from the large-scale structure of the Universe

Invited review to appear in the Proceedings of the 1st AFI symposium "From the Vacuum to the Universe", Innsbruck, Austria, October 2007, to be published by the Innsbruck University Press, ed. by S.D. Bass, F. Schallhart and B. Tasser

astro-ph

Under the assumption that General Relativity (GR) correctly describes the phenomenology of our Universe, astronomical observations provide compelling evidence that (1) the dynamics of cosmic structure is dominated by dark matter (DM), an exotic matter mostly made of hypothetical elementary particles, and (2) the expansion of the Universe is currently accelerating because of the presence of a positive cosmological constant Lambda. The DM particles have not yet been detected and there is no theoretical justification for the tiny positive Lambda implied by observations. Therefore, over the last decade, the search for extended or alternative theories of gravity has flourished.

v1 (Mon, 18 Feb 2008 19:27:34 GMT)

Steve Fisk

Steve Fisk

Fisk Steve

Coloring the 600 Cell

4 pages

math.CO

The 600 cell S has exactly 10 5-colorings. From these colorings we can construct the space of colorings $B(S)$. This complex has 1344 colorings, and is isomorphic to the space of 5 by 5 Latin Squares. These simplices split into 4 copies of a quotient of S by an involution, and two copies of a space made up of even Latin Squares.

v1 (Mon, 18 Feb 2008 19:12:13 GMT)

Roya Mohayaee

Roya Mohayaee, Jacques Colin

Mohayaee Roya, Colin Jacques

Dark matter accretion wakes of high-redshift black holes

Talk presented at "Jean-Pierre Lasota, X-ray binaries, accretion disks and compact stars" (October 2007); Abramowicz, M. Ed., New Astronomy Review, in press

New Astron.Rev.51:898-905,2008

10.1016/j.newar.2008.03.022

astro-ph

Anisotropic emission of gravitational waves during the merger or formation of black holes can lead to the ejection of these black holes from their host galaxies. A recoiled black hole which moves on an almost radial bound orbit outside the virial radius of its central galaxy, in the cold dark matter background, reaches its apapsis in a finite time. The low value of dark matter velocity dispersion at high redshifts and also the black hole velocity near the apapsis passage yield a high-density wake around these black holes. Gamma-ray emission can result from the enhancement of dark matter annihilation in these wakes. The diffuse high-energy gamma-ray background from the ensemble of such black holes in the Hubble volume is also evaluated.

v1 (Mon, 18 Feb 2008 20:11:39 GMT)

Ryan Porter

G.J. Ferland, A.C. Fabian, N.A. Hatch, R.M. Johnstone, R.L. Porter, P.A.M. van Hoof, R.J.R. Williams

Ferland G. J., Fabian A. C., Hatch N. A., Johnstone R. M., Porter R. L., van Hoof P. A. M., Williams R. J. R.

The origin of molecular hydrogen emission in cooling-flow filaments

5 pages, 4 figures, accepted to MNRAS Letters

10.1111/j.1745-3933.2008.00463.x

astro-ph

The optical filaments found in many cooling flows in galaxy clusters consist of low density ($\sim 10^3 \pcc$) cool ($\sim 10^3$ K) gas surrounded by significant amounts of cosmic-ray and magnetic-field energy. Their spectra show anomalously strong low-ionization and molecular emission lines when compared with galactic molecular clouds exposed to ionizing radiation such as the Orion complex. Previous studies have shown that the spectra cannot be produced by O-star photoionization. Here we calculate the physical conditions in dusty gas that is well shielded from external sources of ionizing photons and is energized either by cosmic rays or dissipative MHD waves. Strong molecular hydrogen lines, with relative intensities similar to those observed, are produced. Selection effects introduced by the microphysics produce a correlation between the \htwo line upper level energy and the population temperature. These selection effects allow a purely collisional gas to produce \htwo emission that masquerades as starlight-pumped \htwo but with intensities that are far stronger. This physics may find application to any environment where a broad range of gas densities or heating rates occur.

v1 (Mon, 18 Feb 2008 20:41:01 GMT)

Luis Gonzalez-Mestres

Luis Gonzalez-Mestres

Gonzalez-Mestres Luis

Lorentz symmetry violation and the results of the AUGER experiment

Two sections added. 12 pages, LaTex

hep-ph

We briefly discuss the implications of recent AUGER results for patterns of Lorentz symmetry violation (LSV), assuming that the existence of the Greisen-Zatsepin-Kuzmin cutoff is definitely confirmed. The mass composition of the highest-energy cosmic-ray spectrum is a crucial issue. In any case, the new data allow in principle to exclude a significant range of LSV models but leave open several important possibilities : a weaker Lorentz breaking, a fundamental scale beyond the Planck scale, scenarios with threshold effects... It may even happen that spontaneous decays due to LSV fake the GZK cutoff. Space experiments appear to be needed to further test special relativity. We also comment on the consequences of AUGER data for superbradyons. If such particles are present in the Universe, they may provide new forms of dark matter and dark energy.

v1 (Mon, 18 Feb 2008 19:56:22 GMT), v2 (Mon, 25 Feb 2008 20:26:47 GMT), v3 (Mon, 16 Jun 2008 18:49:31 GMT)

Louis Marchildon

Louis Marchildon

Marchildon Louis

On relativistic elements of reality

Clarifications, reference added; published version

Foundations of Physics 38 (2008) 804-17

10.1007/s10701-008-9238-9

quant-ph

Several arguments have been proposed some years ago, attempting to prove the impossibility of defining Lorentz-invariant elements of reality. I find that a sufficient condition for the existence of elements of reality, introduced in these proofs, seems to be used also as a necessary condition. I argue that Lorentz-invariant elements of reality can be defined but, as Vaidman pointed out, they won't satisfy the so-called product rule. In so doing I obtain algebraic constraints on elements of reality associated with a maximal set of commuting Hermitian operators.

v1 (Mon, 18 Feb 2008 20:25:41 GMT), v2 (Fri, 24 Oct 2008 11:48:36 GMT)

Mladen Georgiev

Mladen Georgiev

Georgiev Mladen

Note on the oblate and prolate deformations in nuclear matter from the viewpoint of the quantum-mechanical off-center effect

7 pages including 1 figure, all pdf format

nucl-th

We consider the possibility that a quantum-mechanical off-center effect may be behind the deformed oblate and prolate shapes of nuclei in nuclear physics. In solid state physics, finite off-center displacements result from the mixing of electronic states through their coupling to vibrational (phonon) modes of appropriate symmetries. This is an example of fermion-boson interaction which may materialize in nuclear physics as well in the form of a coupling of nucleons to the pi-meson field. We carry out calculations to substantiate the proposal.

v1 (Mon, 18 Feb 2008 20:27:26 GMT)

Songxue Chi

Songxue Chi, Pengcheng Dai, T. Barnes, H. J. Kang, J. W. Lynn, R. Bewley, F. Ye, M. B. Maple, Z. Henkie, and A. Pietraszko

Chi Songxue, Dai Pengcheng, Barnes T., Kang H. J., Lynn J. W., Bewley R., Ye F., Maple M. B., Henkie Z., Pietraszko A.

Inelastic neutron scattering studies of Crystal Field Levels in PrOs$_4$As$_{12}$

7 pages, 7 figures

Phys. Rev. B 77, 094428 (2008)

10.1103/PhysRevB.77.094428

cond-mat.str-el

We use neutron scattering to study the Pr$^{3+}$ crystalline electric field (CEF) excitations in the filled skutterudite PrOs$_4$As$_{12}$. By comparing the observed levels and their strengths under neutron excitation with the theoretical spectrum and neutron excitation intensities, we identify the Pr$^{3+}$ CEF levels, and show that the ground state is a magnetic $\Gamma_4^{(2)}$ triplet, and the excited states $\Gamma_1$, $\Gamma_4^{(1)}$ and $\Gamma_{23}$ are at 0.4, 13 and 23 meV, respectively. A comparison of the observed CEF levels in PrOs$_4$As$_{12}$ with the heavy fermion superconductor PrOs$_4$Sb$_{12}$ reveals the microscopic origin of the differences in the ground states of these two filled skutterudites.

v1 (Tue, 19 Feb 2008 00:12:13 GMT)

Tilo Waldenmaier

Tilo Waldenmaier

Waldenmaier Tilo

IceTop - Cosmic Ray Physics with IceCube

4 pages, 6 figures. Talk at Roma International Conference on Astroparticle Physics, June 2007

Nucl.Instrum.Meth.A588:130-134,2008

10.1016/j.nima.2008.01.015

astro-ph

The IceCube experiment at South Pole consists of two detector components - the IceTop air shower array on the surface and the neutrino telescope at depths from 1450 m to 2450 m below. Currently, 26 IceTop stations and 22 InIce strings are deployed. With the present size of the IceTop array, it is possible to measure cosmic rays with energies ranging from 0.5 to 100 PeV. Coincident events between the IceTop and the InIce detector provide useful cross-checks of the detector performance and furthermore make it possible to study the cosmic-ray composition. This paper gives an overview on the current status of IceTop.

v1 (Tue, 19 Feb 2008 00:21:25 GMT)

Romain Tessera

Romain Tessera

Tessera Romain

Coarse embeddings into a Hilbert space, Haagerup Property and Poincare inequalities

14 pages

math.GT

We prove that a metric space does not coarsely embed into a Hilbert space if and only if it satisfies a sequence of Poincar\'e inequalities, which can be formulated in terms of (generalized) expanders. We also give quantitative statements, relative to the compression. In the equivariant context, our result says that a group does not have the Haagerup property if and only if it has relative property T with respect to a family of probabilities whose supports go to infinity. We give versions of this result both in terms of unitary representations, and in terms of affine isometric actions on Hilbert spaces.

v1 (Tue, 19 Feb 2008 00:27:14 GMT), v2 (Tue, 11 Mar 2008 20:56:44 GMT)

Kimball A. Milton

I. Brevik and K. A. Milton

Brevik I., Milton K. A.

Casimir Energies: Temperature Dependence, Dispersion, and Anomalies

15 pages, no figures; slight revision of discussion

Phys.Rev.E78:011124,2008

10.1103/PhysRevE.78.011124

quant-ph hep-th

Assuming the conventional Casimir setting with two thick parallel perfectly conducting plates of large extent with a homogeneous and isotropic medium between them, we discuss the physical meaning of the electromagnetic field energy $W_{\rm disp}$ when the intervening medium is weakly dispersive but nondissipative. The presence of dispersion means that the energy density contains terms of the form $d[\omega\epsilon(\omega)] /d\omega$ and $d[\omega\mu(\omega)] /d\omega$. We find that, as $W_{\rm disp}$ refers thermodynamically to a non-closed physical system, it is {\it not} to be identified with the internal thermodynamic energy $U$ following from the free energy $F$, or the electromagnetic energy $W$, when the last-mentioned quantities are calculated without such dispersive derivatives. To arrive at this conclusion, we adopt a model in which the system is a capacitor, linked to an external self-inductance $L$ such that stationary oscillations become possible. Therewith the model system becomes a non-closed one. As an introductory step, we review the meaning of the nondispersive energies, $F, U,$ and $W$. As a final topic, we consider an anomaly connected with local surface divergences encountered in Casimir energy calculations for higher spacetime dimensions, $D>4$, and discuss briefly its dispersive generalization. This kind of application is essentially a generalization of the treatment of Alnes {\it et al.} [J. Phys. A: Math. Theor. {\bf 40}, F315 (2007)] to the case of a medium-filled cavity between two hyperplanes.

v1 (Mon, 18 Feb 2008 21:49:28 GMT), v2 (Mon, 5 May 2008 22:45:53 GMT), v3 (Tue, 17 Jun 2008 18:01:04 GMT)

Novella Bartolini

Novella Bartolini, Giancarlo Bongiovanni, Simone Silvestri (Department of Computer Science University of Rome Sapienza, Italy)

Bartolini Novella, Bongiovanni Giancarlo, Silvestri Simone

Self-* overload control for distributed web systems

The full version of this paper, titled "Self-* through self-learning: overload control for distributed web systems", has been published on Computer Networks, Elsevier. The simulator used for the evaluation of the proposed algorithm is available for download at the address: http://www.dsi.uniroma1.it/~novella/qos_web/

cs.NI cs.PF

Unexpected increases in demand and most of all flash crowds are considered the bane of every web application as they may cause intolerable delays or even service unavailability. Proper quality of service policies must guarantee rapid reactivity and responsiveness even in such critical situations. Previous solutions fail to meet common performance requirements when the system has to face sudden and unpredictable surges of traffic. Indeed they often rely on a proper setting of key parameters which requires laborious manual tuning, preventing a fast adaptation of the control policies. We contribute an original Self-* Overload Control (SOC) policy. This allows the system to self-configure a dynamic constraint on the rate of admitted sessions in order to respect service level agreements and maximize the resource utilization at the same time. Our policy does not require any prior information on the incoming traffic or manual configuration of key parameters. We ran extensive simulations under a wide range of operating conditions, showing that SOC rapidly adapts to time varying traffic and self-optimizes the resource utilization. It admits as many new sessions as possible in observance of the agreements, even under intense workload variations. We compared our algorithm to previously proposed approaches highlighting a more stable behavior and a better performance.

v1 (Mon, 18 Feb 2008 21:18:17 GMT), v2 (Thu, 29 Jan 2009 15:14:20 GMT)

Cynthia Will

Cynthia E. Will

Will Cynthia E.

A curve of nilpotent Lie algebras which are not Einstein nilradicals

10 pages

math.DG math-ph math.MP math.RT

The only known examples of noncompact Einstein homogeneous spaces are standard solvmanifolds (special solvable Lie groups endowed with a left invariant metric), and according to a long standing conjecture, they might be all. The classification of Einstein solvmanifolds is equivalent to the one of Einstein nilradicals, i.e. nilpotent Lie algebras which are nilradicals of the Lie algebras of Einstein solvmanifolds. Up to now, there have been found very few examples of graded nilpotent Lie algebras that can not be Einstein nilradicals. In particular, in each dimension, there are only finitely many known. We exhibit in the present paper two curves of pairwise non-isomorphic 9-dimensional 2-step nilpotent Lie algebras which are not Einstein nilradicals.

v1 (Mon, 18 Feb 2008 21:00:11 GMT)

Isabelle Dicaire

I. Dicaire (1), C. Carignan (1), P. Amram (2), M. Marcelin (2), J. Hlavacek-Larrondo (1), M.-M. de Denus-Baillargeon (1), O. Daigle (1,2) and O. Hernandez (1) ((1) Universit\'e de Montr\'eal, (2) LAM-Marseille)

Dicaire I., Carignan C., Amram P., Marcelin M., Hlavacek-Larrondo J., de Denus-Baillargeon M. -M., Daigle O., Hernandez O.

Deep Fabry-Perot Halpha Observations of NGC 7793: a Very Extended Halpha Disk and a Truly Declining Rotation Curve

28 pages, 8 figures. Accepted for publication in AJ

10.1088/0004-6256/135/6/2038

astro-ph

Deep Halpha observations of the Sculptor Group galaxy NGC 7793 were obtained on the ESO 3.60m and the Marseille 36cm telescopes at La Silla, Chile. Halpha emission is detected all the way to the edge of the HI disk, making of the HII disk of NGC 7793 one of the largest ever observed in a quiet non-AGN late-type system. Even in the very outer parts, the HII ionizing sources are probably mainly internal (massive stars in the disk) with an unlikely contribution from the extragalactic ionizing background. The Halpha kinematics confirms what had already been seen with the HI observations: NGC 7793 has a truly declining rotation curve. However, the decline is not Keplerian and a dark halo is still needed to explain the rotation velocities in the outer parts.

v1 (Mon, 18 Feb 2008 21:00:31 GMT)

Igor Herbut

Igor F. Herbut and Bitan Roy

Herbut Igor F., Roy Bitan

Quantum critical scaling in magnetic field near the Dirac point in graphene

5 RevTex pages, 3 figures; added comments and references; cosmetic changes (this, published, version)

Phys. Rev. B vol. 77, 245438 (2008)

10.1103/PhysRevB.77.245438

cond-mat.mes-hall cond-mat.str-el

Motivated by the recent measurement of the activation energy at the quantum Hall state at the filling factor f=1 in graphene we discuss the scaling of the interaction-induced gaps in vicinity of the Dirac point with the magnetic field. The gap at f=1 is shown to be bounded from above by E(1)/C, where E(n) are the Landau level energies and C = 5.985 + O(1/N) is a universal number. The universal scaling functions are computed exactly for a large number of Dirac fermions N. We find a sublinear dependence of the gap at the laboratory magnetic fields for realistic values of short-range repulsion between electrons, and in quantitative agreement with observation.

v1 (Mon, 18 Feb 2008 21:00:37 GMT), v2 (Fri, 11 Apr 2008 21:51:09 GMT), v3 (Sun, 29 Jun 2008 09:41:16 GMT)

Rene Fassbender

R. Fassbender, H. Boehringer, G. Lamer, C.R. Mullis, P. Rosati, A. Schwope, J. Kohnert, J.S. Santos

Fassbender R., Boehringer H., Lamer G., Mullis C. R., Rosati P., Schwope A., Kohnert J., Santos J. S.

Indications for 3 Mpc-scale large-scale structure associated with an X-ray luminous cluster of galaxies at z=0.95

5 pages, 4 figures, accepted for publication in A&A

10.1051/0004-6361:20079001

astro-ph

X-ray luminous clusters of galaxies at z~1 are emerging as major cosmological probes and are fundamental tools to study the cosmic large-scale structure and environmental effects of galaxy evolution at large look-back times. We present details of the newly-discovered galaxy cluster XMMU J0104.4-0630 at z=0.947 and a probable associated system in the LSS environment. The clusters were found in a systematic study for high-redshift systems using deep archival XMM-Newton data for the serendipitous detection and the X-ray analysis, complemented by optical/NIR imaging observations and spectroscopy of the main cluster. We find a well-evolved, intermediate luminosity cluster with Lx=(6.4+-1.3)x10^43 erg/s (0.5-2.0 keV) and strong central 1.4 GHz radio emission. The cluster galaxy population exhibits a pronounced transition toward bluer colors at cluster-centric distances of 1-2 core radii, consistent with an age difference of 1-2 Gyr for a single burst solar metallicity model. The second, less evolved X-ray cluster at a projected distance of 6.4 arcmin (~3 Mpc) and a concordant red-sequence color likely forms a cluster-cluster bridge with the main target as part of its surrounding large-scale structure at z~0.95.

v1 (Tue, 19 Feb 2008 09:53:12 GMT)

Asle Sudbo

E. K. Dahl, E. Babaev, S. Kragset, and A. Sudbo

Dahl E. K., Babaev E., Kragset S., Sudbo A.

Preemptive vortex-loop proliferation in multicomponent interacting Bose--Einstein condensates

12 pages, 10 figures. Submitted to Physical Review B

Phys.Rev.B77:144519,2008

10.1103/PhysRevB.77.144519

cond-mat.stat-mech hep-th

We use analytical arguments and large-scale Monte Carlo calculations to investigate the nature of the phase transitions between distinct complex superfluid phases in a two-component Bose--Einstein condensate when a non-dissipative drag between the two components is being varied. We focus on understanding the role of topological defects in various phase transitions and develop vortex-matter arguments allowing an analytical description of the phase diagram. We find the behavior of fluctuation induced vortex matter to be much more complex and substantially different from that of single-component superfluids. We propose and investigate numerically a novel drag-induced ``preemptive vortex loop proliferation'' transition. Such a transition may be a quite generic feature in many multicomponent systems where symmetry is restored by a gas of several kinds of competing vortex loops.

v1 (Mon, 18 Feb 2008 21:01:50 GMT)

Sean McGee

D. J. Wilman (1), D. Pierini (1), K. Tyler (2), S. L. McGee (3), A. Oemler Jr (4), S. L. Morris (5), M. L. Balogh (3), R. G. Bower (5), J. S. Mulchaey (4) ((1) MPE, Garching, Germany, (2) Steward Observatory, Arizona, (3) University of Waterloo, Canada, (4) Carnegie Observatories, Pasadena, (5) University of Durham, U.K.)

Wilman D. J., Pierini D., Tyler K., McGee S. L., Oemler A., Morris S. L., Balogh M. L., Bower R. G., Mulchaey J. S.

Unveiling the Important Role of Groups in the Evolution of Massive Galaxies: Insights from an Infrared Passive Sequence at Intermediate Redshift

15 pages, 6 figures. Accepted for publication in ApJ

10.1086/587478

astro-ph

The most massive galaxies in the Universe are also the oldest. To overturn this apparent contradiction with hierarchical growth models, we focus on the group scale haloes which host most of these galaxies. A stellar mass selected M_* >~ 2x10^10M_sol sample at z~0.4 is constructed within the CNOC2 redshift survey. A sensitive Mid InfraRed (MIR) IRAC colour is used to isolate passive galaxies. It produces a bimodal distribution, in which passive galaxies (highlighted by morphological early-types) define a tight MIR colour sequence (Infrared Passive Sequence, IPS). This is due to stellar atmospheric emission from old stellar populations. Significantly offset from the IPS are galaxies where reemission by dust boosts emission at 8microns (InfraRed-Excess or IRE galaxies). They include all known morphological late-types. Comparison with EW[OII] shows that MIR colour is highly sensitive to low levels of activity, and allows us to separate dusty-active from passive galaxies. The fraction of IRE galaxies, f(IRE) drops with M_*, such that f(IRE)=0.5 at a ``crossover mass'' of ~1.3x10^11M_sol. Within our optically-defined group sample there is a strong and consistent deficit in f(IRE) at all masses, and most clearly at M_* >~10^11M_sol. Using a mock galaxy catalogue derived from the Millenium Simulation we show that the observed trend of f(IRE) with M_* can be explained if suppression of star formation occurs primarily in the group environment, and particularly for M_*>~10^11M_sol galaxies. In this way, downsizing can be driven solely by structure growth in the Universe.

v1 (Mon, 18 Feb 2008 21:03:22 GMT)

Bridget Tenner

Kari Ragnarsson and Bridget Eileen Tenner

Ragnarsson Kari, Tenner Bridget Eileen

Obtainable Sizes of Topologies on Finite Sets

Final version, to appear in Journal of Combinatorial Theory, Series A

math.CO math.GN

We study the smallest possible number of points in a topological space having k open sets. Equivalently, this is the smallest possible number of elements in a poset having k order ideals. Using efficient algorithms for constructing a topology with a prescribed size, we show that this number has a logarithmic upper bound. We deduce that there exists a topology on n points having k open sets, for all k in an interval which is exponentially large in n. The construction algorithms can be modified to produce topologies where the smallest neighborhood of each point has a minimal size, and we give a range of obtainable sizes for such topologies.

v1 (Mon, 18 Feb 2008 21:13:48 GMT), v2 (Mon, 3 Mar 2008 14:53:45 GMT), v3 (Mon, 6 Oct 2008 20:01:29 GMT), v4 (Wed, 20 May 2009 19:20:27 GMT)

Sebastian Commichau S.C.C.

S.C. Commichau, A. Biland, J. L. Contreras, R. de los Reyes, A. Moralejo, J. Sitarek and D. Sobczynska

Commichau S. C., Biland A., Contreras J. L., Reyes R. de los, Moralejo A., Sitarek J., Sobczynska D.

Monte Carlo Studies of Geomagnetic Field Effects on the Imaging Air Cherenkov Technique for the MAGIC Telescope Site

minor text changes

Nucl.Instrum.Meth.A595:572-586,2008

10.1016/j.nima.2008.07.144

astro-ph

Imaging air Cherenkov telescopes (IACTs) detect the Cherenkov light from extensive air showers (EAS) initiated by very high energy (VHE) gamma-rays impinging on the Earth's atmosphere. Due to the overwhelming background from hadron induced EAS, the discrimination of the rare gamma-like events is vital. The influence of the geomagnetic field (GF) on the development of EAS can further complicate the imaging air Cherenkov technique. The amount and the angular distribution of Cherenkov light from EAS can be obtained by means of Monte Carlo (MC) simulations. Here we present the results from dedicated MC studies of GF effects on images from gamma-ray initiated EAS for the MAGIC telescope site, where the GF strength is ~40 micro Tesla. The results from the MC studies suggest that GF effects degrade not only measurements of very low energy gamma-rays below ~100 GeV but also those at TeV-energies.

v1 (Mon, 18 Feb 2008 21:14:25 GMT), v2 (Mon, 19 May 2008 08:18:28 GMT), v3 (Tue, 20 May 2008 09:40:43 GMT), v4 (Fri, 25 Jul 2008 07:44:57 GMT)

John H. Debes

J. H. Debes, M. Lopez-Morales

Debes J. H., Lopez-Morales M.

A Second Look at the Metal Line Variability of G29-38

14 pages, 4 figures, Accepted to ApJL

10.1086/587550

astro-ph

The pulsating white dwarf G29-38 possesses a dust disk and metal lines attributed to the accretion of its disk material. \citet{vonhipg29} have reported variability in the equivalent width of G29-38's CaII K line on the timescale of days. We use high resolution optical spectroscopy of G29-38's CaII K line to test this observation. Over six days spanning in June 2007 and October 2007 we see no evidence for variability in the equivalent width of the Ca II K line. We also sample the variability of the Ca II K line over integrated timescales of $\sim$100-500 seconds, where errors from incomplete coverage of pulsation modes are predicted to be $\sim$8-15%. We find that the scatter of the equivalent widths over this time period is consistent with measurement errors at the 7% level, slightly weaker than predicted but within the uncertainties of predictions. Weaker Ca and Mg lines observed show no significant variability on yearly timescales over ten years based on our data and other high resolution spectra. We conclude that further study is warranted to verify if the accretion onto G29-38 is variable.

v1 (Mon, 18 Feb 2008 21:26:12 GMT)

Jose D'Incao

J. P. D'Incao, B. D. Esry, and Chris H. Greene

D'Incao J. P., Esry B. D., Greene Chris H.

Ultracold atom-molecule collisions with fermionic atoms

6 pages, 2 figures

Phys. Rev. A 77, 052709 (2008)

10.1103/PhysRevA.77.052709

physics.atom-ph

Elastic and inelastic properties of weakly bound s- and p-wave molecules of fermionic atoms that collide with a third atom are investigated. Analysis of calculated collisional properties of s-wave dimers of fermions in different spin states permit us to compare and highlight the physical mechanisms that determine the stability of s-wave and p-wave molecules. In contrast to s-wave molecules, the collisional properties of p-wave molecules are found to be largely insensitive to variations of the p-wave scattering length and that these collisions will usually result in short molecular lifetimes. We also discuss the importance of this result for both theories and experiments involving degenerate Fermi gases.

v1 (Mon, 18 Feb 2008 21:27:03 GMT), v2 (Wed, 20 Feb 2008 15:42:04 GMT)

Volodymyr Nekrashevych

Volodymyr Nekrashevych

Nekrashevych Volodymyr

Free subgroups in groups acting on rooted trees

math.GR

We show that if a group $G$ acting faithfully on a rooted tree $T$ has a free subgroup, then either there exists a point $w$ of the boundary $\partial T$ and a free subgroup of $G$ with trivial stabilizer of $w$, or there exists $w\in\partial T$ and a free subgroup of $G$ fixing $w$ and acting faithfully on arbitrarily small neighborhoods of $w$. This can be used to prove absence of free subgroups for different known classes of groups. For instance, we prove that iterated monodromy groups of expanding coverings have no free subgroups and give another proof of a theorem by S. Sidki.

v1 (Mon, 18 Feb 2008 21:42:00 GMT)

Sebastien Ragot

Ragot Sebastien

Sebastien Ragot

Comments on the Hartree-Fock description of the Hooke's atom and suggestion for an accurate closed-form orbital

10 pages, submitted to JCP

S. Ragot. J. Chem. Phys. 128, 164104 (2008)

physics.atom-ph physics.chem-ph

The ground-state Hartree-Fock (HF) wavefunction of the Hooke's atom is not known in closed form, contrary to the exact solution. The single HF orbital involved has thus far been studied using expansion techniques only, leading to slightly disparate energies. Therefore, the present letter aims at proposing alternative definitions of the HF wavefunction. First, the HF limit is ascertained using a simple expansion, which makes it possible to formulate explicit expressions of HF properties. The resulting energy, 2.038 438 871 8 Eh, is found stable at the tenth digit. Second and more instructive, an analysis of the Hartree equation makes it possible to infer a remarkably simple and accurate HF orbital, leading to an energy exceeding by 5.76 10-7 Eh only the above HF limit. This orbital makes it possible to obtain (near) Hartree-Fock properties in closed-form, which in turn enables handy comparisons with exact quantities.

v1 (Mon, 18 Feb 2008 21:50:34 GMT)

Gopal Narayanan

Gopal Narayanan, Mark H. Heyer, Christopher Brunt, Paul F. Goldsmith, Ronald Snell, and Di Li

Narayanan Gopal, Heyer Mark H., Brunt Christopher, Goldsmith Paul F., Snell Ronald, Li Di

The Five College Radio Astronomy Observatory CO Mapping Survey of the Taurus Molecular Cloud

35 pages, 22 figures, Accepted for publication in Astrophysical Journal Supplement Series; The figures have been compressed in this version. Full-resolution figures of paper available at http://www.astro.umass.edu/~gopal/taurus-datapaper/

10.1086/587786

astro-ph

The FCRAO Survey of the Taurus Molecular Cloud observed the 12CO and 13CO J=1-0 emission from 98 square degrees of this important, nearby star forming region. This set of data with 45" resolution comprises the highest spatial dynamic range image of an individual molecular cloud constructed to date, and provides valuable insights to the molecular gas distribution, kinematics, and the star formation process. In this contribution, we describe the observations, calibration, data processing, and characteristics of the noise and line emission of the survey. The angular distribution of 12CO and 13CO emission over 1 km/s velocity intervals and the full velocity extent of the cloud are presented. These reveal a complex, dynamic medium of cold, molecular gas.

v1 (Mon, 18 Feb 2008 21:56:13 GMT)

Guglielmo Fucci

Guglielmo Fucci and Ivan G. Avramidi

Fucci Guglielmo, Avramidi Ivan G.

Non-commutative Corrections in Spectral Matrix Gravity

32 Pages, LaTex. Some nonessential typos in intermediate calculations in sect. 3 and 4 are corrected. The final results are the same

Class.Quant.Grav.26:045019,2009

10.1088/0264-9381/26/4/045019

gr-qc

We study a non-commutative deformation of general relativity based on spectral invariants of a partial differential operator acting on sections of a vector bundle over a smooth manifold. We compute the first non-commutative corrections to Einstein equations in the weak deformation limit and analyze the spectrum of the theory. Related topics are discussed as well.

v1 (Mon, 18 Feb 2008 21:58:03 GMT), v2 (Fri, 22 Jan 2010 15:56:37 GMT)

Ken-Ichi Nishikawa

K.-I. Nishikawa (NSSTC/Uah) P. Hardee (UA) Y. Mizuno (NASA/MSFC/NSSTC) M. Medvedev (U. Kansas) B. Zhang (UNLV) D. H. Hartmann (Clemson U.) G. J. Fishman (NASA/MSFC)

Nishikawa K. -I., Hardee P., Mizuno Y., Medvedev M., Zhang B., Hartmann D. H., Fishman G. J.

Relativistic Particle-In-Cell Simulation Studies of Prompt and Early Afterglows from GRBs

19 pages,7 figures, contributed talk at Seventh European Workshop on Collisionless Shocks, Paris, 7- 9 November 2007. High resolution version can be obtained at http://gammaray.nsstc.nasa.gov/~nishikawa/shockws07.pdf

AIP Conf.Proc.1000:393-396,2008

10.1063/1.2943492

astro-ph

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks e.g. gamma-ray bursts (GRBs) active galactic nuclei (AGNs) and microquasars commonly exhibit power-law emission spectra. Recent PIC simulations of relativistic electron-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless relativistic shocks particle (electron, positron and ion) acceleration is due to plasma waves and their associated instabilities (e.g. the Weibel (filamentation) instability) created in the shock region. The simulations show that the Weibel instability is responsible for generating and amplifying highly non-uniform small-scale magnetic fields. These fields contribute to the electron's transverse deflection behind the jet head. The resulting ``jitter'' radiation from deflected electrons has different properties compared to synchrotron radiation which assumes a uniform magnetic field. Jitter radiation may be important for understanding the complex time evolution and/or spectra in gamma-ray bursts, relativistic jets in general and supernova remnants.

v1 (Mon, 18 Feb 2008 22:01:48 GMT)

Eugene Eliseev

Eugene A. Eliseev, Anna N. Morozovska, Sergei V. Kalinin, Yulan L. Li, Jie Shen, Maya D. Glinchuk, Long-Qing Chen, and Venkatraman Gopalan

Eliseev Eugene A., Morozovska Anna N., Kalinin Sergei V., Li Yulan L., Shen Jie, Glinchuk Maya D., Chen Long-Qing, Gopalan Venkatraman

Surface Effect on Domain Wall Width in Ferroelectrics

36 pages, 7 Figures, 1 Table, 3 Appendices, to be submitted to Phys. Rev. B

10.1063/1.3236644

cond-mat.mtrl-sci

We study the effect of depolarization field related with inhomogeneous polarization distribution, strain and surface energy parameters on a domain wall profile near the surface of a ferroelectric film within the framework of Landau-Ginzburg-Devonshire phenomenology. Both inhomogeneous elastic stress and positive surface energy lead to the wall broadening at electrically screened surface. For ferroelectrics with weak piezoelectric coupling, the extrapolation length that defines surface energy parameter, affects the wall broadening more strongly than inhomogeneous elastic stress. Unexpectedly, the domain wall profile follows a long-range power law when approaching the surface, while it saturates exponentially in the bulk. In materials with high piezoelectric coupling and negligibly small surface energy (i.e. high extrapolation length) inhomogeneous elastic stress effect dominates.

v1 (Mon, 18 Feb 2008 22:04:42 GMT), v2 (Sat, 3 May 2008 15:32:25 GMT)

Horacio E. Castillo

Azita Parsaeian and Horacio E. Castillo

Parsaeian Azita, Castillo Horacio E.

Equilibrium and non-equilibrium fluctuations in a glass-forming liquid

v1: 5 pages, 4 figures v2: 5 pages, 4 figures. Now includes results at three temperatures, two of them above T_{MCT} and one below T_{MCT}; and more extensive discussion of connections to experiments

Phys. Rev. Lett. 102, 055704 (2009)

10.1103/PhysRevLett.102.055704

cond-mat.dis-nn cond-mat.soft cond-mat.stat-mech

Glass-forming liquids display strong fluctuations -- dynamical heterogeneities -- near their glass transition. By numerically simulating a binary Weeks-Chandler-Andersen liquid and varying both temperature and timescale, we investigate the probability distributions of two kinds of local fluctuations in the non-equilibrium (aging) regime and in the equilibrium regime; and find them to be very similar in the two regimes and across temperatures. We also observe that, when appropriately rescaled, the integrated dynamic susceptibility is very weakly dependent on temperature and very similar in both regimes.

v1 (Mon, 18 Feb 2008 22:14:16 GMT), v2 (Mon, 17 Nov 2008 08:21:53 GMT)

Sebastien Ragot

Ragot Sebastien

Sebastien Ragot

Comments on the momentum density and the spatial form of the density-matrix of the Hooke's atom

7 pages. Submitted

Phys. Rev. A 78, 016502 (2008)

10.1103/PhysRevA.78.016502

physics.atom-ph physics.chem-ph

In a recent paper, A. Akbari, N. H. March and A. Rubio [Phys. Rev. A. 76, 032510 (2007)] have investigated the one-electron reduced density-matrix and the momentum density of several two-electron model atoms, including the Hooke's atom. The method used by the authors for deriving an integral form of the momentum density is well suited for deriving a closed-form expression of the exact reciprocal form factor, which function is of importance inasmuch as it reflects the off-diagonal side of the exact reduced density-matrix.

v1 (Mon, 18 Feb 2008 22:18:34 GMT)

Sinhue Amos Refugio Haro Corzo

Sinhue A.R. Haro-Corzo, Luc Binette, Yair Krongold

Haro-Corzo Sinhue A. R., Binette Luc, Krongold Yair

The big blue bump and soft X-ray excess of individual quasars

3 pages, 1 figure, conference

astro-ph

For 11 quasar, we find that the soft X-ray excess component is not prolongation of the Big Blue Bump. Furthermore, adopting a theoretical continuum that is absorbed by the appropriate amount of intrinsic dust, we are able to reconcile this universal theoretical continuum with the UV break and the softness problem. Para 11 quasares, encontramos que el exceso de rayos-X suaves no es una prolongacion de la Gran Joroba Azul. Aun mas, adoptando un continuo ionizante teorico absorbido por una cantidad diversa de polvo intrinseco para cada quasar, podemos reconciliar este continuo teorico con el quiebre UV con el problema de suavidad.

v1 (Mon, 18 Feb 2008 22:20:24 GMT)

Gerald A. Miller

Gerald A. Miller

Miller Gerald A.

Meson Clouds and Nucleon Electromagnetic Form Factors

8 pages 4 figures. This is a written version of a talk presented at the workshop "Exclusive Reactions at High Momentum Transfer" May 21-24, 2007 Jefferson Lab, Newport News, VA USA Replacement makes the abstract and text consistent with Fig.4

10.1142/9789812796950_0009

nucl-th hep-ph nucl-ex

In contrast with common non-relativistic lore, the usual Sachs form factors are not the Fourier transforms of charge or magnetization densities. Instead, the two-dimensional Fourier transform of the electromagnetic $F_1$ form factor is the charge charge density of partons in the transverse plane. An analysis of the available data for neutron form factors leads to the result that the neutron charge density is negative at the center, and that the square of the transverse charge radius is positive. This contrasts with many expectations. Additionally, the use of measured proton form factors leads to the result that the proton's central $u$ quark charge density is larger than that of the $d$ quark by about 80%. The proton (neutron) charge density has a long range positively (negatively) charged component indicative of a pion cloud.

v1 (Mon, 18 Feb 2008 22:24:38 GMT), v2 (Wed, 20 Feb 2008 22:16:05 GMT)

Jun Wu

Jun Wu, Yue-Jin Tan, Hong-Zhong Deng, Yong Li, Bin Liu, Xin Lv

Wu Jun, Tan Yue-Jin, Deng Hong-Zhong, Li Yong, Liu Bin, Lv Xin

Spectral Measure of Robustness in Complex Networks

4 pages, 2 figures

cond-mat.stat-mech cond-mat.dis-nn math.CO

We introduce the concept of natural connectivity as a robustness measure of complex networks. The natural connectivity has a clear physical meaning and a simple mathematical formulation. It characterizes the redundancy of alternative paths by quantifying the weighted number of closed walks of all lengths. We show that the natural connectivity can be derived mathematically from the graph spectrum as an average eigenvalue and that it increases strictly monotonically with the addition of edges. We test the natural connectivity and compare it with other robustness measures within a scenario of edge elimination. We demonstrate that the natural connectivity has an acute discrimination which agrees with our intuition.

v1 (Mon, 18 Feb 2008 22:58:08 GMT)

Gvozden Rukavina

Gvozden Rukavina

Rukavina Gvozden

Quadratic recurrence equations - exact explicit solution of period four fixed points functions in bifurcation diagram

20 pages, 6 figures

nlin.CD

This article presents the exact solution of fixed points functions for the cycle of period four of the quadratic recurrence equations. The solution is demonstrated for the quadratic map and the logistic map. These recurrence equations, presenting the real domain, as well as the Mandelbrot set, presenting the complex domain, are at the very heart of dynamical systems and chaos theory. Up to now, the closed explicit solutions of fixed points functions have only been known for three bifurcation ranges: for the cycles of period one, two and three. With the discovery of the solution for cycle four, disclosed in this paper, further step has been made in our comprehension of simultaneous complexity and simplicity which represents the beauty of nature.

v1 (Tue, 19 Feb 2008 19:12:31 GMT)

Peggy Li H.Y.

R.F. Bishop, P.H.Y. Li, R. Darradi, and J. Richter

Bishop R. F., Li P. H. Y., Darradi R., Richter J.

The quantum $J_{1}$--$J_{1}'$--$J_{2}$ spin-1 Heisenberg model: Influence of the interchain coupling on the ground-state magnetic ordering in 2D

6 pages. 3 figures. Minor changes in content

Europhys. Lett. 83 (2008) 47004

10.1088/0953-8984/20/25/255251

cond-mat.str-el

We study the phase diagram of the isotropic $J_{1}$--$J_{1}'$--$J_{2}$ Heisenberg model for spin-1 particles on an anisotropic square lattice, using the coupled cluster method. We find no evidence for an intermediate phase between the N\'{e}el and stripe states, as compared with all previous results for the corresponding spin-1/2 case. However, we find a quantum tricritical point at $J_{1}'/J_{1} \approx0.66 \pm 0.03$, $J_{2}/J_{1} \approx0.35\pm0.02$, where a line of second-order phase transitions between the quasi-classical N\'{e}el and stripe-ordered phases (for $J_{1}'/J_{1} \lesssim 0.66$) meets a line of first-order phase transitions between the same two states (for $J_{1}'/J_{1} \gtrsim 0.66$)

v1 (Mon, 18 Feb 2008 22:40:17 GMT), v2 (Mon, 21 Apr 2008 17:53:21 GMT), v3 (Sat, 14 Jun 2008 12:36:32 GMT)

Leandro Vendramin

S. Freyre, M. Gra\~na, L. Vendramin

Freyre S., Graña M., Vendramin L.

On Nichols algebras over PGL(2,q) and PSL(2,q)

Minor changes

J. Algebra Appl., Vol. 9, No. 2 (2010) 195-208

10.1142/S0219498810003823

math.QA

We compute necessary conditions on Yetter-Drinfeld modules over the groups $\mathbf{PGL}(2,q)=\mathbf{PGL}(2,\FF_q)$ and $\mathbf{PSL}(2,q)=\mathbf{PSL}(2,\FF_q)$ to generate finite dimensional Nichols algebras. This is a first step towards a classification of pointed Hopf algebras with group of group-likes isomorphic to one of these groups. As a by-product of the techniques developed in this work, we prove that there is no non-trivial finite-dimensional pointed Hopf algebra over the Mathieu groups $M_{20}$ and $M_{21}=\mathbf{PSL}(3,4)$.

v1 (Tue, 19 Feb 2008 11:04:20 GMT), v2 (Fri, 20 Mar 2009 19:18:42 GMT), v3 (Mon, 23 Mar 2009 22:07:07 GMT)

Can Kilic

Can Kilic, Takemichi Okui, Raman Sundrum

Kilic Can, Okui Takemichi, Sundrum Raman

Colored Resonances at the Tevatron: Phenomenology and Discovery Potential in Multijets

20 pages, 7 figures, pdflatex. Version to be published in JHEP, paragraphs added discussing the phenomenology beyond the benchmark model, one reference added

JHEP 0807:038,2008

10.1088/1126-6708/2008/07/038

hep-ph hep-ex

There exist several classes of theories beyond the Standard Model which contain massive spin-1 color octets, generically called "colorons". Indeed we argue that colorons inevitably appear in the spectrum whenever new colored particles feel an additional confining force. Colorons are distinctive at hadron colliders as this is the only environment in which they can be resonantly produced. In the simplest models we show that the coloron naturally decays to multijets via secondary resonances, which can be consistent with all existing bounds, even for colorons as light as a few hundred GeV. We perform representative case studies and show that a search in the four-jet channel at the Tevatron has strong signal significance, while the LHC faces formidable challenges for such a search.

v1 (Tue, 19 Feb 2008 20:07:45 GMT), v2 (Tue, 26 Feb 2008 17:58:40 GMT), v3 (Tue, 1 Jul 2008 19:22:09 GMT)

Kimball A. Milton

K. A. Milton

Milton K. A.

Coulomb Resummation and Monopole Masses

12 pages, 7 eps figures. Talk given in memory of I.L. Solovtsov at Seminar in Bogoliubov Laboratory of Theoretical Physics, JINR, Dubna, Russia in January 2008

hep-ph hep-ex

The relativistic Coulomb resummation factor suggested by I.L. Solovtsov is used to reanalyze the mass limits obtained for magnetic monopoles which might have been produced at the Fermilab Tevatron. The limits given by the Oklahoma experiment (Fermilab E882) are pushed close to the unitary bounds, so that the lower limits on monopole masses are increased from around 250 GeV to about 400 GeV.

v1 (Mon, 18 Feb 2008 23:45:44 GMT)

Jian Song

Jian Song, Gang Tian

Song Jian, Tian Gang

Canonical measures and Kahler-Ricci flow

56 pages

math.DG math.AG

We show that the Kahler-Ricci flow on an algebraic manifold of positive Kodaira dimension and semi-ample canonical line bundle converges to a unique canonical metric on its canonical model. It is also shown that there exists a canonical measure of analytic Zariski decomposition on an algebraic manifold of positive Kodaira dimension. Such a canonical measure is unique and invariant under birational transformations under the assumption of the finite generation of canonical rings.

v1 (Tue, 19 Feb 2008 04:13:45 GMT)

Christopher Thompson

Christopher Thompson

Thompson Christopher

Electrodynamics of Magnetars III: Pair Creation Processes in an Ultrastrong Magnetic Field and Particle Heating in a Dynamic Magnetosphere

25 pages, submitted to the Astrophysical Journal

10.1086/592263

astro-ph

We consider the details of the QED processes that create electron-positron pairs in magnetic fields approaching and exceeding 10^{14} G. The formation of free and bound pairs is addressed, and the importance of positronium dissociation by thermal X-rays is noted. We calculate the collision cross section between an X-ray and a gamma ray, and point out a resonance in the cross section when the gamma ray is close to the threshold for pair conversion. We also discuss how the pair creation rate in the open-field circuit and the outer magnetosphere can be strongly enhanced by instabilities near the light cylinder. When the current has a strong fluctuating component, a cascade develops. We examine the details of particle heating, and show that a high rate of pair creation can be sustained close to the star, but only if the spin period is shorter than several seconds. The dissipation rate in this turbulent state can easily accommodate the observed radio output of the transient radio-emitting magnetars, and even their infrared emission. Finally, we outline how a very high rate of pair creation on the open magnetic field lines can help to stabilize a static twist in the closed magnetosphere and to regulate the loss of magnetic helicity by reconnection at the light cylinder.

v1 (Tue, 19 Feb 2008 17:29:44 GMT)

Christopher Thompson

Christopher Thompson

Thompson Christopher

Electrodynamics of Magnetars IV: Self-Consistent Model of the Inner Accelerator, with Implications for Pulsed Radio Emission

32 pages, submitted to the Astrophysical Journal

10.1086/592061

astro-ph

We consider the voltage structure in the open-field circuit and outer magnetosphere of a magnetar. The standard polar-cap model for radio pulsars is modified significantly when the polar magnetic field exceeds 1.8x10^{14} G. Pairs are created by accelerated particles via resonant scattering of thermal X-rays, followed by the nearly instantaneous conversion of the scattered photon to a pair. A surface gap is then efficiently screened by e+- creation, which regulates the voltage in the inner part of the circuit to ~10^9 V. We also examine the electrostatic gap structure that can form when the magnetic field is somewhat weaker, and deduce a voltage 10-30 times larger over a range of surface temperatures. We examine carefully how the flow of charge back to the star above the gap depends on the magnitude of the current that is extracted from the surface of the star, on the curvature of the magnetic field lines, and on resonant drag. The rates of different channels of pair creation are determined self-consistently, including the non-resonant scattering of X-rays, and collisions between gamma rays and X-rays. We find that the electrostatic gap solution has too small a voltage to sustain the observed pulsed radio output of magnetars unless i) the magnetic axis is nearly aligned with the rotation axis and the light of sight; or ii) the gap is present on the closed as well as the open magnetic field lines. Several properties of the radio magnetars -- their rapid variability, broad pulses, and unusually hard radio spectra -- are consistent with a third possibility, that the current in the outer magnetosphere is strongly variable, and a very high rate of pair creation is sustained by a turbulent cascade.

v1 (Tue, 19 Feb 2008 16:10:04 GMT)

Jiangming Zhang

J. M. Zhang, W. M. Liu, and D. L. Zhou

Zhang J. M., Liu W. M., Zhou D. L.

Mean-field dynamics of a Bose Josephson junction in an optical cavity

revised according to the comments of the referee

Phys.Rev.A, 78, 043618 (2008)

10.1103/PhysRevA.78.043618

quant-ph cond-mat.stat-mech

We study the mean-field dynamics of a Bose Josephson junction which is dispersively coupled to a single mode of a high-finesse optical cavity. An effective classical Hamiltonian for the Bose Josephson junction is derived and its dynamics is studied in the perspective of phase portrait. It is shown that the strong condensate-field coupling does alter the dynamics of the Bose Josephson junction drastically. The possibility of coherent manipulating and \textsl{in situ} observation of the dynamics of the Bose Josephson junction is discussed.

v1 (Tue, 19 Feb 2008 01:40:00 GMT), v2 (Thu, 21 Feb 2008 16:03:39 GMT), v3 (Tue, 22 Apr 2008 12:35:20 GMT)

Terence H. Chan

Laurent Guille, Terence Chan and Alex Grant

Guille Laurent, Chan Terence, Grant Alex

The minimal set of Ingleton inequalities

cs.IT math.IT

The Ingleton-LP bound is an outer bound for the multicast capacity region, assuming the use of linear network codes. Computation of the bound is performed on a polyhedral cone obtained by taking the intersection of half-spaces induced by the basic (Shannon-type) inequalities and Ingleton inequalities. This paper simplifies the characterization of this cone, by obtaining the unique minimal set of Ingleton inequalities. As a result, the effort required for computation of the Ingleton-LP bound can be greatly reduced.

v1 (Tue, 19 Feb 2008 01:55:23 GMT)

Ian Agol

Ian Agol

Agol Ian

Pants immersed in hyperbolic 3-manifolds

12 pages, 4 figures

math.GT

We show that an immersed thrice-punctured sphere in a cusped orientable hyperbolic 3-manifold is either embedded or has a single clasp in a manifold obtained by hyperbolic Dehn filling on a cusp of the Whitehead link complement.

v1 (Tue, 19 Feb 2008 14:47:05 GMT)

Jeremy L. Martin

Art M. Duval, Caroline J. Klivans, Jeremy L. Martin

Duval Art M., Klivans Caroline J., Martin Jeremy L.

Simplicial matrix-tree theorems

36 pages, 2 figures. Final version, to appear in Trans. Amer. Math. Soc

Trans. Amer. Math. Soc. 361 (2009), no. 11, 6073-6114

math.CO

We generalize the definition and enumeration of spanning trees from the setting of graphs to that of arbitrary-dimensional simplicial complexes $\Delta$, extending an idea due to G. Kalai. We prove a simplicial version of the Matrix-Tree Theorem that counts simplicial spanning trees, weighted by the squares of the orders of their top-dimensional integral homology groups, in terms of the Laplacian matrix of $\Delta$. As in the graphic case, one can obtain a more finely weighted generating function for simplicial spanning trees by assigning an indeterminate to each vertex of $\Delta$ and replacing the entries of the Laplacian with Laurent monomials. When $\Delta$ is a shifted complex, we give a combinatorial interpretation of the eigenvalues of its weighted Laplacian and prove that they determine its set of faces uniquely, generalizing known results about threshold graphs and unweighted Laplacian eigenvalues of shifted complexes.

v1 (Tue, 19 Feb 2008 02:04:49 GMT), v2 (Thu, 21 Aug 2008 11:54:37 GMT)

Tao Zhou

Wei Hong, Xiaopu Han, Tao Zhou, and Binghong Wang

Hong Wei, Han Xiaopu, Zhou Tao, Wang Binghong

Heavy-tailed statistics in short-message communication

4 pages, 4 figures and 1 table

Chinese Physics Letters 26 (2009) 028902

10.1088/0256-307X/26/2/028902

physics.soc-ph physics.data-an

Short-message (SM) is one of the most frequently used communication channels in the modern society. In this Brief Report, based on the SM communication records provided by some volunteers, we investigate the statistics of SM communication pattern, including the interevent time distributions between two consecutive short messages and two conversations, and the distribution of message number contained by a complete conversation. In the individual level, the current empirical data raises a strong evidence that the human activity pattern, exhibiting a heavy-tailed interevent time distribution, is driven by a non-Poisson nature.

v1 (Tue, 19 Feb 2008 02:16:11 GMT)

Vladimir Avila-Reese

V. Avila-Reese (1), C. Firmani (1,2), G. Ghisellini (2), J. I. Cabrera (1) ((1)IA-UNAM, Mexico; (2) INAF-OAB, Italy)

Avila-Reese V., Firmani C., Ghisellini G., Cabrera J. I.

Gamma-Ray Bursts, new cosmological beacons

7 pages, 3 figures. Invited talk, to appear in RevMexAA Conf. Series (XII IAU Regional Latinamerican Meeting, Isla de Margarita, October 22-26). Corrected typos, added references

Rev.Mex.Astron.Astrof.Ser.Conf.35:188,2009

astro-ph

Long Gamma-Ray Bursts (GRBs) are the brightest electromagnetic explosions in the Universe, associated to the death of massive stars. As such, GRBs are potential tracers of the evolution of the cosmic massive star formation, metallicity, and Initial Mass Function. GRBs also proved to be appealing cosmological distance indicators. This opens a unique opportunity to constrain the cosmic expansion history up to redshifts 5-6. A brief review on both subjects is presented here.

v1 (Tue, 19 Feb 2008 02:18:28 GMT), v2 (Fri, 22 Feb 2008 19:13:05 GMT)

FengLan Shao

Yun-fei Wang, Feng-lan Shao, Jun Song, De-ming Wei, Qu-bing Xie

Wang Yun-fei, Shao Feng-lan, Song Jun, Wei De-ming, Xie Qu-bing

Centrality dependence of $p_{T}$ spectra for identified hadrons in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}= 200$ GeV

7 pages, 6 figures

Chinese Physics C32, 976 (2008)

10.1088/1674-1137/32/12/007

hep-ph

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at $\sqrt{s_{NN}}= 200$ GeV is systematically studied in a quark combination model. The $\mathrm{{p}_{T}}$ spectra of $\pi^{\pm}$, $K^{\pm}$, $p(\bar{p})$ and $\Lambda(\bar{\Lambda})$ in different centrality bins and the nuclear modification factors ($R_{CP}$) for these hadrons are calculated. The centrality dependence of the average collective transverse velocity $<\beta (r)>$ for the hot and dense quark matter is obtained in Au+Au collisions, and it is applied to a relative smaller Cu+Cu collision system. The centrality dependence of $\mathrm{{p}_{T}}$ spectra and the $R_{CP}$ for $\pi^{0}$, $K_{s}^{0}$ and $\Lambda$ in Cu+Cu collisions at $\sqrt{s_{NN}}= 200$ GeV are well described. The results show that $<\beta (r)>$ is only a function of the number of participants $N_{part}$ and it is independent of the collision system.

v1 (Tue, 19 Feb 2008 02:36:33 GMT), v2 (Thu, 5 Mar 2009 07:22:53 GMT)

Luo

Feng Luo

Luo Feng

3-Dimensional Schlaefli Formula and Its Generalization

2 figure, 8 pages

math.GT math.MG

Several identities similar to the Schlaefli formula are established for tetrahedra in a space of constant curvature.

v1 (Tue, 19 Feb 2008 03:05:56 GMT)

Hisayuki Hara

Hisayuki Hara and Akimichi Takemura

Hara Hisayuki, Takemura Akimichi

A Localization Approach to Improve Iterative Proportional Scaling in Gaussian Graphical Models

12 pages

Communications in Statistics Theory and Methods, 39, No.8, 1643-1654, 2010

10.1080/03610920802238662

stat.CO stat.ME

We discuss an efficient implementation of the iterative proportional scaling procedure in the multivariate Gaussian graphical models. We show that the computational cost can be reduced by localization of the update procedure in each iterative step by using the structure of a decomposable model obtained by triangulation of the graph associated with the model. Some numerical experiments demonstrate the competitive performance of the proposed algorithm.

v1 (Tue, 19 Feb 2008 03:00:55 GMT), v2 (Wed, 28 May 2008 01:07:24 GMT)

Daniel Stolarski

Yasunori Nomura, Michele Papucci, Daniel Stolarski

Nomura Yasunori, Papucci Michele, Stolarski Daniel

Flavorful Supersymmetry from Higher Dimensions

31 pages, 2 figures; references and comments added

JHEP 0807:055,2008

10.1088/1126-6708/2008/07/055

hep-ph

We present models of flavorful supersymmetry in higher dimensions. The Higgs fields and the supersymmetry breaking field are localized in the same place in the extra dimension(s). The Yukawa couplings and operators generating the supersymmetry breaking parameters then receive the same suppression factors from the wavefunction profiles of the matter fields, leading to a specific correlation between these two classes of interactions. The resulting phenomenology is very rich, while stringent experimental constraints from the low-energy flavor and CP violating processes can all be satisfied. We construct both unified and non-unified models in this framework, which can be either strongly or weakly coupled at the cutoff scale. We analyze one version in detail, a strongly coupled unified model, which addresses various issues of supersymmetric grand unification. The models presented here provide an explicit example in which the supersymmetry breaking spectrum can be a direct window into the physics of flavor at a very high energy scale.

v1 (Tue, 19 Feb 2008 03:35:46 GMT), v2 (Thu, 15 May 2008 18:58:11 GMT)

Katie Freese

Katherine Freese, Matthew G. Brown, and William H. Kinney

Freese Katherine, Brown Matthew G., Kinney William H.

The Phantom Bounce: A New Proposal for an Oscillating Cosmology

New York Academy of Sciences Proceedings, Origins of Time's Arrow Conference, October 2007

astro-ph gr-qc hep-th

An oscillating universe cycles through a series of expansions and contractions. We propose a model in which ``phantom'' energy with a supernegative pressure ($p < - \rho$) grows rapidly and dominates the late-time expanding phase. The universe's energy density is then so large that the effects of quantum gravity are important at both the beginning and the end of each expansion (or contraction). The bounce can be caused by high energy modifications to the Friedmann equation governing the expansion of the universe, which make the cosmology nonsingular. The classic black hole overproduction of oscillating universes is resolved due to their destruction by the phantom energy.

v1 (Tue, 19 Feb 2008 03:57:20 GMT), v2 (Wed, 27 Feb 2008 22:16:59 GMT)

Taizan Watari

Minoru Kuriyama, Hiroto Nakajima and Taizan Watari

Kuriyama Minoru, Nakajima Hiroto, Watari Taizan

A Theoretical Framework for R-parity Violation

10.1103/PhysRevD.79.075002

hep-ph

We propose a theoretical framework for R-parity violation. It is realized by a class of Calabi--Yau compactification of Heterotic string theory. Trilinear R-parity violation in superpotential is either absent or negligibly small without an unbroken symmetry, due to a selection rule based on charge counting of a spontaneously broken U(1) symmetry. Although such a selection rule cannot be applied in general to non-renormalizable operators in the low-energy effective superpotential, it is valid for terms trilinear in low-energy degrees of freedom, and hence can be used as a solution to the dimension-4 proton decay problem in the minimal supersymmetric standard model. Bilinear R-parity violation is generated, but there are good reasons why they are small enough to satisfy its upper bounds from neutrino mass and washout of baryon/lepton asymmetry. All R-parity violating dimension-5 operators can be generated. In this theoretical framework, nucleons can decay through squark-exchange diagrams combining dimension-5 and bilinear R-parity violating operators. B-L breaking neutron decay is predicted.

v1 (Tue, 19 Feb 2008 20:52:48 GMT)

Keiko Kawamuro

Keiko Kawamuro

Kawamuro Keiko

Connect sum and transversely non simple knots

Following the referee, exposition is changed and misprints are corrected

10.1017/S0305004108002028

math.GT

We prove that transversal non-simplicity is preserved under taking connect sum, generalizing Vertesi's result.

v1 (Tue, 19 Feb 2008 20:49:23 GMT), v2 (Mon, 19 May 2008 21:53:54 GMT)

Jiaolin Xu

Jiao-Lin Xu

Xu Jiao-Lin

The New Symmetries Beyond the Standard Model (The Body-centred Cubic Periodic Symmetries in Particle Physics)

69 Pages, 8 Figures

physics.gen-ph hep-ph

This paper proposes new symmetries (the body-centred cubic periodic symmetries) beyond the standard model. Using a free particle expanded Schrodinger equation with the body-centred cubic periodic symmetry condition, the paper deduces a full baryon spectrum (including mass M, I, S, C, B, Q, J and P) of all 116 observed baryons. All quantum numbers of all deduced baryons are completely consistent with the corresponding experimental results. The deduced masses of all 116 baryons agree with (more than average 98 percent) the experimental baryon masses using only four constant parameters. The body-centred cubic periodic symmetries with a periodic constant ``a'' about $10^{-23}$m play a crucial rule. The results strongly suggest that the new symmetries really exist. This paper predicts some kind of ``Zeeman effect'' of baryons, for example: one experimental baryon N(1720)${3/2}^{+}$ with $ \Gamma$ = 200 Mev is composed of two N baryons [(N(1659)${3/2}^{+}$ + N(1839)${3/2}^{+}$] = $\bar{N(1749)}$${3/2}^{+}$ with $\Gamma$ = 1839-1659 = 180 Mev.

v1 (Tue, 19 Feb 2008 04:34:34 GMT), v2 (Tue, 19 Feb 2008 22:45:14 GMT)

Alexandros Dimakis

F. Benezit, A.G. Dimakis, P. Thiran, M. Vetterli

Benezit F., Dimakis A. G., Thiran P., Vetterli M.

Order-Optimal Consensus through Randomized Path Averaging

26 pages

cs.IT cs.NI math.IT math.PR

Gossip algorithms have recently received significant attention, mainly because they constitute simple and robust message-passing schemes for distributed information processing over networks. However for many topologies that are realistic for wireless ad-hoc and sensor networks (like grids and random geometric graphs), the standard nearest-neighbor gossip converges as slowly as flooding ($O(n^2)$ messages). A recently proposed algorithm called geographic gossip improves gossip efficiency by a $\sqrt{n}$ factor, by exploiting geographic information to enable multi-hop long distance communications. In this paper we prove that a variation of geographic gossip that averages along routed paths, improves efficiency by an additional $\sqrt{n}$ factor and is order optimal ($O(n)$ messages) for grids and random geometric graphs. We develop a general technique (travel agency method) based on Markov chain mixing time inequalities, which can give bounds on the performance of randomized message-passing algorithms operating over various graph topologies.

v1 (Tue, 19 Feb 2008 04:37:51 GMT)

Koji Maruyama

Koji Maruyama, Franco Nori

Maruyama Koji, Nori Franco

Entanglement purification without controlled-NOT gates by using the natural dynamics of spin chains

4 figures

Phys. Rev. A 78, 022312 (2008)

10.1103/PhysRevA.78.022312

quant-ph cond-mat.mes-hall

We present a simple protocol to purify bipartite entanglement in spin-1/2 particles by utilizing only natural spin-spin interactions, i.e. those that can commonly be realized in realistic physical systems, and S_z-measurements on single spins. Even the standard isotropic Heisenberg interaction is shown to be sufficient to purify mixed state entanglement if there are at least three pairs of spins. This approach could be useful for quantum information processing in solid-state-based systems.

v1 (Tue, 19 Feb 2008 04:43:44 GMT), v2 (Wed, 13 Aug 2008 03:40:20 GMT)

Daqing Wan

Chunlei Liu and Daqing Wan

Liu Chunlei, Wan Daqing

T-adic exponential sums over finite fields

new version, 21 pages, title is changed too

math.NT math.AG

$T$-adic exponential sums associated to a Laurent polynomial $f$ are introduced. They interpolate all classical $p^m$-power order exponential sums associated to $f$. The Hodge bound for the Newton polygon of $L$-functions of $T$-adic exponential sums is established. This bound enables us to determine, for all $m$, the Newton polygons of $L$-functions of $p^m$-power order exponential sums associated to an $f$ which is ordinary for $m=1$. Deeper properties of $L$-functions of $T$-adic exponential sums are also studied. Along the way, new open problems about the $T$-adic exponential sum itself are discussed.

v1 (Tue, 19 Feb 2008 04:49:15 GMT), v2 (Sun, 24 Feb 2008 00:40:48 GMT), v3 (Sun, 2 Mar 2008 03:55:28 GMT), v4 (Wed, 7 Jan 2009 06:01:49 GMT)

Bunei Sato

Bun'ei Sato, Hideyuki Izumiura, Eri Toyota, Eiji Kambe, Masahiro Ikoma, Masashi Omiya, Seiji Masuda, Yoichi Takeda, Daisuke Murata, Yoichi Itoh, Hiroyasu Ando, Michitoshi Yoshida, Eiichiro Kokubo, Shigeru Ida

Sato Bun'ei, Izumiura Hideyuki, Toyota Eri, Kambe Eiji, Ikoma Masahiro, Omiya Masashi, Masuda Seiji, Takeda Yoichi, Murata Daisuke, Itoh Yoichi, Ando Hiroyasu, Yoshida Michitoshi, Kokubo Eiichiro, Ida Shigeru

Planetary Companions around Three Intermediate-Mass G and K Giants: 18 Del, xi Aql, and HD 81688

28 pages, 9 figures, accepted for publication in PASJ

10.1093/pasj/60.3.539

astro-ph

We report the detection of 3 new extrasolar planets from the precise Doppler survey of G and K giants at Okayama Astrophysical Observatory. The host stars, namely, 18 Del (G6 III), xi Aql (K0 III) and HD 81688 (K0 III-IV), are located at the clump region on the HR diagram with estimated masses of 2.1-2.3 M_solar. 18 Del b has a minimum mass of 10.3 M_Jup and resides in a nearly circular orbit with period of 993 days, which is the longest one ever discovered around evolved stars. xi Aql b and HD 81688 b have minimum masses of 2.8 and 2.7 M_Jup, and reside in nearly circular orbits with periods of 137 and 184 days, respectively, which are the shortest ones among planets around evolved stars. All of the substellar companions ever discovered around possible intermediate-mass (1.7-3.9 M_solar) clump giants have semimajor axes larger than 0.68 AU, suggesting the lack of short-period planets. Our numerical calculations suggest that Jupiter-mass planets within about 0.5 AU (even up to 1 AU depending on the metallicity and adopted models) around 2-3 M_solar stars could be engulfed by the central stars at the tip of RGB due to tidal torque from the central stars. Assuming that most of the clump giants are post-RGB stars, we can not distinguish whether the lack of short-period planets is primordial or due to engulfment by central stars. Deriving reliable mass and evolutionary status for evolved stars is highly required for further investigation of formation and evolution of planetary systems around intermediate-mass stars.

v1 (Tue, 19 Feb 2008 05:19:59 GMT)

Scott Papp

S. B. Papp, J. M. Pino, and C. E. Wieman

Papp S. B., Pino J. M., Wieman C. E.

Studying a dual-species BEC with tunable interactions

cond-mat.other

We report on the observation of controllable spatial separation in a dual-species Bose-Einstein condensate (BEC) with $^{85}$Rb and $^{87}$Rb. Interparticle interactions between the different components can change the miscibility of the two quantum fluids. In our experiments, we clearly observe the immiscible nature of the two simultaneously Bose-condensed species via their spatial separation. Furthermore the $^{85}$Rb Feshbach resonance near 155 G is used to change them between miscible and immiscible by tuning the $^{85}$Rb scattering length. Our apparatus is also able to create $^{85}$Rb condensates with up to $8\times10^4$ atoms which represents a significant improvement over previous work.

v1 (Tue, 19 Feb 2008 07:38:49 GMT)

Eric Nordenstam

Eric Nordenstam

Nordenstam Eric

On the Shuffling Algorithm for Domino Tilings

17 pages, 2 figures

math.PR

We study the dynamics of a certain discrete model of interacting particles that comes from the so called shuffling algorithm for sampling a random tiling of an Aztec diamond. It turns out that the transition probabilities have a particularly convenient determinantal form. An analogous formula in a continuous setting has recently been obtained by Jon Warren studying certain model of interlacing Brownian motions which can be used to construct Dyson's non-intersecting Brownian motion. We conjecture that Warren's model can be recovered as a scaling limit of our discrete model and prove some partial results in this direction. As an application to one of these results we use it to rederive the known result that random tilings of an Aztec diamond, suitably rescaled near a turning point, converge to the GUE minor process.

v1 (Tue, 19 Feb 2008 05:58:09 GMT)

Masanori Hirai

M. Hirai, S. Kumano, M. Oka, and K. Sudoh

Hirai M., Kumano S., Oka M., Sudoh K.

Determination of f_0(980) Structure by Fragmentation Functions

4page, 2eps figures, To appear in the proceedings of Chiral Symmetry in Hadron and Nuclear Physics (Chiral 07), Osaka, Japan, 13-16 Nov. 2007

Mod.Phys.Lett.A23:2226-2229,2008

10.1142/S0217732308029071

hep-ph

We discuss internal structure of an exotic hadron by using fragmentation functions. The fragmentation functions for the f_0(980) meson are obtained by a global analysis of e^++e^- \to f_0+X data. Quark configuration of the f_0(980) could be determined by peak positions and second moments of the obtained fragmentation functions.

v1 (Tue, 19 Feb 2008 06:09:16 GMT)

Menelaos Karavelas

Menelaos I. Karavelas and Elias P. Tsigaridas

Karavelas Menelaos I., Tsigaridas Elias P.

Guarding curvilinear art galleries with vertex or point guards

35 pages, 24 figures

Comput. Geom. Theory Appl. 42(6-7):522-535, 2009

10.1016/j.comgeo.2008.11.002

cs.CG

One of the earliest and most well known problems in computational geometry is the so-called art gallery problem. The goal is to compute the minimum possible number guards placed on the vertices of a simple polygon in such a way that they cover the interior of the polygon. In this paper we consider the problem of guarding an art gallery which is modeled as a polygon with curvilinear walls. Our main focus is on polygons the edges of which are convex arcs pointing towards the exterior or interior of the polygon (but not both), named piecewise-convex and piecewise-concave polygons. We prove that, in the case of piecewise-convex polygons, if we only allow vertex guards, $\lfloor\frac{4n}{7}\rfloor-1$ guards are sometimes necessary, and $\lfloor\frac{2n}{3}\rfloor$ guards are always sufficient. Moreover, an $O(n\log{}n)$ time and O(n) space algorithm is described that produces a vertex guarding set of size at most $\lfloor\frac{2n}{3}\rfloor$. When we allow point guards the afore-mentioned lower bound drops down to $\lfloor\frac{n}{2}\rfloor$. In the special case of monotone piecewise-convex polygons we can show that $\lfloor\frac{n}{2}\rfloor$ vertex guards are always sufficient and sometimes necessary; these bounds remain valid even if we allow point guards. In the case of piecewise-concave polygons, we show that $2n-4$ point guards are always sufficient and sometimes necessary, whereas it might not be possible to guard such polygons by vertex guards. We conclude with bounds for other types of curvilinear polygons and future work.

v1 (Tue, 19 Feb 2008 06:10:17 GMT)

Mohammad Reza Setare

M. R. Setare and E. N. Saridakis

Setare M. R., Saridakis E. N.

Coupled oscillators as models of quintom dark energy

11 pages, no figures

Phys.Lett.B668:177-181,2008

10.1016/j.physletb.2008.08.033

hep-th

We investigate quintom cosmology in FRW universes using isomorphic models consisting of three coupled oscillators, one of which carries negative kinetic energy. In particular, we examine the cosmological paradigms of minimally-coupled massless quintom, of two conformally-coupled massive scalars and of conformally-coupled massive quintom, and we obtain their qualitative characteristics as well as their quantitative asymptotic behavior. For open or flat geometries, we find that, independently of the specific initial conditions, the universe is always led to an eternal expansion.

v1 (Tue, 19 Feb 2008 06:12:45 GMT), v2 (Wed, 24 Sep 2008 13:15:00 GMT)

Irine Peng

Irine Peng

Peng Irine

Coarse differentiation and quasi-isometries of a class of solvable Lie groups I

48 pages (10pt, wide textwidth), 8 figures

math.MG

This is the first of two papers which aim to understand quasi-isometries of a subclass of unimodular split solvable Lie groups. In the present paper, we show that locally (in a coarse sense), a quasi-isometry between two groups in this subclass is close to a map that respects their group structures.

v1 (Tue, 19 Feb 2008 06:17:39 GMT)

Chris Judge

Luc Hillairet and Chris Judge

Hillairet Luc, Judge Chris

The eigenvalues of the Laplacian on domains with small slits

29 pages, 3 figures

math.SP math.AP

We introduce a small slit into a planar domain and study the resulting effect upon the eigenvalues of the Laplacian. In particular, we show that as the length of the slit tends to zero, each real-analytic eigenvalue branch tends to an eigenvalue of the original domain. By combining this with our earlier work (arXiv:math/0703616), we obtain the following application: The generic multiply connected polygon has simple spectrum.

v1 (Tue, 19 Feb 2008 18:34:41 GMT)

FengLan Shao

De-ming Wei, Feng-lan Shao, Jun Song, Yun-fei Wang

Wei De-ming, Shao Feng-lan, Song Jun, Wang Yun-fei

Centrality, system size and energy dependences of charged-particle pseudo-rapidity distribution

12 pages, 8 figures

Int.J.Mod.Phys.A23:5217-5227,2008

10.1142/S0217751X08042560

hep-ph

Utilizing the three-fireball picture within the quark combination model, we study systematically the charged particle pseudorapidity distributions in both Au+Au and Cu+Cu collision systems as a function of collision centrality and energy, $\sqrt{s_{NN}}=$ 19.6, 62.4, 130 and 200 GeV, in full pseudorapidity range. We find that: (i)the contribution from leading particles to $dN_{ch}/d\eta$ distributions increases with the decrease of the collision centrality and energy respectively; (ii)the number of the leading particles is almost independent of the collision energy, but it does depend on the nucleon participants $N_{part}$; (iii)if Cu+Cu and Au+Au collisions at the same collision energy are selected to have the same $N_{part}$, the resulting of charged particle $dN/d\eta$ distributions are nearly identical, both in the mid-rapidity particle density and the width of the distribution. This is true for both 62.4 GeV and 200 GeV data. (iv)the limiting fragmentation phenomenon is reproduced. (iiv) we predict the total multiplicity and pseudorapidity distribution for the charged particles in Pb+Pb collisions at $\sqrt{s_{NN}}= 5.5$ TeV. Finally, we give a qualitative analysis of the $N_{ch}/<N_{part}/2>$ and $dN_{ch}/d\eta/<N_{part}/2>|_{\eta\approx0}$ as function of $\sqrt{s_{NN}}$ and $N_{part}$ from RHIC to LHC.

v1 (Tue, 19 Feb 2008 06:38:26 GMT), v2 (Thu, 5 Mar 2009 12:40:10 GMT)

Jonah Gollub

Jonah N. Gollub, Bijoy Kuanr, Zibigniew Celinski, Robert Camley, and David R. Smith

Gollub Jonah N., Kuanr Bijoy, Celinski Zibigniew, Camley Robert, Smith David R.

Small dimensional microstrips embedded with ferromagnetic layers: Numerical simulations and experimental results

6 pages, 5 figures

cond-mat.mtrl-sci

We use a numerical electromagnetic simulation software to investigate a filtering device consisting of a small dimensional microstrips embedded with a thin layer of ferromagnetic material and we compare our results to experimental results. We are able to show good correlation of simulation versus experiment for the magnitude of insertion loss and phase shift. The microstrips considered have dimensions on the order of the skin depth of the conductor and hence the field distribution is not easily calculated by analytic methods. We show that numerical simulation methods provide an accurate means of characterizing these structures.

v1 (Tue, 19 Feb 2008 06:40:20 GMT)

Biao Wu

Biao Wu, Qi Zhang and Jie Liu

Wu Biao, Zhang Qi, Liu Jie

Anomalous Monopole In an Interacting Boson System

4 pages, 3 figures

Phys. Lett. A375:545, 2011

10.1016/j.physleta.2010.12.030

cond-mat.other

Anomalous monopole of disk shape is found to exist in the semiclassical theory of a two-mode interacting boson system. The quantum origin of this anomaly is the collapsing or bundling of field lines of Berry curvature caused by the interaction between bosons in the semiclassical limit. The significance of this anomalous monopole is twofold: (1) it signals the failure of the von Neumann-Wigner theorem in the semiclassical limit; (2) it indicates a breakdown of the correspondence principle between quantum and classical dynamics.

v1 (Tue, 19 Feb 2008 07:20:05 GMT)

David Guery-Odelin

A. Couvert (LKB - Lhomond), M. Jeppesen (LKB - Lhomond), T. Kawalec (LKB - Lhomond), G. Reinaudi (LKB - Lhomond), R. Mathevet (LCAR), David Guery-Odelin (LKB - Lhomond, LCAR)

Couvert A., Jeppesen M., Kawalec T., Reinaudi G., Mathevet R., Guery-Odelin David

A quasi-monomode guided atom-laser from an all-optical Bose-Einstein condensate

Europhys. Lett. 83 (2008) 50001

10.1209/0295-5075/83/50001

cond-mat.other

We report the achievement of an optically guided and quasi-monomode atom laser, in all spin projection states ($m_F =$ -1, 0 and $+1$) of F=1 in Rubidium 87. The atom laser source is a Bose-Einstein condensate (BEC) in a crossed dipole trap, purified to any one spin projection state by a spin-distillation process applied during the evaporation to BEC. The atom laser is outcoupled by an inhomogenous magnetic field, applied along the waveguide axis. The mean excitation number in the transverse modes is $<n > = 0.65 \pm 0.05$ for $m_F = 0 $ and $<n > = 0.8 \pm 0.3$ for the low field seeker $m_F = -1$.

v1 (Tue, 19 Feb 2008 07:31:16 GMT), v2 (Mon, 15 Sep 2008 10:19:30 GMT)

Romain Bachelard

Romain Bachelard (CPT), Cristel Chandre (CPT), Michel Vittot (CPT)

Bachelard Romain, Chandre Cristel, Vittot Michel

Hamiltonian description of a self-consistent interaction between charged particles and electromagnetic waves

10.1103/PhysRevE.78.036407

physics.plasm-ph physics.optics

The Hamiltonian description of the self-consistent interaction between an electromagnetic plane-wave and a co-propagating beam of charged particles is considered. We show how the motion can be reduced to a one-dimensional Hamiltonian model (in a canonical setting) from the Vlasov-Maxwell Poisson brackets. The reduction to this paradigmatic Hamiltonian model is performed using a Lie algebraic formalism which allows us to remain Hamiltonian at each step of the derivation.

v1 (Tue, 19 Feb 2008 07:31:54 GMT)