Preferred frame parameters in the tensor-vector-scalar theory of gravity and its generalization

Abstract: The Tensor-Vector-Scalar theory of gravity, which was designed as a relativistic implementation to the modified dynamics paradigm, has fared quite well as an alternative to dark matter, on both galactic and cosmological scales. However, its performance in the solar system, as embodied in the post-Newtonian formalism, has not yet been fully investigated. Tamaki has recently attempted to calculate the preferred frame parameters for TeVeS, but ignored the cosmological value of the scalar field, thus concluding that the Newtonian potential must be static in order to be consistent with the vector equation. We show that when the cosmological value of the scalar field is taken into account, there is no constraint on the Newtonian potential; however, the cosmological value of the scalar field is tightly linked to the vector field coupling constant K, preventing the former from evolving as predicted by its equation of motion. We then proceed to investigate the post-Newtonian limit of a generalized version of TeVeS, with Æther type vector action, and show that its β,γand ξparameters are as in GR, while solar system constraints on the preferred frame parameters α_1 and α_2 can be satisfied within a modest range of small values of the scalar and vector fields coupling parameters, and for values of the cosmological scalar field consistent with evolution within the framework of existing models.

tensor-vector-scalar theory
gravity
preferred frame parameter


Violation of non-Gaussianity consistency relation in a single field inflationary model

Abstract: In this paper we present a simple, toy model of single field inflation in which the standard non-Gaussianity consistency condition is violated. In this model the curvature perturbations on super-horizon scales are not conserved and the decaying modes of perturbations are not negligible in the non-atractor phase. As a result a large local non-Gaussianity can be obtained in the squeezed limit which violates the standard non-Gaussianity consistency condition for the single field models.

non-gaussianity consistency relation
inflationary model
single field inflation


Axion Cosmology Revisited

Abstract: The misalignment mechanism for axion production depends on the temperature-dependent axion mass. The latter has recently been determined within the interacting instanton liquid model (IILM), and provides for the first time a well-motivated axion mass for all temperatures. We reexamine the constraints placed on the axion parameter space in the light of this new mass function. We find an accurate and updated constraint f_a ≤ 2.8(±2)× 10^11GeV or m_a ≥ 21(±2) μ eV from the misalignment mechanism in the classic axion window (thermal scenario). However, this is superseded by axion string radiation which leads to f_a ≲ 3.2^+4_-2× 10^10GeV or m_a ≳ 0.20 ^+0.2_-0.1meV. In this analysis, we take care to precisely compute the effective degrees of freedom and, to fill a gap in the literature, we present accurate fitting formulas. We solve the evolution equations exactly, and find that analytic results used to date generally underestimate the full numerical solution by a factor 2-3. In the inflationary scenario, axions induce isocurvature fluctuations and constrain the allowed inflationary scale H_I. Taking anharmonic effects into account, we show that these bounds are actually weaker than previously computed. Considering the fine-tuning issue of the misalignment angle in the whole of the anthropic window, we derive new bounds which open up the inflationary window near θ_a →π. In particular, we find that inflationary dark matter axions can have masses as high as 0.01–1meV, covering the whole thermal axion range, with values of H_I up to 10^9GeV. Quantum fluctuations during inflation exclude dominant dark matter axions with masses above m_a≲ 1meV.


Deriving an Accurate Formula of Scale-dependent Bias with Primordial Non-Gaussianity: An Application of the Integrated Perturbation Theory

Abstract: We apply the integrated perturbation theory (Matsubara 2011, PRD 83, 083518) to evaluate the scale-dependent bias in the presence of primordial non-Gaussianity. The integrated perturbation theory is a general framework of nonlinear perturbation theory, in which a broad class of bias models can be incorporated into perturbative evaluations of biased power spectrum and higher-order polyspectra. Approximations such as the high-peak limit or the peak-background split are not necessary to derive the scale-dependent bias in this framework. Applying the halo approach, previously known formulas are re-derived as limiting cases of a general formula in this work, and it is implied that modifications should be made in general situations. Effects of redshift-space distortions are straightforwardly incorporated. It is found that the slope of the scale-dependent bias on large scales is determined only by the behavior of primordial bispectrum in the squeezed limit, and is not sensitive to bias models in general. It is the amplitude of scale-dependent bias that is sensitive to the bias models. The effects of redshift-space distortions turn out to be quite small for the monopole component of the power spectrum, while the quadrupole component is proportional to the monopole component on large scales, and thus also sensitive to the primordial non-Gaussianity.

scale-dependent bias
non-gaussianity
integrated perturbation theory


Dependence of outer boundary condition on protoneutron star asteroseismology with gravitational-wave signatures

Abstract: To obtain the eigenfrequencies of a protoneutron star (PNS) in the postbounce phase of core-collapse supernovae (CCSNe), we perform a linear perturbation analysis of the angle-averaged PNS profiles using results from a general relativistic CCSN simulation of a 15 M_⊙ star. In this work, we investigate how the choice of the outer boundary condition could affect the PNS oscillation modes in the linear analysis. By changing the density at the outer boundary of the PNS surface in a parametric manner, we show that the eigenfrequencies strongly depend on the surface density. By comparing with the gravitational wave (GW) signatures obtained in the hydrodynamics simulation, the so-called surface g-mode of the PNS can be well ascribed to the fundamental oscillations of the PNS. The frequency of the fundamental oscillations can be fitted by a function of the mass and radius of the PNS similar to the case of cold neutron stars. In the case that the position of the outer boundary is chosen to cover not only the PNS but also the surrounding postshock region, we obtain the eigenfrequencies close to the modulation frequencies of the standing accretion-shock instability (SASI). However, we point out that these oscillation modes are unlikely to have the same physical origin of the SASI modes seen in the hydrodynamics simulation. We discuss possible limitations of applying the angle-averaged, linear perturbation analysis to extract the full ingredients of the CCSN GW signatures.

asteroseismology
core-collapse supernovae
neutron star


Fine-structure constant constraints on dark energy

Abstract: We use astrophysical and atomic clock tests of the stability of the fine-structure constant α, together with Type Ia supernova and Hubble parameter data, to constrain the simplest class of dynamical dark energy models where the same degree of freedom is assumed to provide both the dark energy and (through a dimensionless coupling, ζ, to the electromagnetic sector) the α variation. We show how current data tightly constrains a combination of ζ and the dark energy equation of state w_0. At the 95% confidence level and marginalizing over w_0 we find |ζ|<5×10^-6, with the atomic clock tests dominating the constraints. The forthcoming generation of high-resolution ultra-stable spectrographs will enable significantly tighter constraints.

dark energy
dimensionless coupling
electromagnetic sector
confidence level


Electron Injection by Whistler Waves in Non-relativistic Shocks

Abstract: Electron acceleration to non-thermal, ultra-relativistic energies ( 10-100 TeV) is revealed by radio and X-ray observations of shocks in young supernova remnants (SNRs). The diffusive shock acceleration (DSA) mechanism is usually invoked to explain this acceleration, but the way in which electrons are initially energized or 'injected' into this acceleration process starting from thermal energies is an unresolved problem. In this paper we study the initial acceleration of electrons in non-relativistic shocks from first principles, using two- and three-dimensional particle-in-cell (PIC) plasma simulations. We systematically explore the space of shock parameters (the Alfvénic Mach number, M_A, the shock velocity, v_sh, the angle between the upstream magnetic field and the shock normal, theta_Bn, and the ion to electron mass ratio, m_i/m_e). We find that significant non-thermal acceleration occurs due to the growth of oblique whistler waves in the foot of quasi-perpendicular shocks. The obtained electron energy distributions show power law tails with spectral indices up to alpha 3-4. The maximum energies of the accelerated particles are consistent with the electron Larmor radii being comparable to that of the ions, indicating potential injection into the subsequent DSA process. This injection mechanism, however, requires the shock waves to have fairly low Alfénic Mach numbers, M_A < 20, which is consistent with the theoretical conditions for the growth of whistler waves in the shock foot (M_A < (m_i/m_e)^1/2). Thus, if the whistler mechanism is the only robust electron injection process at work in SNR shocks, then SNRs that display non-thermal emission must have significantly amplified upstream magnetic fields. Such field amplification is likely achieved by the escaping cosmic rays, so electron and proton acceleration in SNR shocks must be interconnected.

whistler wave
non-relativistic shock
plasma simulation
electron injection process


Nonlinear reconstruction

Abstract: We present a direct approach to nonparametrically reconstruct the linear density field from an observed nonlinear map. We solve for the unique displacement potential consistent with the nonlinear density and positive definite coordinate transformation using a multigrid algorithm. We show that we recover the linear initial conditions up to the nonlinear scale (r_δ_rδ_L>0.5 for k≲1 h/Mpc) with minimal computational cost. This reconstruction approach generalizes the linear displacement theory to fully nonlinear fields, potentially substantially expanding the baryon acoustic oscillations and redshift space distortions information content of dense large scale structure surveys, including for example SDSS main sample and 21cm intensity mapping initiatives.

reconstruction
density field
displacement potential
definite coordinate transformation
initial condition


MOND as the weak field limit of an extended metric theory of gravity with a matter-curvature coupling

Abstract: In this article we construct an extended relativistic f(R) theory of gravity with matter-curvature couplings F(R,L_matt) for which its weak field limit of approximation recovers the simplest version of MOND. We do this by (a) performing an order of magnitude approach and (b) by perturbing the resulting field equations of the theory to the weakest field limit of approximation. We also compute the geodesic equation of the resulting theory and show that it has an extra force, a fact that commonly appears in general matter-curvature couplings. This arxiv version includes a section at the end with an Erratum.

field limit
gravity
matter-curvature coupling


Constraint on the early Universe by relic gravitational waves: From pulsar timing observations

Abstract: Recent pulsar timing observations by the Parkers Pulsar Timing Array and European Pulsar Timing Array teams obtained the constraint on the relic gravitational waves at the frequency f_*=1/ yr, which provides the opportunity to constrain H_*, the Hubble parameter when these waves crossed the horizon during inflation. In this paper, we investigate this constraint by considering the general scenario for the early Universe: we assume that the effective (average) equation-of-state w before the big bang nucleosynthesis stage is a free parameter. In the standard hot big-bang scenario with w=1/3, we find that the current PPTA result follows a bound H_*≤ 1.15×10^-1, and the EPTA result follows H_*≤ 6.92×10^-2. We also find that these bounds become much tighter in the nonstandard scenarios with w>1/3. When w=1, the bounds become H_*≤5.89×10^-3 for the current PPTA and H_*≤3.39×10^-3 for the current EPTA. In contrast, in the nonstandard scenario with w=0, the bound becomes H_*≤7.76 for the current PPTA.

early universe
relic gravitational wave
pulsar timing observation


CosmoBit: A GAMBIT module for computing cosmological observables and likelihoods

Abstract: We introduce CosmoBit, a module within the open-source GAMBIT software framework for exploring connections between cosmology and particle physics with joint global fits. CosmoBit provides a flexible framework for studying various scenarios beyond ΛCDM, such as models of inflation, modifications of the effective number of relativistic degrees of freedom, exotic energy injection from annihilating or decaying dark matter, and variations of the properties of elementary particles such as neutrino masses and the lifetime of the neutron. Many observables and likelihoods in CosmoBit are computed via interfaces to AlterBBN, CLASS, DarkAges, MontePython, MultiModeCode, and plc. This makes it possible to apply a wide range of constraints from large-scale structure, Type Ia supernovae, Big Bang Nucleosynthesis and the cosmic microwave background. Parameter scans can be performed using the many different statistical sampling algorithms available within the GAMBIT framework, and results can be combined with calculations from other GAMBIT modules focused on particle physics and dark matter. We include extensive validation plots and a first application to scenarios with non-standard relativistic degrees of freedom and neutrino temperature, showing that the corresponding constraint on the sum of neutrino masses is much weaker than in the standard scenario.

gambit module
likelihood
relativistic degree
big bang nucleosynthesis
cosmobit


Bose-Einstein condensate strings

Abstract: We consider the possible existence of gravitationally bound general relativistic strings consisting of Bose-Einstein condensate (BEC) matter which is described, in the Newtonian limit, by the zero temperature time-dependent nonlinear Schrödinger equation (the Gross-Pitaevskii equation), with repulsive interparticle interactions. In the Madelung representation of the wave function, the quantum dynamics of the condensate can be formulated in terms of the classical continuity equation and the hydrodynamic Euler equations. In the case of a condensate with quartic nonlinearity, the condensates can be described as a gas with two pressure terms, the interaction pressure, which is proportional to the square of the matter density, and the quantum pressure, which is without any classical analogue though, when the number of particles in the system is high enough, the latter may be neglected. Assuming cylindrical symmetry, we analyze the physical properties of the BEC strings in both the interaction pressure and quantum pressure dominated limits, by numerically integrating the gravitational field equations. In this way we obtain a large class of stable stringlike astrophysical objects, whose basic parameters (mass density and radius) depend sensitively on the mass and scattering length of the condensate particle, as well as on the quantum pressure of the Bose-Einstein gas.

relativistic string
einstein condensate
bose
dark matter


Mainly axion cold dark matter from natural supersymmetry

Abstract: By eschewing finetuning from the electroweak and QCD sectors of supersymmetry (natural supersymmetry or SUSY), and by invoking the Kim-Nilles solution to the SUSY mu problem, one is lead to models wherein the dark matter is comprised of a mixture of axions and higgsino-like WIMPs. Over a large range of Peccei-Quinn breaking scale f_a 10^9-10^12 GeV, one then expects about 90-95 matter. In such a scenario, both axion and WIMP direct detection may be expected.


Bipolar Harmonic encoding of CMB correlation patterns

Abstract: Deviations from statistical isotropy can be modeled in various ways, for instance, anisotropic cosmological models (Bianchi models), compact topologies and presence of primordial magnetic field. Signature of anisotropy manifests itself in CMB correlation patterns. Here we explore the symmetries of the correlation function and its implications on the observable measures constructed within the Bipolar harmonic formalism for these variety of models. Different quantifiers within the Bipolar harmonic representation are used to distinguish between plausible models of breakdown of statistical isotropy and as a spectroscopic tool for discriminating between distinct cosmic topology.

cmb correlation pattern
bipolar spherical harmonic
biposhs


Shark: introducing an open source, free and flexible semi-analytic model of galaxy formation

Abstract: We present a new, open source, free semi-analytic model (SAM) of galaxy formation, Shark, designed to be highly flexible and modular, allowing easy exploration of different physical processes and ways of modelling them. We introduce the philosophy behind Shark and provide an overview of the physical processes included in the model. Shark is written in C++11 and has been parallelized with OpenMP. In the released version (v1.1), we implement several different models for gas cooling, active galactic nuclei, stellar and photo-ionisation feedback, and star formation (SF). We demonstrate the basic performance of Shark using the Planck15 cosmology SURFS simulations, by comparing against a large set of observations, including: the stellar mass function (SMF) and stellar-halo mass relation at z=0-4; the cosmic evolution of the star formation rate density (SFRD), stellar mass, atomic and molecular hydrogen; local gas scaling relations; and structural galaxy properties, finding excellent agreement. Significant improvements over previous SAMs are seen in the mass-size relation for disks/bulges, the gas-stellar mass and stellar mass-metallicity relations. To illustrate the power of Shark in exploring the systematic effects of the galaxy formation modelling, we quantify how the scatter of the SF main sequence and the gas scaling relations changes with the adopted SF law, and the effect of the starbursts H_2 depletion timescale on the SFRD and Ω_ H_2. We compare Shark with other SAMs and the hydrodynamical simulation EAGLE, and find that SAMs have a much higher halo baryon fractions due to large amounts of intra-halo gas, which in the case of EAGLE is in the intergalactic medium.

open source
semi-analytic model
galaxy formation


Formation of the First Stars

Abstract: Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signaled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionizing photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Lambda Cold Dark Matter (LCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of 10^6 M_sun and collapsing at redshifts z 20-30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models.

star
primordial star formation
molecular hydrogen


High-Redshift Cosmography

Abstract: We constrain the parameters describing the kinematical state of the universe using a cosmographic approach, which is fundamental in that it requires a very minimal set of assumptions (namely to specify a metric) and does not rely on the dynamical equations for gravity. On the data side, we consider the most recent compilations of Supernovae and Gamma Ray Bursts catalogues. This allows to further extend the cosmographic fit up to z = 6.6, i.e. up to redshift for which one could start to resolve the low z degeneracy among competing cosmological models. In order to reliably control the cosmographic approach at high redshifts, we adopt the expansion in the improved parameter y = z/(1+z). This series has the great advantage to hold also for z > 1 and hence it is the appropriate tool for handling data including non-nearby distance indicators. We find that Gamma Ray Bursts, probing higher redshifts than Supernovae, have constraining power and do require (and statistically allow) a cosmographic expansion at higher order than Supernovae alone. Exploiting the set of data from Union and GRBs catalogues, we show (for the first time in a purely cosmographic approach parametrized by deceleration q_0, jerk j_0, snap s_0) a definitively negative deceleration parameter q_0 up to the 3σ confidence level. We present also forecasts for realistic data sets that are likely to be obtained in the next few years.

cosmography
redshift
powerful model-independent approach


Prospects of antideuteron detection from dark matter annihilations or decays at AMS-02 and GAPS

Abstract: The search for cosmic antideuterons has been proposed as a promising method to indirectly detect dark matter, due to the very small background flux from spallations expected at the energies relevant to experiments. The antideuteron flux from dark matter annihilations or decays is, however, severely constrained by the non-observation of an excess in the antiproton-to-proton fraction measured by PAMELA. In this paper we calculate, for representative dark matter annihilation and decay channels, upper limits on the number of antideuteron events at AMS-02 and GAPS from requiring that the associated antiproton flux is in agreement with the PAMELA data. To this end, we first analyze in detail the formation of antideuterons in the coalescence model using an event-by-event Monte Carlo simulation and using data from various high energy experiments. We find that the resulting coalescence momentum shows a dependence on the underlying process and on the center of mass energy involved. Then, we calculate, using a diffusion model, the flux of antideuterons at the Earth from dark matter annihilations or decays. Our results indicate that, despite the various sources of uncertainty, the observation of an antideuteron flux at AMS-02 or GAPS from dark matter annihilations or decays will be challenging.

dark matter annihilation
antideuteron flux
astrophysical background


Lorentz symmetry violation, dark matter and dark energy

Abstract: Taking into account the experimental results of the HiRes and AUGER collaborations, the present status of bounds on Lorentz symmetry violation (LSV) patterns is discussed. Although significant constraints will emerge, a wide range of models and values of parameters will still be left open. Cosmological implications of allowed LSV patterns are discussed focusing on the origin of our Universe, the cosmological constant, dark matter and dark energy. Superbradyons (superluminal preons) may be the actual constituents of vacuum and of standard particles, and form equally a cosmological sea leading to new forms of dark matter and dark energy.

dark matter
dark energy
lorentz symmetry violation


Exoplanet Detection Methods

Abstract: This chapter reviews various methods of detecting planetary companions to stars from an observational perspective, focusing on radial velocities, astrometry, direct imaging, transits, and gravitational microlensing. For each method, this chapter first derives or summarizes the basic observable phenomena that are used to infer the ex- istence of planetary companions, as well as the physical properties of the planets and host stars that can be derived from the measurement of these signals. This chapter then outlines the general experimental requirements to robustly detect the signals us- ing each method, by comparing their magnitude to the typical sources of measurement uncertainty. This chapter goes on to compare the various methods to each other by outlining the regions of planet and host star parameter space where each method is most sensitive, stressing the complementarity of the ensemble of the methods at our disposal. Finally, there is a brief review of the history of the young exoplanet field, from the first detections to current state-of-the-art surveys for rocky worlds.

radial velocity
planet
exoplanet
one-parameter degeneracy


New decay modes of gravitino dark matter

Abstract: We consider the three-body decays of gravitino dark matter in supersymmetric scenarios with bilinear R-parity violation. In particular, gravitino decays into lepton+W^* (lepton ff̅') and ν+Z^* (νff̅) are examined for gravitino masses below Mw. After computing the gravitino decay rates into these three-body final states and studying their dependence on supersymmetric parameters, we find that these new decay modes are often more important than the two-body decay, into a photon and a neutrino, considered in previous works. Consequently, the gravitino lifetime and its branching ratios are substantially modified, with important implications for the indirect detection of gravitino dark matter.


Coupling matter in modified Q-gravity

Abstract: We present a novel theory of gravity by considering an extension of symmetric teleparallel gravity. This is done by introducing, in the framework of the metric-affine formalism, a new class of theories where the nonmetricity Q is nonminimally coupled to the matter Lagrangian. More specifically, we consider a Lagrangian of the form L ∼ f_1(Q) + f_2(Q) L_M, where f_1 and f_2 are generic functions of Q, and L_M is the matter Lagrangian. This nonminimal coupling entails the nonconservation of the energy-momentum tensor, and consequently the appearance of an extra force. The motivation is to verify whether the subtle improvement of the geometrical formulation, when implemented in the matter sector, would allow more universally consistent and viable realisations of the nonminimal curvature-matter coupling theories. Furthermore, we consider several cosmological applications by presenting the evolution equations and imposing specific functional forms of the functions f_1(Q) and f_2(Q), such as power-law and exponential dependencies of the nonminimal couplings. Cosmological solutions are considered in two general classes of models, and found to feature accelerating expansion at late times.

symmetric teleparallel gravity
metric-affine formalism
matter lagrangian


Distinguishing cosmologies using the turn-around radius near galaxy clusters

Abstract: Outside galaxy clusters the competition between the inwards gravitational attraction and the outwards expansion of the Universe leads to a special radius of velocity cancellation, which is called the turn-around radius. Measurements of the turn-around radius hold promises of constraining cosmological parameters, and possibly even properties of gravity. Such a measurement is, however, complicated by the fact that the surroundings of galaxy clusters are not spherical, but instead are a complicated collection of filaments, sheets and voids. In this paper we use the results of numerically simulated universes to quantify realistic error-bars of the measurement of the turn-around radius. We find that for a ΛCDM cosmology these error-bars are typically of the order of 20%. We numerically simulate three different implementations of dark energy models and of a scalar dark sector interaction to address whether the turn-around radius can be used to constrain non-trivial cosmologies, and we find that only rather extreme models can be distinguished from a ΛCDM universe due to the large error-bars arising from the non-trivial cluster environments.

cosmology
turn-around radius
galaxy cluster


The origin of cosmic rays: Explosions of massive stars with magnetic winds and their supernova mechanism

Abstract: One prediction of particle acceleration in the supernova remnants in the magnetic wind of exploding Wolf Rayet and Red Super Giant stars is that the final spectrum is a composition of a spectrum E^-7/3 and a polar cap component of E^-2 at the source. This polar cap component contributes to the total energy content with only a few percent, but dominates the spectrum at higher energy. The sum of both components gives spectra which curve upwards. The upturn was predicted to occur always at the same rigidity. An additional component of cosmic rays from acceleration by supernovae exploding into the Inter-Stellar Medium (ISM) adds another component for Hydrogen and for Helium. After transport the predicted spectra J(E) for the wind-SN cosmic rays are E^-8/3 and E^-7/3; the sum leads to an upturn from the steeper spectrum. An upturn has now been seen. Here, we test the observations against the predictions, and show that the observed properties are consistent with the predictions. Hydrogen can be shown to also have a noticeable wind-SN-component. The observation of the upturn in the heavy element spectra being compatible with the same rigidity for all heavy elements supports the magneto-rotational mechanism for these supernovae. This interpretation predicts the observed upturn to continue to curve upwards and approach the E^-7/3 spectrum. If confirmed, this would strengthen the case that supernovae of very massive stars with magnetic winds are important sources of Galactic cosmic rays.


Anisotropic Non-Gaussianity from a Two-Form Field

Abstract: We study an inflationary scenario with a two-form field to which an inflaton couples non-trivially. First, we show that anisotropic inflation can be realized as an attractor solution and that the two-form hair remains during inflation. A statistical anisotropy can be developed because of a cumulative anisotropic interaction induced by the background two-form field. The power spectrum of curvature perturbations has a prolate-type anisotropy, in contrast to the vector models having an oblate-type anisotropy. We also evaluate the bispectrum and trispectrum of curvature perturbations by employing the in-in formalism based on the interacting Hamiltonians. We find that the non-linear estimators f_NL and τ_NL are correlated with the amplitude g_* of the statistical anisotropy in the power spectrum. Unlike the vector models, both f_NL and τ_NL vanish in the squeezed limit. However, the estimator f_NL can reach the order of 10 in the equilateral and enfolded limits. These results are consistent with the latest bounds on f_NL constrained by Planck.

two-form field
anisotropic inflation
anisotropy
bispectrum
gauge field


Parametrizing theories of gravity on large and small scales in cosmology

Abstract: We present a link between parametrizations of alternative theories of gravity on large and small scales in cosmology. This relationship is established using theoretical consistency conditions only. We find that in both limits the "slip" and "effective Newton's constant" can be written in terms of a set of four functions of time, two of which are direct generalizations of the α and γ parameters from post-Newtonian physics. This generalizes previous work that has constructed frameworks for testing gravity on small scales, and is to the best of our knowledge the first time that a link between parametrizations of gravity on such very different scales has been established. We expect our result to facilitate the imposition of observational constraints, by drastically reducing the number of functional degrees of freedom required to consistently test gravity on multiple scales in cosmology.


Interstellar gamma rays and cosmic rays: new insights from Fermi-LAT AND INTEGRAL

Abstract: In over two years of operation Fermi-LAT has revolutionized our knowledge of the gamma-ray sky. Interstellar gamma rays are part of this new era and allow unprecedented tests for models of cosmic rays in the Galaxy. The extension to lower energies with INTEGRAL/SPI data is also evolving. The global multiwavelength luminosity of the Milky Way has been derived, with implications for the Galactic energy balance and the radio-FIR correlation.

cosmic ray
fermi-lat
interstellar gamma ray


The Mildly Non-Linear Regime of Structure Formation

Abstract: We present a simple physically motivated picture for the mildly non-linear regime of structure formation, which captures the effects of the bulk flows. We apply this picture to develop a method to significantly reduce the sample variance in cosmological N-body simulations at the scales relevant to the Baryon Acoustic Oscillations (BAO). The results presented in this paper will allow for a speed-up of an order of magnitude (or more) in the scanning of the cosmological parameter space using N-body simulations for studies which require a good handle of the mildly non-linear regime, such as those targeting the BAO. Using this physical picture we develop a simple formula, which allows for the rapid calculation of the mildly non-linear matter power spectrum to percent level accuracy, and for robust estimation of the BAO scale.

structure formation
sample variance
n-body simulation
perturbation theory
lpt


Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. IV. Relativistically Broadened Iron Lines

Abstract: According to the no-hair theorem, astrophysical black holes are fully characterized by their masses and spins and are described by the Kerr metric. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we calculate the profiles of fluorescent iron lines emitted from the accretion flows around black hole candidates within a framework that allows us to perform the calculation as a function of its mass and spin as well as of a free parameter that measures potential deviations from the Kerr metric. We show that such deviations lead to line profiles that are significantly altered and may exhibit a modified flux ratio of the two peaks in their characteristic double-peaked shape. We also show that the disk inclination can be measured independently of the spin and the deviation parameter at low to intermediate inclination angles as in the case of Kerr black holes. We estimate the precision that near-future X-ray missions such as Astro-H and ATHENA+ are required to achieve in order to resolve deviations from the Kerr metric in iron line profiles and show that constraints on such deviations will be strongest for rapidly spinning black holes. More generally, we show that measuring the line profile with a precision of 5 constraints the deviation parameter to order unity for values of the spin a>0.5M.

no-hair theorem
accretion disk
astrophysical model
electromagnetic radiation
x-ray reflection spectroscopy


Mapping the large-angle deviation from Gaussianity in simulated CMB maps

Abstract: [Abridged] In recent works we have proposed two new large-angle non-Gaussianity indicators based on skewness and kurtosis of patches of CMB sky-sphere, and used them to find out significant deviation from Gaussianity in frequency bands and foreground-reduced CMB maps. Simulated CMB maps with assigned type and amplitude of primordial non-Gaussianity are important tools to determine the strength, sensitivity and limitations of non-Gaussian estimators. Here we investigate whether and to what extent our non-Gaussian indicators have sensitivity to detect non-Gaussianity of local type, particularly with amplitude within the seven-year WMAP bounds. We make a systematic study by employing our statistical tools to generate maps of skewness and kurtosis from several thousands of simulated maps equipped with non-Gaussianity of local type of various amplitudes. We show that our indicators can be used to detect large-angle local-type non-Gaussianity only for relatively large values of the non-linear parameter f_ NL^ local. Thus, our indicators have not enough sensitivity to detect deviation from Gaussianity with the non-linear parameter within the seven-year WMAP bounds. This result along with the outcomes of frequency bands and foreground-reduced analyses suggest that non-Gaussianity captured in the previous works by our indicators is not of primordial origin, although it might have a primordial component. We have also made a comparative study of non-Gaussianity of simulated maps and of the full-sky WMAP foreground-reduced seven-year ILC-7yr map. An outcome of this analysis is that the level of non-Gaussianity of ILC-7yr map is higher than that of the simulated maps for f_ NL^ local within WMAP bounds. This provides quantitative indications on the suitability of the ILC-7yr map as a Gaussian reconstruction of the full-sky CMB.

gaussianity
cmb map
estimator
simulated map
spherical cell


TORUS-3DPDR: A self-consistent code treating three-dimensional photoionization and photodissociation regions

Abstract: The interaction of ionizing and far-ultraviolet radiation with the interstellar medium is of great importance. It results in the formation of regions in which the gas is ionized, beyond which are photodissociation regions (PDRs) in which the gas transitions to its atomic and molecular form. Several numerical codes have been implemented to study these two main phases of the interstellar medium either dynamically or chemically. In this paper we present TORUS-3DPDR, a new self-consistent code for treating the chemistry of three-dimensional photoionization and photodissociation regions. It is an integrated code coupling the two codes TORUS, a hydrodynamics and Monte Carlo radiation transport code, and 3D-PDR, a photodissociation regions code. The new code uses a Monte Carlo radiative transfer scheme to account for the propagation of the ionizing radiation including the diffusive component as well as a ray-tracing scheme based on the HEALPix package in order to account for the escape probability and column density calculations. Here, we present the numerical techniques we followed and we show the capabilities of the new code in modelling three-dimensional objects including single or multiple sources. We discuss the effects introduced by the diffusive component of the UV field in determining the thermal balance of PDRs as well as the effects introduced by a multiple sources treatment of the radiation field. We find that diffuse radiation can positively contribute to the formation of CO. With this new code, three-dimensional synthetic observations for the major cooling lines are possible, for making feasible a detailed comparison between hydrodynamical simulations and observations.

three-dimensional photoionization
photodissociation region
torus-3dpdr


Model-independent Curvature Determination from Gravitational-Wave Standard Sirens and Cosmic Chronometers

Abstract: The detection of gravitational waves (GWs) provides a direct way to measure the luminosity distance, which enables us to probe cosmology. In this paper, we continue to expand the application of GW standard sirens in cosmology, and propose that the spatial curvature can be estimated in a model-independent way by comparing the distances from future GW sources and current cosmic-chronometer observations. We expect an electromagnetic counterpart of the GW event to give the source redshift, and simulate hundreds of GW data from the coalescence of double neutron stars and black hole–neutron star binaries using the Einstein Telescope as reference. Our simulations show that, from 100 simulated GW events and 31 current cosmic-chronometer measurements, the error of the curvature parameter Ω_K is expected to be constrained at the level of ∼0.125. If 1000 GW events are observed, the uncertainty of Ω_K would be further reduced to ∼0.040. We also find that adding 50 mock H(z) data (consisting of 81 cosmic-chronometer data and 1000 simulated GW events) could result in much tighter constraint on the zero cosmic curvature, for which, Ω_K=-0.002±0.028. Compared to some actual model-independent curvature tests involving the distances from other cosmic probes, this method with GW data achieves constraints with much higher precision.

gravitational wave
cosmology
spatial curvature


Measuring Supermassive Black Hole Spins in Active Galactic Nuclei

Abstract: Measuring the spins of supermassive black holes (SMBHs) in active galactic nuclei (AGN) can inform us about the relative role of gas accretion vs. mergers in recent epochs of the life of the host galaxy and its AGN. Recent advances in theory and observation have enabled spin measurements for a handful of SMBHs thus far, but this science is still very much in its infancy. Herein, I discuss how and why we seek to measure black hole spin in AGN, using recent results from long X-ray observing campaigns on three radio-quiet AGN (MCG-6-30-15, NGC 3783 and Fairall 9) to illustrate this process and its caveats. I then present our current knowledge of the distribution of SMBH spins in the local universe. I also address prospects for improving the accuracy, precision and quantity of these spin constraints in the next decade and beyond with instruments such as NuSTAR, Astro-H and a future generation large-area X-ray telescope.

black hole
hole spin
accretion disk
active galactic nucleus


A Living Theory Catalogue for Fast Radio Bursts

Abstract: At present, we have almost as many theories to explain Fast Radio Bursts as we have Fast Radio Bursts observed. This landscape will be changing rapidly with CHIME/FRB, recently commissioned in Canada, and HIRAX, under construction in South Africa. This is an opportune time to review existing theories and their observational consequences, allowing us to efficiently curtail viable astrophysical models as more data becomes available. In this article we provide a currently up to date catalogue of the numerous and varied theories proposed for Fast Radio Bursts so far. We also launch an online evolving repository for the use and benefit of the community to dynamically update our theoretical knowledge and discuss constraints and uses of Fast Radio Bursts.

fast radio bursts
frb
date
compact object


Tree-Level Bispectrum in the Effective Field Theory of Large-Scale Structure extended to Massive Neutrinos

Abstract: We compute the tree-level bispectrum of dark matter in the presence of massive neutrinos in the mildly non-linear regime in the context of the effective field theory of large-scale structure (EFTofLSS). For neutrinos, whose typical free streaming wavenumber (k_ fs) is longer than the non-linear scale (k_NL), we solve a Boltzmann equation coupled to the effective fluid equation for dark matter. We solve perturbatively the coupled system by expanding in powers of the neutrino density fraction (f_ν) and the ratio of the wavenumber of interest over the non-linear scale (k/k_NL) and add suitable counterterms to remove the dependence from short distance physics. For equilateral configurations, we find that the total-matter tree-level bispectrum is approximately 16f_ν times the dark matter one on short scales (k > k_ fs). The largest contribution stems from the back-reaction of massive neutrinos on the dark matter growth factor. On large scales (k < k_ fs) the contribution of neutrinos to the bispectrum is smaller by up to two orders of magnitude.

effective field theory
neutrino
tree-level bispectrum


Quantifying the non-Gaussianity in the EoR 21-cm signal through bispectrum

Abstract: The epoch of reionization (EoR) 21-cm signal is expected to be highly non-Gaussian in nature and this non-Gaussianity is also expected to evolve with the progressing state of reionization. Therefore the signal will be correlated between different Fourier modes (k). The power spectrum will not be able capture this correlation in the signal. We use a higher-order estimator – the bispectrum – to quantify this evolving non-Gaussianity. We study the bispectrum using an ensemble of simulated 21-cm signal and with a large variety of k triangles. We observe two competing sources driving the non-Gaussianity in the signal: fluctuations in the neutral fraction (x_ HI) field and fluctuations in the matter density field. We find that the non-Gaussian contribution from these two sources vary, depending on the stage of reionization and on which k modes are being studied. We show that the sign of the bispectrum works as a unique marker to identify which among these two components is driving the non-Gaussianity. We propose that the sign change in the bispectrum, when plotted as a function of triangle configuration cosθ and at a certain stage of the EoR can be used as a confirmative test for the detection of the 21-cm signal. We also propose a new consolidated way to visualize the signal evolution (with evolving x_ HI or redshift), through the trajectories of the signal in a power spectrum and equilateral bispectrum i.e. P(k)-B(k, k, k) space.

non-gaussianity
eor 21-cm signal
bispectrum


Abstract: The Diffuse Supernova Neutrino Background (DSNB) is the weak glow of MeV neutrinos and antineutrinos from distant core-collapse supernovae. The DSNB has not been detected yet, but the Super-Kamiokande (SK) 2003 upper limit on the electron antineutrino flux is close to predictions, now quite precise, based on astrophysical data. If SK is modified with dissolved gadolinium to reduce detector backgrounds and increase the energy range for analysis, then it should detect the DSNB at a rate of a few events per year, providing a new probe of supernova neutrino emission and the cosmic core-collapse rate. If the DSNB is not detected, then new physics will be required. Neutrino astronomy, while uniquely powerful, has proven extremely difficult – only the Sun and the nearby Supernova 1987A have been detected to date – so the promise of detecting new sources soon is exciting indeed.

neutrino
distant core-collapse supernovae
star-formation rate


Large anisotropies of the stochastic gravitational wave background from cosmic domain walls

Abstract: We investigate the stochastic gravitational wave background (SGWB) from cosmic domain walls (DWs) caused by quantum fluctuations of a light scalar field ϕ during inflation. Perturbations of ϕ remain almost constant after leaving the Hubble horizon. The probabilities of the two domains depend on the averaged value of ϕ at each large scale region, leading to large scale perturbations of DW energy density and large anisotropies in the SGWB. We find that the angular power spectrum is scale-invariant and at least of the order of 10^-2, which is expected to be detected by future gravitational-wave (GW) detectors. Since we have not detected primordial GWs yet, anisotropies of the SGWB could help us to verify the rationality of inflation and determine the energy scale of inflation.

gravitational wave background
cosmic domain wall
large anisotropy


Kinematic dipole detection with galaxy surveys: forecasts and requirements

Abstract: Upcoming or future deep galaxy samples with wide sky coverage can provide independent measurement of the kinematic dipole - our motion relative to the rest frame defined by the large-scale structure. Such a measurement would present an important test of the standard cosmological model, as the standard model predicts the galaxy measurement should precisely agree with the existing precise measurements made using the CMB. However, the required statistical precision to measure the kinematic dipole typically makes the measurement susceptible to bias from the presence of the local-structure-induced dipole contamination. In order to minimize the latter, a sufficiently deep survey is required. We forecast both the statistical error and the systematic bias in the kinematic dipole measurements. We find that a survey covering ∼ 75% of the sky in both hemispheres and having ∼ 30 million galaxies can detect the kinematic dipole at 5σ, while its median redshift should be at least z_med∼ 0.75 for negligible bias from the local structure.


The second flight of the SUNRISE balloon-borne solar observatory: overview of instrument updates, the flight, the data and first results

Abstract: The SUNRISE balloon-borne solar observatory, consisting of a 1 m aperture telescope that provided a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in June 2013. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg ii k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000 Å after Multi-Frame Blind Deconvolution reconstruction accounting for phase-diversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR 11768 observed relatively close to disk centre is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500 G and, while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere.

second flight
sunrise
balloon-borne solar observatory


Velocity filtration and temperature inversion in a system with long-range interactions

Abstract: Temperature inversion due to velocity filtration, a mechanism originally proposed to explain the heating of the solar corona, is demonstrated to occur also in a simple paradigmatic model with long-range interactions, the Hamiltonian mean-field model. Using molecular dynamics simulations, we show that when the system settles into an inhomogeneous quasi-stationary state in which the velocity distribution has suprathermal tails, the temperature and density profiles are anticorrelated: denser parts of the system are colder than dilute ones. We argue that this may be a generic property of long-range interacting systems.

temperature inversion
long-range interaction
velocity filtration


Jeans analysis in modified gravity

Abstract: MOdified Gravity (MOG) is a covariant modification of Einstein's general relativity. This theory is one of the current alternatives to dark matter models. We describe dynamics of collisionless self-gravitating systems in the context of MOG. By studying the weak field approximation of this theory, we derive the equations governing the dynamics of the self-gravitating systems. More specifically, we consider the Jeans instability for self-gravitating fluid and stellar systems, and derive new Jeans mass limit M̃_J and wave-number k̃_J. Furthermore, considering the gravitational instability in star forming regions, we show that MOG has not a significant difference with general relativity on this astrophysical scale. However, at larger scales such as intergalactic space MOG may lead to different galaxy and structure formation processes.

mog
galaxy
rotation curve
scalar-tensor-vector-gravity


Is there evidence for anomalous dipole anisotropy in the large-scale structure?

Abstract: We probe the anisotropy of the large-scale structure (LSS) with the WISE-2MASS catalogue. This analysis is performed by a directional comparison of the galaxy number counts through the entire celestial sphere once systematic effects, such as star-galaxy separation and foregrounds contamination, are properly taken into account. We find a maximal hemispherical asymmetry whose dipolar component is A = 0.0507 ± 0.0014 toward the (l,b) = (323^∘,-5^∘) direction, whose result is consistent with previous estimations of our proper motion in low and intermediate redshifts, as those carried out with Type Ia Supernovae and similar LSS catalogues. Furthermore, this dipole amplitude is statistically consistent (p-value = 0.061) with mock catalogues simulated according to the expected ΛCDM matter density fluctuations, in addition to observational biases such as the incomplete celestial coverage and anisotropic sky exposure. Our results suggest, therefore, that there is no strong evidence for anomalous anisotropy in the LSS, given the limitations and systematics of current data, in the concordance model scenario.

dipole anisotropy
large-scale structure
redshift


CMB-S4 Technology Book, First Edition

Abstract: CMB-S4 is a proposed experiment to map the polarization of the Cosmic Microwave Background (CMB) to nearly the cosmic variance limit for angular scales that are accessible from the ground. The science goals and capabilities of CMB-S4 in illuminating cosmic inflation, measuring the sum of neutrino masses, searching for relativistic relics in the early universe, characterizing dark energy and dark matter, and mapping the matter distribution in the universe have been described in the CMB-S4 Science Book. This Technology Book is a companion volume to the Science Book. The ambitious science goals of CMB-S4, a "Stage-4" experiment, require a step forward in experimental capability from the current Stage=II experiments. To guide this process, we summarize the current state of CMB instrumentation technology, and identify R D efforts necessary to advance it for use in CMB-S4. The book focuses on technical challenges in four broad areas: Telescope Design; Receiver Optics; Focal-Plane Optical Coupling; and Focal-Plane Sensor and Readout.


Coarse-Grained Cosmological Perturbation Theory

Abstract: Semi-analytical methods, based on Eulerian perturbation theory, are a promising tool to follow the time evolution of cosmological perturbations at small redshifts and at mildly nonlinear scales. All these schemes are based on two approximations: the existence of a smoothing scale and the single-stream approximation, where velocity dispersion of the dark matter fluid, as well as higher moments of the particle distributions, are neglected. Despite being widely recognized, these two assumptions are, in principle, incompatible, since any finite smoothing scale gives rise to velocity dispersion and higher moments at larger scales. We describe a new approach to perturbation theory, where the Vlasov and fluid equations are derived in presence of a finite coarse-graining scale: this allows a clear separation between long and short distance modes and leads to a hybrid approach where the former are treated perturbatively and the effect of the latter is encoded in external source terms for velocity, velocity dispersion, and all the higher order moments, which can be computed from N-body simulations. We apply the coarse-grained perturbation theory to the computation of the power spectrum and the cross-spectrum between density and velocity dispersion, and compare the results with N-body simulations, finding good agreement.

cosmological perturbation theory
scheme
single-stream approximation
length scale


Supersymmetry, Nonthermal Dark Matter and Precision Cosmology

Abstract: Within the Minimal Supersymmetric Standard Model (MSSM), LHC bounds suggest that scalar superpartner masses are far above the electroweak scale. Given a high superpartner mass, nonthermal dark matter is a viable alternative to WIMP dark matter generated via freezeout. In the presence of moduli fields nonthermal dark matter production is associated with a long matter dominated phase, modifying the spectral index and primordial tensor amplitude relative to those in a thermalized primordial universe. Nonthermal dark matter can have a higher self-interaction cross-section than its thermal counterpart, enhancing astrophysical bounds on its annihilation signals. We constrain the contributions to the neutralino mass from the bino, wino and higgsino using existing astrophysical bounds and direct detection experiments for models with nonthermal neutralino dark matter. Using these constraints we quantify the expected change to inflationary observables resulting from the nonthermal phase.

nonthermal dark matter
precision cosmology
supersymmetry


Speed of Gravitational Waves and the Fate of Scalar-Tensor Gravity

Abstract: The direct detection of gravitational waves (GWs) is an invaluable new tool to probe gravity and the nature of cosmic acceleration. A large class of scalar-tensor theories predict that GWs propagate with velocity different than the speed of light, a difference that can be 𝒪(1) for many models of dark energy. We determine the conditions behind the anomalous GW speed, namely that the scalar field spontaneously breaks Lorentz invariance and couples to the metric perturbations via the Weyl tensor. If these conditions are realized in nature, the delay between GW and electromagnetic (EM) signals from distant events will run beyond human timescales, making it impossible to measure the speed of GWs using neutron star mergers or other violent events. We present a robust strategy to exclude or confirm an anomalous speed of GWs using eclipsing binary systems, whose EM phase can be exquisitely determined. he white dwarf binary J0651+2844 is a known example of such system that can be used to probe deviations in the GW speed as small as c_g/c-1≳ 2· 10^-12 when LISA comes online. This test will either eliminate many contender models for cosmic acceleration or wreck a fundamental pillar of general relativity.

gravity
scalar-tensor theory
propagation
dark energy


ALMA Census of Faint 1.2 mm Sources Down to 0.02 mJy: Extragalactic Background Light and Dust-Poor High-z Galaxies

Abstract: We present statistics of 133 faint 1.2-mm continuum sources detected in about 120 deep ALMA pointing data that include all the archival deep data available by 2015 June. We derive number counts of 1.2 mm continuum sources down to 0.02 mJy partly with the assistance of gravitational lensing, and find that the total integrated 1.2 mm flux of the securely identified sources is 22.9^(+6.7)_(-5.6) Jy deg^(-2) that corresponds to 104^(+31)_(-25) extragalactic background light (EBL) measured by COBE observations. These results suggest that the major 1.2 mm EBL contributors are sources with 0.02 mJy, and that very faint 1.2 mm sources with < 0.02 mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias bg by the counts-in-cells technique, and place a stringent upper limit of bg < 3.5 that is not similar to bg values of massive DRGs and SMGs but comparable to those of UV-bright sBzKs and LBGs. Moreover, in optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59 have luminosities, colors, and the IRX-beta relation same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.

faint
extragalactic background light
dust-poor high-z galaxy


Detecting higher spin fields through statistical anisotropy in the CMB and galaxy power spectra

Abstract: Primordial inflation may represent the most powerful collider to test high-energy physics models. In this paper we study the impact on the inflationary power spectrum of the comoving curvature perturbation in the specific model where massive higher spin fields are rendered effectively massless during a de Sitter epoch through suitable couplings to the inflaton field. In particular, we show that such fields with spin s induce a distinctive statistical anisotropic signal on the power spectrum, in such a way that not only the usual g_2M-statistical anisotropy coefficients, but also higher-order ones (i.e., g_4M, g_6M, ⋯, g_(2s-2)M and g_(2s) M) are nonvanishing. We examine their imprints in the cosmic microwave background and galaxy power spectra. Our Fisher matrix forecasts indicate that the detectability of g_LM depends very weakly on L: all coefficients could be detected in near future if their magnitudes are bigger than about 10^-3.

galaxy power spectra
curvature perturbation
high spin field


CoGeNT Interpretations

Abstract: Recently, the CoGeNT experiment has reported events in excess of expected background. We analyze dark matter scenarios which can potentially explain this signal. Under the standard case of spin independent scattering with equal couplings to protons and neutrons, we find significant tensions with existing constraints. Consistency with these limits is possible if a large fraction of the putative signal events is coming from an additional source of experimental background. In this case, dark matter recoils cannot be said to explain the excess, but are consistent with it. We also investigate modifications to dark matter scattering that can evade the null experiments. In particular, we explore generalized spin independent couplings to protons and neutrons, spin dependent couplings, momentum dependent scattering, and inelastic interactions. We find that some of these generalizations can explain most of the CoGeNT events without violation of other constraints. Generalized couplings with some momentum dependence, allows further consistency with the DAMA modulation signal, realizing a scenario where both CoGeNT and DAMA signals are coming from dark matter. A model with dark matter interacting and annihilating into a new light boson can realize most of the scenarios considered.

proton
matter interaction
cogent
cross section
gev


The status of varying constants: a review of the physics, searches and implications

Abstract: The observational evidence for the recent acceleration of the universe demonstrates that canonical theories of cosmology and particle physics are incomplete—if not incorrect—and that new physics is out there, waiting to be discovered. A key task for the next generation of laboratory and astrophysical facilities is to search for, identify and ultimately characterize this new physics. Here we highlight recent developments in tests of the stability of nature's fundamental couplings, which provide a direct handle on new physics: a detection of variations will be revolutionary, but even improved null results provide competitive constraints on a range of cosmological and particle physics paradigms. A joint analysis of all currently available data shows a preference for variations of α and μ at about the two-sigma level, but inconsistencies between different sub-sets (likely due to hidden systematics) suggest that these statistical preferences need to be taken with caution. On the other hand, these measurements strongly constrain Weak Equivalence Principle violations. Plans and forecasts for forthcoming studies with facilities such as ALMA, ESPRESSO and the ELT, which should clarify these issues, are also discussed, and synergies with other probes are briefly highlighted. The goal is to show how a new generation of precision consistency tests of the standard paradigm will soon become possible.

status
universe
stability
fundamental coupling
fine-structure constant


Cosmological long-wavelength solutions and primordial black hole formation

Abstract: We construct cosmological long-wavelength solutions without symmetry in general gauge conditions compatible with the long-wavelength scheme. We then specify the relationship among the solutions in different time slicings. Applying this general framework to spherical symmetry, we derive the correspondence relation between long-wavelength solutions in the constant mean curvature slicing with conformally flat spatial coordinates and asymptotic quasihomogeneous solutions in the comoving gauge and compare the numerical results of PBH formation in these two different approaches. To discuss the PBH formation, it is convenient and conventional to use δ̃_c, the value which the averaged density perturbation at threshold in the comoving slicing would take at horizon entry in the lowest-order long-wavelength expansion. We numerically find that within compensated models, the sharper the transition from the overdense region to the FRW universe is, the larger the δ̃_c becomes. We suggest that, for the equation of state p=(Γ-1)ρ, we can apply the analytic formulas for the minimum δ̃_c, min≃ [3Γ/(3Γ+2)]sin^2[π√(Γ-1)/(3Γ-2)] and the maximum δ̃_c, max≃ 3Γ/(3Γ+2). As for the threshold peak value of the curvature variable ψ_0,c, we find that the sharper the transition is, the smaller the ψ_0,c becomes. We analytically explain this feature. Using simplified models, we also analytically deduce an environmental effect that ψ_0,c can be significantly larger (smaller) if the underlying density perturbation of much longer wavelength is positive (negative).

gauge condition
density perturbation
comoving slicing
universe
cosmological long-wavelength solution


Resummed Kinetic Field Theory: Using Mesoscopic Particle Hydrodynamics to Describe Baryonic Matter in a Cosmological Framework

Abstract: Recently, Bartelmann et al. presented a 'Kinetic Field Theory' (KFT) formalism to tackle the difficulties of large scale structure formation. In this approach, the dynamics of a non-equilibrium ensemble of classical particles are examined based on methods of statistical field theory. So far, only contributions coming from dark matter were considered, which is assumed to pose an accurate description of our universe on very large scales. Nevertheless, going to smaller scales, also baryonic contributions have to be taken into account. Building on the ideas of Viermann et al. we present an effective particle model of hydrodynamics to describe baryonic matter in a cosmological framework. Using this model, the baryonic density contrast power spectrum is computed to lowest perturbative order within the resummed KFT framework of Lilow et al. We discuss the qualitative differences to the dark matter case and perform a quantitative comparison to the baryonic spectrum obtained from Eulerian perturbation theory. A subsequent paper will resolve the problem of coupling both theories describing dark and baryonic matter, respectively, to gain a full model of cosmic matter. Even though our focus is on cosmological systems only, we want to emphasize that all methods presented here are of a quite general fashion, making it applicable also to other fields.

mesoscopic particle hydrodynamics
baryonic matter
cosmological framework


Can thermal inflation be consistent with baryogenesis in gauge-mediated SUSY breaking models?

Abstract: Thermal inflation is an attractive idea to dilute cosmic density of unwanted particles such as moduli fields which cause cosmological difficulties. However, it also dilutes preexisting baryon asymmetry and some viable baryogenesis is necessary for a cosmologically consistent scenario. We investigate whether the Affleck-Dine mechanism can produce baryon asymmetry enough to survive after the dilution in gauge-mediated SUSY breaking models. Flat directions except for LH_u flat direction cannot provide such huge baryon number because of Q-ball formation. We show that although the LH_u flat direction is special in terms of having μ-term which prevents Q-ball formation, it cannot explain the observed baryon asymmetry either.

thermal inflation
baryogenesis
susy breaking model


Examining subgrid models of supermassive black holes in cosmological simulation

Abstract: While supermassive black holes (SMBHs) play an important role in galaxy and cluster evolution, at present they can only be included in large-scale cosmological simulation via subgrid techniques. However, these subgrid models have not been studied in a systematic fashion. Using a newly-developed fast, parallel spherical overdensity halo finder built into the simulation code FLASH, we perform a suite of dark matter-only cosmological simulations to study the effects of subgrid model choice on relations between SMBH mass and dark matter halo mass and velocity dispersion. We examine three aspects of SMBH subgrid models: the choice of initial black hole seed mass, the test for merging two black holes, and the frequency of applying the subgrid model. We also examine the role that merging can play in determining the relations, ignoring the complicating effects of SMBH-driven accretion and feedback. We find that the choice of subgrid model can dramatically affect the black hole merger rate, the cosmic SMBH mass density, and the low-redshift relations to halo properties. We also find that it is possible to reproduce observations of the low-redshift relations without accretion and feedback, depending on the choice of subgrid model.

subgrid model
supermassive black hole
cosmological simulation


Geodesic completeness and homogeneity condition for cosmic inflation

Abstract: There are two disjointed problems in cosmology within General Relativity (GR), which can be addressed simultaneously by studying the nature of geodesics around t→ 0, where t is the physical time. One is related to the past geodesic completeness of the inflationary trajectory due to the presence of a cosmological singularity, and the other one is related to the homogeneity condition required to inflate a local space-time patch of the universe. We will show that both the problems have a common origin, arising from how the causal structure of null and timelike geodesics are structured within GR. In particular, we will show how a non-local extension of GR can address both problems, while satisfying the null energy condition for the matter sources.

homogeneity condition
cosmological singularity
geodesic completeness


Consistency relations for sharp features in the primordial spectra

Abstract: We study the generation of sharp features in the primordial spectra within the framework of effective field theory of inflation, wherein curvature perturbations are the consequence of the dynamics of a single scalar degree of freedom. We identify two sources in the generation of features: rapid variations of the sound speed c_s (at which curvature fluctuations propagate) and rapid variations of the expansion rate H during inflation. With this in mind, we propose a non-trivial relation linking these two quantities that allows us to study the generation of sharp features in realistic scenarios where features are the result of the simultaneous occurrence of these two sources. This relation depends on a single parameter with a value determined by the particular model (and its numerical input) responsible for the rapidly varying background. As a consequence, we find a one-parameter consistency relation between the shape and size of features in the bispectrum and features in the power spectrum. To substantiate this result, we discuss several examples of models for which this one-parameter relation (between c_s and H) holds, including models in which features in the spectra are both sudden and resonant.

sharp feature
primordial spectra
consistency relation


Non-Gaussianity Consistency Relations, Initial States and Back-reaction

Abstract: We explore the consistency relations for the three-point functions, in the squeezed limit, of scalar and tensor perturbations in single-field inflation with general initial conditions for the perturbations. For slow-roll inflation, we find that all the three-point functions of scalar and tensor perturbations with a coherent state as the initial state are identical to the three-point functions with the Bunch-Davies initial state. On the other hand, there is an apparent violation of some of the consistency relations for initial states that are related to the Bunch-Davies state by Bogoliubov transformations and we identify the reason for this violation. The back-reaction calculations indicate that the three-point functions for these states can be large enough to violate the consistency relations, however, they are too small to be observed in the near future.

consistency relation
initial state
three-point function
tensor perturbation


The frequency of very young galaxies in the local Universe: I. A test for galaxy formation and cosmological models

Abstract: In the local Universe, the existence of very young galaxies (VYGs), having formed at least half their stellar mass in the last 1 Gyr, is debated. We predict the present-day fraction of VYGs among central galaxies as a function of galaxy stellar mass. For this, we apply to high mass resolution Monte-Carlo halo merger trees (MCHMTs) three (one) analytical models of galaxy formation, where the ratio of stellar to halo mass (mass growth rate) is a function of halo mass and redshift. Galaxy merging is delayed until orbital decay by dynamical friction. With starbursts associated with halo mergers, our models predict typically one percent of VYGs up to galaxy masses of 10^10 M_⊙, falling rapidly at higher masses, and VYGs are usually associated with recent major mergers of their haloes. Without these starbursts, two of the models have VYG fractions reduced by 1 or 2 dex at low or intermediate stellar masses, and VYGs are rarely associated with major halo mergers. In comparison, the state-of-the-art semi-analytical model (SAM) of Henriques et al. produces only 0.01 MCMHTs with Warm Dark Matter cosmology generates 10 times more VYGs at masses below 10^8 M_⊙ than when run with Cold Dark Matter. The wide range in these VYG fractions illustrates the usefulness of VYGs to constrain both galaxy formation and cosmological models.

local universe
galaxy formation
cosmological model


New Parametrization for the Scale Dependent Growth Function in General Relativity

Abstract: We demonstrate the scale dependence of the growth function of cosmological perturbations in dark energy models based on General Relativity. This scale dependence is more prominent on cosmological scales of 100h^-1Mpc or larger. We derive a new scale dependent parametrization which generalizes the well known Newtonian approximation result f_0(a)≡dlnδ_0/dln a=(a)^γ (γ =6/11 for ) which is a good approximation on scales less than 50h^-1Mpc. Our generalized parametrization is of the form f(a)=f_0(a)/1+ξ(a,k) where ξ(a,k)=3 H_0^2/a k^2. We demonstrate that this parametrization fits the exact result of a full general relativistic evaluation of the growth function up to horizon scales for both and dynamical dark energy. In contrast, the scale independent parametrization does not provide a good fit on scales beyond 5

parametrization
growth function
general relativity


Power-law modulation of the scalar power spectrum from a heavy field with a monomial potential

Abstract: The effects of heavy fields modulate the scalar power spectrum during inflation. We analytically calculate the modulations of the scalar power spectrum from a heavy field with a separable monomial potential, i.e. V(ϕ) ϕ^n. In general the modulation is characterized by a power-law oscillation which is reduced to the logarithmic oscillation in the case of n=2.

scalar power
heavy field
monomial potential


Topological Currents in Neutron Stars: Kicks, Precession, Toroidal Fields, and Magnetic Helicity

Abstract: The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and P-parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics – they are all P-odd phenomena that stem from a topological current generated by parity violation.

neutron star
magnetic helicity
toroidal magnetic field


Fast radio bursts' recipes for the distributions of dispersion measures, flux densities, and fluences

Abstract: We investigate how the statistical properties of dispersion measure (DM) and apparent flux density/fluence of (non-repeating) fast radio bursts (FRBs) are determined by unknown cosmic rate density history [(z)] and luminosity function (LF) of the transient events. We predict the distributions of DMs, flux densities, and fluences of FRBs taking account of the variation of the receiver efficiency within its beam, using analytical models of (z) and LF. Comparing the predictions with the observations, we show that the cumulative distribution of apparent fluences suggests that FRBs originate at cosmological distances and increases with redshift resembling cosmic star formation history (CSFH). We also show that a LF model with a bright-end cutoff at log_10L_ν [erg s^-1Hz^-1] ∼ 34 are favored to reproduce the observed DM distribution if (z)∝ CSFH, although the statistical significance of the constraints obtained with the current size of the observed sample is not high. Finally, we find that the correlation between DM and flux density of FRBs is potentially a powerful tool to distinguish whether FRBs are at cosmological distances or in the local universe more robustly with future observations.

dispersion measure
flux density
fast radio burst


Discontinuous Galerkin methods for general-relativistic hydrodynamics: formulation and application to spherically symmetric spacetimes

Abstract: We have developed the formalism necessary to employ the discontinuous-Galerkin approach in general-relativistic hydrodynamics. The formalism is firstly presented in a general 4-dimensional setting and then specialized to the case of spherical symmetry within a 3+1 splitting of spacetime. As a direct application, we have constructed a one-dimensional code, EDGES, which has been used to asses the viability of these methods via a series of tests involving highly relativistic flows in strong gravity. Our results show that discontinuous Galerkin methods are able not only to handle strong relativistic shock waves but, at the same time, to attain very high orders of accuracy and exponential convergence rates in smooth regions of the flow. Given these promising prospects and their affinity with a pseudospectral solution of the Einstein equations, discontinuous Galerkin methods could represent a new paradigm for the accurate numerical modelling in relativistic astrophysics.

general-relativistic hydrodynamic
spacetime
discontinuous galerkin method


Energy source for the magnetic field growth in magnetars driven by the electron-nucleon interaction

Abstract: We study the magnetic field generation in a neutron star within the model based on the magnetic field instability in the nuclear matter owing to the electron-nucleon parity violating interaction. We suggest that the growing magnetic field takes the energy from thermal background fermions in the neutron star matter. The system of kinetic equations for the spectra of the magnetic helicity density and magnetic energy density as well as the chiral imbalance are solved numerically accounting for this energy source. We obtain that, for the initial conditions corresponding to a typical neutron star, the large scale magnetic field ∼ 10^15G is generated during (10^4-10^5)yr. We suggest that the proposed model describes strong magnetic fields observed in magnetars.

magnetic field
electron-nucleon interaction
field instability


Finite escape fraction for ultrahigh energy collisions around Kerr naked singularity

Abstract: We investigate here the issue of observability of high energy collisions around Kerr naked singu- larity and show that the results are in contrast with the Kerr black hole case. We had shown earlier that it would be possible to have ultrahigh energy collisions between the particles close to the loca- tion r = M around the Kerr naked singularity if the Kerr spin parameter transcends the unity by an infinitesimally small amount a → 1^+. The collision is between initially ingoing particle that turns back as an outgoing particle due to angular momentum barrier, with another ingoing particle. We assume that two massless particles are produced in such a collision and their angular distribution is isotropic in the center of mass frame. We calculate the escape fraction for the massless particles to reach infinity. We show that escape fraction is finite and approximately equal to half for ultrahigh energy collisions. Therefore the particles produced in high energy collisions would escape to infinity providing signature of the nature of basic interactions at those energies. This result is in contract with the extremal Kerr black hole case where almost all particles produced in high energy collisions are absorbed by the black hole, thus rendering the collisions unobservable.

escape fraction
ultrahigh energy collision
singularity


Structure formation from non-Gaussian initial conditions: multivariate biasing, statistics, and comparison with N-body simulations

Abstract: We study structure formation in the presence of primordial non-Gaussianity of the local type with parameters f_NL and g_NL. We show that the distribution of dark-matter halos is naturally described by a multivariate bias scheme where the halo overdensity depends not only on the underlying matter density fluctuation delta, but also on the Gaussian part of the primordial gravitational potential phi. This corresponds to a non-local bias scheme in terms of delta only. We derive the coefficients of the bias expansion as a function of the halo mass by applying the peak-background split to common parametrizations for the halo mass function in the non-Gaussian scenario. We then compute the halo power spectrum and halo-matter cross spectrum in the framework of Eulerian perturbation theory up to third order. Comparing our results against N-body simulations, we find that our model accurately describes the numerical data for wavenumbers k < 0.1-0.3 h/Mpc depending on redshift and halo mass. In our multivariate approach, perturbations in the halo counts trace phi on large scales and this explains why the halo and matter power spectra show different asymptotic trends for k -> 0. This strongly scale-dependent bias originates from terms at leading order in our expansion. This is different from what happens using the standard univariate local bias where the scale-dependent terms come from badly behaved higher-order corrections. On the other hand, our biasing scheme reduces to the usual local bias on smaller scales where |phi| is typically much smaller than the density perturbations. We finally discuss the halo bispectrum in the context of multivariate biasing and show that, due to its strong scale and shape dependence, it is a powerful tool for the detection of primordial non-Gaussianity from future galaxy surveys.

multivariate biasing
n-body simulation
structure formation


D-Foam Phenomenology: Dark Energy, the Velocity of Light and a Possible D-Void

Abstract: In a D-brane model of space-time foam, there are contributions to the dark energy that depend on the D-brane velocities and on the density of D-particle defects. The latter may also reduce the speeds of photons linearly with their energies, establishing a phenomenological connection with astrophysical probes of the universality of the velocity of light. Specifically, the cosmological dark energy density measured at the present epoch may be linked to the apparent retardation of energetic photons propagating from nearby AGNs. However, this nascent field of `D-foam phenomenology' may be complicated by a dependence of the D-particle density on the cosmological epoch. A reduced density of D-particles at redshifts z 1 - a `D-void' - would increase the dark energy while suppressing the vacuum refractive index, and thereby might reconcile the AGN measurements with the relatively small retardation seen for the energetic photons propagating from GRB 090510, as measured by the Fermi satellite.


On stars, galaxies and black holes in massive bigravity

Abstract: In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for the existence of viable star solutions when the radius of the star is much smaller than the Compton wavelength of the graviton. If these parameter conditions are not met, we constrain the ratio between the coupling constants of the two metrics, in order to give viable conditions for e.g. neutron stars. For galaxies, we put constraints on both the Compton wavelength of the graviton and the conformal factor and coupling constants of the two metrics. The relationship between black holes and stars, and whether the former can be formed from the latter, is discussed. We argue that the different asymptotic structure of stars and black holes makes it unlikely that black holes form from the gravitational collapse of stars in massive bigravity.


Model-independent estimations for the curvature from standard candles and clocks

Abstract: Model-independent estimations for the spatial curvature not only provide a test for the fundamental Copernican principle assumption, but also can effectively break the degeneracy between curvature and dark energy properties. In this paper, we propose to achieve model-independent constraints on the spatial curvature from observations of standard candles and standard clocks, without assuming any fiducial cosmology and other priors. We find that, for the popular Union2.1 type Ia supernovae (SNe Ia ) observations, the spatial curvature is constrained to be Ω_K=-0.045_-0.172^+0.176. For the latest joint light-curve analysis (JLA) of SNe Ia observations, we obtain Ω_K=-0.140_-0.158^+0.161. It is suggested that these results are in excellent agreement with the spatially flat Universe. Moreover, compared to other approaches aiming for model-independent estimations of spatial curvature, this method also achieves constraints with competitive precision.

curvature
clock
model-independent estimation


Higher-derivative operators and effective field theory for general scalar-tensor theories

Abstract: We discuss the extent to which it is necessary to include higher-derivative operators in the effective field theory of general scalar-tensor theories. We explore the circumstances under which it is correct to restrict to second-order operators only, and demonstrate this using several different techniques, such as reduction of order and explicit field redefinitions. These methods are applied, in particular, to the much-studied Horndeski theories. The goal is to clarify the application of effective field theory techniques in the context of popular cosmological models, and to explicitly demonstrate how and when higher-derivative operators can be cast into lower-derivative forms suitable for numerical solution techniques.

operator
field theory
general scalar-tensor theory


Angular 21 cm Power Spectrum of a Scaling Distribution of Cosmic String Wakes

Abstract: Cosmic string wakes lead to a large signal in 21 cm redshift maps at redshifts larger than that corresponding to reionization. Here, we compute the angular power spectrum of 21 cm radiation as predicted by a scaling distribution of cosmic strings whose wakes have undergone shock heating.

cosmic string
string wake
angular power spectrum
shock heating


Halo Shape and Relic Density Exclusions of Sommerfeld-Enhanced Dark Matter Explanations of Cosmic Ray Excesses

Abstract: Dark matter with Sommerfeld-enhanced annihilation has been proposed to explain observed cosmic ray positron excesses in the 10 GeV to TeV energy range. We show that the required enhancement implies thermal relic densities that are too small to be all of dark matter. We also show that the dark matter is sufficiently self-interacting that observations of elliptical galactic dark matter halos exclude large Sommerfeld enhancement for light force carriers. Resonant Sommerfeld enhancement does not modify these conclusions, and the astrophysical boosts required to resolve these discrepancies are disfavored, especially when significant self-interactions suppress halo substructure.

dark matter
thermal relic density
dwarf galaxy


The Gamma-Ray Pulsar Population of Globular Clusters: Implications for the GeV Excess

Abstract: It has been suggested that the GeV excess, observed from the region surrounding the Galactic Center, might originate from a population of millisecond pulsars that formed in globular clusters. With this in mind, we employ the publicly available Fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). We combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecond pulsars in the Milky Way's globular cluster system. We find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the Milky Way (i.e. the thick disk). After pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. Using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed GeV excess. Among other challenges, scenarios in which the entire GeV excess is generated from such pulsars are in conflict with the observed mass of the Milky Way's Central Stellar Cluster.

pulsar
globular cluster
luminosity function
central stellar cluster


Hunting for the host galaxy groups of binary black holes and the application in constraining Hubble constant

Abstract: The discovery of gravitational-wave (GW) signals, produced by the coalescence of stellar-mass binary black holes (SBBHs), opens a new window to study the astrophysical origins and dynamical evolutions of compact binaries. In addition, these GW events can be treated as the standard sirens to constrain various cosmological parameters. Both issues require the host identification for these GW events, with help of the spatial resolution of GW detector networks. In this paper, we investigate the capabilities of various detector networks for identifying the SBBHs' host galaxy groups, rather than their host galaxies, which can overcome the influence of galaxies' proper motions in dark matter halos for measuring the cosmological parameters. In our analysis, the group catalog of SDSS DR7 with redshift z∈(0.01,0.1) is considered as an example of the application. We find that for the second-generation (2G) detector network, the host galaxy groups of around (0.7-6.9) SBBHs can be identified per year assuming all sources are 30-30 M_⊙ binaries, and that all five detectors in the network are in lock 100% of the time. For the 3G detector network, this number becomes (3.9-40.0) yr^-1. We also investigate the potential constraint on the Hubble constant H_0 by these GW events, if their redshift information is extracted from the candidates of host galaxy groups. We find that, by five-year's full time observations, 2G detector network is expected to give a constraint of Δ H_0/H_0∼ (1%,4%), which can be more than two order smaller if considering the 3G detector network.

host galaxy group
binary black hole
hubble constant
cosmological parameter


Lensing signals from Spin-2 perturbations

Abstract: We compute the angular power spectra of the E-type and B-type lensing potentials for gravitational waves from inflation and for tensor perturbations induced by scalar perturbations. We derive the tensor-lensed CMB power spectra for both cases. We also apply our formalism to determine the linear lensing potential for a Bianchi I spacetime with small anisotropy.

gravitational wave
tensor perturbation
possible contribution


Constraints on ultra-low-frequency gravitational waves with statistics of pulsar spin-down rates

Abstract: We probe ultra-low-frequency gravitational waves (GWs) with statistics of spin-down rates of milli-second pulsars (MSPs) by a method proposed in our prevous work (Yonemaru et al. 2016). The considered frequency range is 10^-12 Hz≲ f_ GW≲ 10^-10Hz, which cannot be accessed by the conventional pulsar timing array. The effect of such low-frequency GWs appears as a bias to spin-down rates which has a quadrupole pattern in the sky. We use the skewness of the spin-down rate distribution and the number of MSPs with negative spin-down rates to search for the bias induced by GWs. Applying this method to 149 MSPs selected from the ATNF pulsar catalog, we derive upper bounds on the time derivative of the GW amplitudes of ḣ < 6.2 × 10^-18 sec^-1 and ḣ < 8.1 × 10^-18 sec^-1 in the directions of the Galactic Center and M87, respectively. Approximating the GW amplitude as ḣ∼ 2 π f_ GW h, the bounds translate into h < 3 × 10^-9 and h < 4 × 10^-9, respectively, for f_ GW = 1/(100 yr). Finally, we give the implications to possible super-massive black hole binaries at these sites.

ultra-low-frequency gravitational wave
pulsar
spin-down rate


Vector field models of modified gravity and the dark sector

Abstract: We present a comprehensive investigation of cosmological constraints on the class of vector field formulations of modified gravity called Generalized Einstein-Aether models. Using linear perturbation theory we generate cosmic microwave background and large-scale structure spectra for general parameters of the theory, and then constrain them in various ways. We investigate two parameter regimes: a dark-matter candidate where the vector field sources structure formation, and a dark-energy candidate where it causes late-time acceleration. We find that the dark matter candidate does not fit the data, and identify five physical problems that can restrict this and other theories of dark matter. The dark energy candidate does fit the data, and we constrain its fundamental parameters; most notably we find that the theory's kinetic index parameter n_ae can differ significantly from its ΛCDM value.

gravity
cosmology
dark matter
einstein-æther theory


Hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit: I. General formalism and perturbations analysis

Abstract: Using a generalization of the Madelung transformation, we derive the hydrodynamic representation of the Klein-Gordon-Einstein equations in the weak field limit. We consider a complex self-interacting scalar field with a λ|φ|^4 potential. We study the evolution of the homogeneous background in the fluid representation and derive the linearized equations describing the evolution of small perturbations in a static and in an expanding universe. We compare the results with simplified models in which the gravitational potential is introduced by hand in the Klein-Gordon equation, and assumed to satisfy a (generalized) Poisson equation. We study the evolution of the perturbations in the matter era using the nonrelativistic limit of our formalism. Perturbations whose wavelength is below the Jeans length oscillate in time while pertubations whose wavelength is above the Jeans length grow linearly with the scale factor as in the cold dark matter model. The growth of perturbations in the scalar field model is substantially faster than in the cold dark matter model. When the wavelength of the pertubations approaches the cosmological horizon (Hubble length), a relativistic treatment is mandatory. In that case, we find that relativistic effects attenuate or even prevent the growth of pertubations. This paper exposes the general formalism and provides illustrations in simple cases. Other applications of our formalism will be considered in companion papers.

klein-gordon-einstein equation
weak field limit
hydrodynamic representation