Within a sufficiently large cosmic volume, conservation of baryons implies a simple "closed box" view in which the sum of the baryonic components must equal a constant fraction of the total enclosed mass. We present evidence from Rhapsody-G hydrodynamic simulations of massive galaxy clusters that the closed-box expectation may hold to a surprising degree within the interior, non-linear regions of very massive haloes. We find a significant anti-correlation between hot gas mass fraction and galaxy mass fraction (cold gas + stars), with rank correlation coefficient, -0.69, within R500c. Because of this anti-correlation, the total baryon mass serves as a low-scatter proxy for total cluster mass. The fractional scatter in total baryon fraction scales approximately as 0.02 (Delta_c/100)^0.6, while the scatter of either gas mass or stellar mass is larger in magnitude and declines more slowly with increasing radius. We discuss potential observational tests using cluster samples selected by optical and hot gas properties; the simulations suggest that joint selection on stellar and hot gas has potential to achieve 5% scatter in total halo mass.
Counting galaxy number density with wide range sky surveys has been well
adopted in researches focusing on revealing evolution pattern of different
types of galaxies. As understood intuitively the astrophysics environment
physics is intimated affected by cosmology priors with theoretical estimation
or vise versa, or simply stating that the astrophysics effect couples the
corresponding cosmology observations
or the way backwards. In this article we try to quantify the influence on
galaxy number density prediction at faint luminosity limit from the
uncertainties in cosmology, and how much the uncertainties blur the detection
of galaxy evolution, with the hope that this trying may indeed help for precise
and physical cosmology study in near future or vise versa
We present the Swift X-ray Cluster Survey (SWXCS) catalog obtained using archival data from the X-ray telescope (XRT) on board the Swift satellite acquired from 2005 to 2012, extending the first release of the SWXCS. The catalog provides positions, soft fluxes, and, when possible, optical counterparts for a flux-limited sample of X-ray group and cluster candidates. We consider the fields with Galactic latitude |b| > 20 degree to avoid high HI column densities. We discard all of the observations targeted at groups or clusters of galaxies, as well as particular extragalactic fields not suitable to search for faint extended sources. We finally select ~3000 useful fields covering a total solid angle of ~400 degree^2. We identify extended source candidates in the soft-band (0.5-2keV) images of these fields using the software EXSdetect, which is specifically calibrated for the XRT data. Extensive simulations are used to evaluate contamination and completeness as a function of the source signal, allowing us to minimize the number of spurious detections and to robustly assess the selection function. Our catalog includes 263 candidate galaxy clusters and groups down to a flux limit of 7E-15 erg/cm^2/s in the soft band, and the logN-logS is in very good agreement with previous deep X-ray surveys. The final list of sources is cross-correlated with published optical, X-ray, and SZ catalogs of clusters. We find that 137 sources have been previously identified as clusters, while 126 are new detections. Currently, we have collected redshift information for 158 sources (60% of the entire sample). Once the optical follow-up and the X-ray spectral analysis of the sources are complete, the SWXCS will provide a large and well-defined catalog of groups and clusters of galaxies to perform statistical studies of cluster properties and tests of cosmological models.
We consider some models describing interaction between the dark components and obtain an expression for the coupling constant which contains only the cosmographic parameters. It enables us on the one hand to find constrains on the coupling constants using observational data, and on the other hand, given fixed constraints on the coupling, to restrict number of numerous models describing the interaction in the dark sector.
We characterize a cosmic rest frame in which the variation of the spherically averaged Hubble expansion is most uniform, under local Lorentz boosts of the central observer. Using the COMPOSITE sample of 4534 galaxies, we identify a degenerate set of candidate minimum variance frames, which includes the rest frame of the Local Group (LG) of galaxies, but excludes the standard Cosmic Microwave Background (CMB) frame. Candidate rest frames defined by a boost from the LG frame close to the plane of the galaxy have a statistical likelihood similar to the LG frame. This may result from a lack of constraining data in the Zone of Avoidance in the COMPOSITE sample. We extend our analysis to the Cosmicflows-2 (CF2) sample of 8,162 galaxies. While the signature of a systematic boost offset between the CMB and LG frames averages is still detected, the spherically averaged expansion variance in all rest frames is significantly larger in the CF2 sample than would be reasonably expected. We trace this to an omission of any correction for inhomogeneous distribution Malmquist bias in the CF2 distances. Systematic differences in the inclusion of the large SFI++ subsample into the COMPOSITE and CF2 catalogues are analysed. Our results highlight the importance of a careful treatment of Malmquist biases for future peculiar velocities studies, including tests of the hypothesis of Wiltshire et al [arXiv:1201.5371] that a significant fraction of the CMB temperature dipole may be nonkinematic in origin.
We consider gravity theory with varying speed of light and varying gravitational constant. Both constants are represented by non-minimally coupled scalar fields. We examine the cosmological evolution in the near curvature singularity regime. We find that at the curvature singularity the speed of light goes to infinity while the gravitational constant vanishes. This corresponds to the Newton's Mechanics limit represented by one of the vertex of the Bronshtein-Zelmanov-Okun cube. The cosmological evolution includes both the pre-big-bang and post-big-bang phases separated by the curvature singularity. We also investigate the quantum counterpart of the considered theory and find the probability of transition of the universe from the collapsing pre-big-bang phase to the expanding post-big-bang phase.
We formulate a smoothed-particle hydrodynamics numerical method, traditionally used for the Euler equations for fluid dynamics in the context of astrophysical simulations, to solve the non-linear Schrodinger equation in the Madelung formulation. The probability density of the wavefunction is discretized into moving particles, whose properties are smoothed by a kernel function. The traditional fluid pressure is replaced by a quantum pressure tensor, for which a novel, robust discretization is found. We demonstrate our numerical method on a variety of numerical test problems involving the simple harmonic oscillator, Bose-Einstein condensates, collapsing singularities, and dark matter halos governed by the Gross-Pitaevskii-Poisson equation. Our method is conservative, applicable to unbounded domains, and is automatically adaptive in its resolution, making it well suited to study problems with collapsing solutions.
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. Nonspherical long-wavelength solutions are particularly important for primordial structure formation in the epoch of soft equations of state. Applying this framework to spherical symmetry, we show the equivalence between long-wavelength solutions in the constant mean curvature slicing and asymptotic quasi-homogeneous solutions in the comoving slicing. We derive the correspondence relation and compare the results of numerical simulations of primordial black hole (PBH) formation. In terms of $\tilde{\delta}_{c}$, the value which the averaged density perturbation at threshold in the comoving slicing would take at horizon entry in the first-order long-wavelength expansion, we find that the sharper the transition from the overdense region to the FRW universe is, the larger the $\tilde{\delta}_{c}$ becomes. We suggest that, for $p=(\Gamma-1)\rho$, we can apply the analytic formula for the minimum $\tilde{\delta}_{c, {\rm min}} \simeq 3\Gamma/(3\Gamma+2)\sin^2 \left[\pi\sqrt{\Gamma-1}/(3\Gamma-2)\right]$ and the maximum $\tilde{\delta}_{c, {\rm max}} \simeq 3\Gamma/(3\Gamma+2)$. As for the threshold peak value of the curvature perturbation $\psi_{0,c}$, we find that the sharper the transition is, the smaller the $\psi_{0,c}$ becomes. We explain this intriguing feature with a compensated top-hat density model. We also deduce an environmental effect in the presence of much longer wavelength perturbations using simplified models. We conclude that PBH formation can be significantly suppressed (enhanced) in the underlying positive (negative) density perturbation of longer wavelength, provided that the smaller value of $\psi_{0,c}$ implies higher production rate of PBHs.
We present a first application of the subhalo abundance matching (SHAM) method to describe the redshift-space clustering of galaxies including the non-linear redshift-space distortion, i.e., the Fingers-of-God. We find that the standard SHAM connecting the luminosity of galaxies to the maximum circular velocity of subhalos well reproduces the luminosity dependence of redshift-space clustering of galaxies in the Sloan Digital Sky Survey in a wide range of scales from 0.3 to 40 Mpc/h. The result indicates that the SHAM approach is very promising for establishing a theoretical model of redshift-space galaxy clustering without additional parameters. We also test color abundance matching using two different proxies for colors: subhalo age and local dark matter density following the method by Masaki et al. (2013b). Observed clustering of red galaxies exhibits much stronger Fingers-of-God effect than blue galaxies. We find that the subhalo age model describes the observed color-dependent redshift-space clustering much better than the local dark matter density model. The result infers that the age of subhalos is a key ingredient to determine the color of galaxies.
We constrain the effective theory of one-body dark matter-nucleon interactions using neutrino telescope observations. We derive exclusion limits on the 28 coupling constants of the theory, exploring interaction operators previously considered in dark matter direct detection only, and using new nuclear response functions recently derived through nuclear structure calculations. We determine for what interactions neutrino telescopes are superior to current direct detection experiments, and show that Hydrogen is not the most important element in the exclusion limit calculation for the majority of the spin-dependent operators.
By insisting on naturalness in both the electroweak and QCD sectors of the MSSM, the portrait for dark matter production is seriously modified from the usual WIMP miracle picture. In SUSY models with radiatively-driven naturalness (radiative natural SUSY or RNS) which include a DFSZ-like solution to the strong CP and SUSY mu problems, dark matter is expected to be an admixture of both axions and higgsino-like WIMPs. The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter space, axions make up the dominant contribution of dark matter although regions of WIMP dominance also occur. We show the allowed range of PQ scale f_a and compare to the values expected to be probed by the ADMX axion detector in the near future. We also show WIMP detection rates which are suppressed from usual expectations because now WIMPs comprise only a fraction of the total dark matter. Nonetheless, ton-scale noble liquid detectors should be able to probe the entirety of RNS parameter space. Indirect WIMP detection rates are less propitious since they are reduced by the square of the depleted WIMP abundance.
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We examine the stellar mass assembly in galaxy cluster cores using data from the Cluster Lensing and Supernova survey with Hubble (CLASH). We measure the growth of brightest cluster galaxy (BCG) stellar mass, the fraction of the total cluster light which is in the intracluster light (ICL) and the numbers of mergers that occur in the BCG over the redshift range of the sample, 0.18<z<0.90. We find that BCGs grow in stellar mass by a factor of 1.4 on average from accretion of their companions, and this growth is reduced to a factor of 1.2 assuming 50% of the accreted stellar mass becomes ICL, in line with the predictions of simulations. We find that the ICL shows significant growth over this same redshift range, growing by a factor of of 4--5 in its contribution to the total cluster light. This result is in line with our previous findings for ICL at higher redshifts, however our measured growth is somewhat steeper than is predicted by simulations of ICL assembly. We find high mass companions and hence major merging (mergers with objects of masses $\geq$1/2 of the BCG) to be very rare for our sample. We conclude that minor mergers (mergers with objects with masses $<$ 1/2 of the BCG) are the dominant process for stellar mass assembly at low redshifts, with the majority of the stellar mass from interactions ending up contributing to the ICL rather than building up the BCG. From a rough estimate of the stellar mass growth of the ICL we also conclude that the majority of the ICL stars must come from galaxies which fall from outside of the core of the cluster, as is predicted by simulations. It appears that the growth of the ICL is the major evolution event in galaxy cluster cores during the second half of the lifetime of the Universe.
In this work we study the relevance of the cosmic web and substructures on the matter and lensing power spectra measured from halo mock catalogues extracted from the N-body simulations. Since N-body simulations are computationally expensive, it is common to use faster methods that approximate the dark matter field as a set of halos. In this approximation, we replace mass concentrations in N-body simulations by a spherically symmetric Navarro-Frenk-White halo density profile. We also consider the full mass field as the sum of two distinct fields: dark matter halos ($M>9\times 10^{12}~M_{\odot}$/h) and particles not included into halos. Mock halos reproduce well the matter power spectrum, but underestimate the lensing power spectrum on large and small scales. For sources at $z_{\rm s}=1$ the lensing power spectrum is underestimated by up to 40% at $\ell\approx 10^4$ with respect to the simulated halos. The large scale effect can be alleviated by combining the mock catalogue with the dark matter distribution outside the halos. In addition, to evaluate the contribution of substructures we have smeared out the intra-halo substructures in a N-body simulation while keeping the halo density profiles unchanged. For the matter power spectrum the effect of this smoothing is only of the order of 5%, but for lensing substructures are much more important: for $\ell\approx 10^4$ the internal structures contribute 30% of the total spectrum. These findings have important implications in the way mock catalogues have to be created, suggesting that some approximate methods currently used for galaxy surveys will be inadequate for future weak lensing surveys.
We perform a weak-lensing study of the nearby cool-core galaxy clusters, Hydra A ($z=0.0538$) and A478 ($z=0.0881$), of which brightest cluster galaxies (BCGs) host powerful activities of active galactic nuclei (AGNs). For each cluster, the observed tangential shear profile is well described either by a single Navarro--Frenk--White model or a two-component model including the BCG as an unresolved point mass. For A478, we determine the BCG and its host-halo masses from a joint fit to weak-lensing and stellar photometry measurements. We find that the choice of initial mass functions (IMFs) can introduce a factor of two uncertainty in the BCG mass, whereas the BCG host halo mass is well constrained by data. We perform a joint analysis of weak-lensing and stellar kinematics data available for the Hydra A cluster, which allows us to constrain the central mass profile without assuming specific IMFs.We find that the central mass profile ($r<300$ kpc) determined from the joint analysis is in excellent agreement with those from independent measurements,including dynamical masses estimated from the cold gas disk component, X-ray hydrostatic total mass estimates,and the central stellar mass estimated based on the Salpeter IMF. The observed dark-matter fractions around the BCGs for the two clusters are found to be smaller than those predicted by adiabatic contraction models, suggesting the importance of other physical processes, such as the the AGN feedback and/or dissipationless mergers.
We obtain a consistency relation for the observed three-point correlator of galaxies. It includes relativistic effects and it is valid in the squeezed limit. Furthermore, the consistency relation is non-perturbative and can be used at arbitrarily small scales for the short modes. Our results are also useful to compute the non-linear relativistic corrections which induce a signal in the observations that might be misinterpreted as primordial non-Gaussianity with a local shape. We estimate the effective local non-Gaussianity parameter from the relativistic corrections. The exact value depends on the redshift and the magnification bias. At redshift of $ z = 1$, in the absence of magnification bias, we get $\,\, f^{\rm GR}_{\rm NL} \simeq - 3.7 $.
Imposing that the excursion distance of inflaton in field space during inflation be less than the Planck scale, we derive an upper bound on the tensor-to-scalar ratio at the CMB scales, i.e. $r_{*,max}$, in the general canonical single-field slow-roll inflation model, in particular the model with non-negligible running of the spectral index $\alpha_s$ and/or the running of running $\beta_s$. We find that $r_{*,max}\simeq 7\times 10^{-4}$ for $n_s=0.9645$ without running and running of running, and $r_{*,max}$ is significantly relaxed to the order of ${\cal O}(10^{-2}\sim 10^{-1})$ in the inflation model with $\alpha_s$ and/or $\beta_s\sim +{\cal O}(10^{-2})$ which are marginally preferred by the Planck 2015 data.
We propose a new method of calculating a dark matter halo mass function based on the rescaling of a mass function measured in simulations. Our tests show that the accuracy almost linearly depends on the difference of the cosmological parameters and amounts to few percent in the case of WMAP5 and PLANCK parameters.
Initially cold and spherically symmetric self-gravitating systems may give rise to a virial equilibrium state which is far from spherically symmetric, and typically triaxial. We focus here on how the degree of symmetry breaking in the final state depends on the initial density profile. We note that the most asymmetric structures result when, during the collapse phase, there is a strong injection of energy preferentially into the particles which are localized initially in the outer shells. These particles are still collapsing when the others, initially located in the inner part, are already re-expanding; the motion of particles in a time varying potential allow them to gain kinetic energy --- in some cases enough to be ejected from the system. We show that this mechanism of energy gain amplifies the initial small deviations from perfect spherical symmetry due to finite $N$ fluctuations. This amplification is more efficient when the initial density profile depends on radius, because particles have a greater spread of fall times compared to a uniform density profile, for which very close to symmetric final states are obtained}. These effects lead to a distinctive correlation of the orientation of the final structure with the distribution of ejected mass, and also with the initial (very small) angular fluctuations.
Radio-loud Active Galactic Nuclei at z~2-4 are typically located in dense environments and their host galaxies are among the most massive systems at those redshifts, providing key insights for galaxy evolution. Finding radio-loud quasars at the highest accessible redshifts (z~6) is important to study their properties and environments at even earlier cosmic time. They would also serve as background sources for radio surveys intended to study the intergalactic medium beyond the epoch of reionization in HI 21 cm absorption. Currently, only five radio-loud ($R=f_{\nu,5{\rm GHz}}/f_{\nu,4400\AA}>10$) quasars are known at z~6. In this paper we search for 5.5 < z < 7.2 quasars by cross-matching the optical Pan-STARRS1 and radio FIRST surveys. The radio information allows identification of quasars missed by typical color-based selections. While we find no good 6.4 < z <7.2 quasar candidates at the sensitivities of these surveys, we discover two new radio-loud quasars at z~6. Furthermore, we identify two additional z~6 radio-loud quasars which were not previously known to be radio-loud, nearly doubling the current z~6 sample. We show the importance of having infrared photometry for z>5.5 quasars to robustly classify them as radio-quiet or radio-loud. Based on this, we reclassify the quasar J0203+0012 (z=5.72), previously considered radio-loud, to be radio-quiet. Using the available data in the literature, we constrain the radio-loud fraction of quasars at z~6, using the Kaplan--Meier estimator, to be $8.1^{+5.0}_{-3.2}\%$. This result is consistent with there being no evolution of the radio-loud fraction with redshift, in contrast to what has been suggested by some studies at lower redshifts.
Gamma-ray bursts (GRBs) offer a route to characterizing star-forming galaxies and quantifying high-$z$ star-formation that is distinct from the approach of traditional galaxy surveys: GRB selection is independent of dust and probes even the faintest galaxies that can evade detection in flux-limited surveys. However, the exact relation between GRB rate and Star Formation Rate (SFR) throughout all redshifts is controversial. The TOUGH survey includes observations of all GRB hosts (69) in an optically unbiased sample and we utilize these to constrain the evolution of the UV GRB-host-galaxy Luminosity Function (LF) between $z=0$ and $z=4.5$, and compare this with LFs derived from both Lyman-break galaxy (LBG) surveys and simulation modeling. At all redshifts we find the GRB hosts to be most consistent with a Luminosity Function derived from SFR weighted models incorporating GRB production via both metallicity-dependent and independent channels with a relatively high level of bias towards low metallicity hosts. In the range $1<z<3$ an SFR weighted LBG derived (i.e. non-metallicity biased) LF is also a reasonable fit to the data. Between $z\sim3$ and $z\sim6$, we observe an apparent lack of UV bright hosts in comparison with Lyman-break galaxies, though the significance of this shortfall is limited by nine hosts of unknown redshift.
We present a detailed exploration of a family of low--$\ell$ angular power spectra inspired by "Brane Supersymmetry Breaking". This mechanism splits Bose and Fermi excitations in String Theory and leaves behind \emph{an exponential potential that is just too steep for the inflaton to emerge from the initial singularity while descending it}. As a result, the scalar generically bounces against the exponential wall, which typically introduces \emph{an infrared depression and a pre--inflationary peak} in the power spectrum of scalar perturbations. We elaborate on a possible link between this phenomenon and the low--$\ell$ CMB. For the first 32 multipoles, combining the hard exponential with a milder one leading to $n_s\simeq 0.96$ and with a small gaussian bump we have attained a reduction of $\chi^{\,2}$ to about 46\% of the standard $\Lambda$CDM setting, with both WMAP9 and PLANCK 2013 data. This result corresponds to a $\chi^{\,2}/DOF$ of about 0.45, to be compared with a $\Lambda$CDM value of about 0.85. The preferred choices combine naturally quadrupole depression, a first peak around $\ell=5$ and a wide minimum around $\ell=20$. We have also gathered some evidence that similar spectra emerge if the hard exponential is combined with more realistic models of inflation.
We undertake a non-perturbative study of the evolution of the "gravitational entropy" proposed by Clifton, Ellis and Tavakol (CET) on local expanding cosmic CDM voids of $\sim 50-100$ Mpc size described as spherical under-dense regions with negative spatial curvature, whose dynamics is determined by Lemaitre-Tolman-Bondi (LTB) dust models asymptotic to three different types of FLRW background: $\Lambda$CDM, Einstein de Sitter and "open" FLRW with $\Lambda=0$ and negative spatial curvature. By assuming generic nearly spatially flat and linear initial conditions at the last scattering time, we examine analytically and numerically the CET entropy evolution into a fully non-linear regime in our present cosmic time and beyond. Both analytic and numerical analysis reveal that the late time CET entropy growth is determined by the amplitude of initial fluctuations of spatial curvature at the last scattering time. This entropy growth decays to zero in the late asymptotic time range for all voids, but at a faster rate in voids with $\Lambda$CDM and open FLRW backgrounds. However, only for voids in a $\Lambda$CDM background this suppression is sufficiently rapid for the CET entropy itself to reach a terminal equilibrium (or "saturation") value. The CET gravitational temperature vanishes asymptotically if $\Lambda=0$ and becomes asymptotically proportional to $\Lambda$ for voids in a $\Lambda$CDM background. In the linear regime of the LTB evolution our results coincide, qualitatively and quantitatively, with previous results based on linear perturbation theory.
Cosmological inflation is discussed in the framework of $F(R,{\cal G})$ gravity where $F$ is a generic function of the curvature scalar $R$ and the Gauss-Bonnet topological invariant $\cal G$. The main feature that emerges in this analysis is the fact that this kind of theory can exhaust all the curvature budget related to curvature invariants without considering derivatives of $R,$ $R_{\mu\nu}$, $R^{\lambda}_{\sigma\mu\nu}$ etc. in the action. Cosmological dynamics results driven by two effective masses (lenghts) related to the $R$ scalaron and the $\cal G$ scalaron working respectively at early and very early epochs of cosmic evolution. In this sense, a double inflationary scenario naturally emerges.
Mapping the polarization of the Cosmic Microwave Background is yielding exciting data on the origin of the universe, the reionization of the universe, and the growth of cosmic structure. Kilopixel arrays represent the current state of the art, but advances in detector technology are needed to enable the larger detector arrays needed for future measurements. Here we present a design for single-band dual-polarization Kinetic Inductance Detectors (KIDs) at 20% bandwidths centered at 145, 220, and 280 GHz. The detection and readout system is nearly identical to the successful photon-noise-limited aluminum Lumped-Element KIDs that have been recently built and tested by some of the authors. Fabricating large focal plane arrays of the feed horns and quarter-wave backshorts requires only conventional precision machining. Since the detectors and readout lines consist only of a single patterned aluminum layer on a SOI wafer, arrays of the detectors can be built commercially or at a standard university cleanroom.
Based on the quantum effective action we compute for interacting theories the time evolution of correlation functions in inflationary cosmology. We neglect non-linearities due to backreaction, an explicit space-time dependence of the effective action reflecting boundary effects, and higher than second time derivatives. In this approximation the information about the state of the universe at the beginning of inflation remains imprinted on the observable primordial fluctuation spectrum. We therefore observe the initial spectrum, processed only mildly by the scale-violating effects at horizon crossing induced by the inflaton potential. Depending on initial conditions the relation between amplitude and Hubble parameter at the time of horizon crossing or the spectral index can be modified. Observations of the cosmic microwave background can gain information on the inflaton potential only if either the omitted non-linear effects lead to a fast enough symmetrization and dissipation of the initial spectrum, or if the initial spectrum can be constrained. The latter may be realized if inflation lasts sufficiently long before the time of horizon crossing and the ultraviolet behavior of correlation functions is the same as for flat space.
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In models like axion monodromy, temporal features during inflation which are not associated with its ending can produce scalar, and to a lesser extent, tensor power spectra where deviations from scale-free power law spectra can be as large as the deviations from scale invariance itself. Here the standard slow-roll approach breaks down since its parameters evolve on an efolding scale $\Delta N$ much smaller than the efolds to the end of inflation. Using the generalized slow-roll approach, we show that the expansion of observables in a hierarchy of potential or Hubble evolution parameters comes from a Taylor expansion of the features around an evaluation point that can be optimized. Optimization of the leading order expression provides a sufficiently accurate approximation for current data as long as the power spectrum can be described over the well-observed few efolds by the local tilt and running. Standard second order approaches, often used in the literature, ironically are worse than leading order approaches due to inconsistent evaluation of observables. We develop a new optimized next order approach which predicts observables to $10^{-3}$ even for $\Delta N\sim 1$ where all parameters in the infinite hierarchy are of comparable magnitude. For models with $\Delta N \ll 1$, the generalized slow-roll approach provides integral expressions that are accurate to second order in the deviation from scale invariance. Their evaluation in the monodromy model provides highly accurate explicit relations between the running oscillation amplitude, frequency and phase in the curvature spectrum and parameters of the potential.
Primordial magnetic fields (PMF) damp at scales smaller than the photon diffusion and free-streaming scale. This leads to heating of ordinary matter (electrons and baryons), which affects both the thermal and ionization history of our Universe. Here, we study the effect of heating due to ambipolar diffusion and decaying magnetic turbulence. We find that changes to the ionization history computed with recfast are significantly overestimated when compared with CosmoRec. The main physical reason for the difference is that the photoionization coefficient has to be evaluated using the radiation temperature rather than the matter temperature. A good agreement with CosmoRec is found after changing this aspect. Using Planck 2013 data and considering only the effect of PMF-induced heating, we find an upper limit on the r.m.s. magnetic field amplitude of B0 < 1.1 nG (95% c.l.) for a stochastic background of PMF with a nearly scale-invariant power spectrum. We also discuss uncertainties related to the approximations for the heating rates and differences with respect to previous studies. Our results are important for the derivation of constraints on the PMF power spectrum obtained from measurements of the cosmic microwave background anisotropies with full-mission Planck data. They may also change some of the calculations of PMF-induced effects on the primordial chemistry and 21cm signals.
In arXiv:1502.01250, we have recently argued that when the energy of a photon injected in the primordial plasma falls below the pair-production threshold, the universality of the non-thermal photon spectrum from the standard theory of electromagnetic cascades onto a photon background breaks down. We showed that this could reopen or widen the parameter space for an exotic solution to the 'lithium problem'. Here we discuss another application, namely the impact that this has on non-thermal big bang nucleosynthesis constraints from 4He, 3He and 2H, using the parametric example of monochromatic photon injection of different energies. Typically, we find tighter bounds than those existing in the literature, up to more than one order of magnitude. As a consequence of the non-universality of the spectrum, the energy-dependence of the photodissociation cross-sections is important. We also compare the constraints obtained with current level and future reach of cosmic microwave background spectral distortion bounds.
We test a model of inflation with a fast-rolling kinetic dominated initial condition against data from Planck using MCMC. We choose a m^2 {\phi}^2 potential and perform a full numerical calculation of both the scalar and tensor primordial power spectra. We find a slight improvement in fit for this model over the standard eternal slow roll case.
Beyond the linear regime of structure formation, part of cosmological information encoded in galaxy clustering becomes inaccessible to the usual power spectrum. "Sufficient statistics", A*, were introduced recently to recapture the lost, and ultimately extract all, cosmological information. We present analytical approximations for the A* and traditional power spectra as well as for their covariance matrices in order to calculate analytically their cosmological information content in the context of Fisher information theory. Our approach allows the precise quantitative comparison of the techniques with each other and to the total information in the data, and provides insights into sufficient statistics. In particular, we find that while the A* power spectrum has a similar shape to the usual galaxy power spectrum, its amplitude is strongly modulated by small scale statistics. This effect is mostly responsible for the ability of the A* power spectrum to recapture the information lost for the usual power spectrum. We use our framework to forecast the best achievable cosmological constraints for projected surveys as a function of their galaxy density, and compare the information content of the two power spectra. We find that sufficient statistics extract all cosmological information, resulting in an approximately factor of ~2 gain for dense projected surveys at low redshift. This increase in the effective volume of projected surveys is consistent with previous numerical calculations.
Recently, Sahni, Shafielo o & Starobinsky (2014) combined two independent measurements of $H(z)$ from BAO data with the value of the Hubble constant $H_0 = H(z=0)$, in order to test the cosmological constant hypothesis by means of an improved version of the $Om$ diagnostic. Their result indicated a considerable tension between observations and predictions of the $\Lambda$CDM model. However, such strong conclusion was based only on three measurements of $H(z)$. This motivated us to repeat similar work on a larger sample. By using a comprehensive data set of 29 $H(z)$, we find that discrepancy indeed exists. Even though the value of $\Omega_{m,0} h^2$ inferred from $Omh^2$ diagnostic depends on the way one chooses to make a summary statistics (weighted mean or the median), the persisting discrepancy supports the claims of Sahni, Shafielo o & Starobinsky (2014) that $\Lambda$CDM model may not be the best description of our Universe.
Cosmological tests based on the statistical analysis of galaxy distributions are usually dependent on the evolution of the sources. An exception is the Alcock-Paczynski (AP) test, which is based on the changing ratio of angular to spatial/redshift size of (presumed) spherically-symmetric source distributions with distance. Intrinsic redshift distortions due to gravitational effects may also have an influence, but there is now a way to overcome them: with the inclusion in the AP test of an observational signature with a sharp feature, such as the Baryonic Acoustic Oscillation (BAO) peak. Redshift distortions affect only the amplitude of the peak, not its position. As we will show here, the use of this diagnostic, with newly acquired data on the anisotropic distribution of the BAO peaks from SDSS-III/BOSS-DR11 at average redshifts 0.57 and 2.34, strongly disfavours the current concordance (LCDM) model, which is discarded at the 3-sigma level. A statistically acceptable fit to the AP data with wCDM (the version of LCDM with a dark-energy equation of state w_de=p_de/rho_de rather than w_de=w_L=-1) is possible only with w_de=-0.24{+0.60}{-0.42} and Omega_m=0.74{+0.22}{-0.33}. Within the context of expanding Friedmann-Robertson-Walker (FRW) cosmologies, these data strongly favour the zero `active mass' equation-of-state, the basis for the R_h=ct Universe, in which rho+3p=0, where rho and p are, respectively, the total density and pressure of the cosmic fluid.
We study the detailed evolution of the fine-structure constant $\alpha$ in the string-inspired runaway dilaton class of models of Damour, Piazza and Veneziano. We provide constraints on this scenario using the most recent $\alpha$ measurements and discuss ways to distinguish it from alternative models for varying $\alpha$. For model parameters which saturate bounds from current observations, the redshift drift signal can differ considerably from that of the canonical $\Lambda$CDM paradigm at high redshifts. Measurements of this signal by the forthcoming European Extremely Large Telescope (E-ELT), together with more sensitive $\alpha$ measurements, will thus dramatically constrain these scenarios.
We discuss quantum gravitational effects in Einstein theory coupled to periodic axion scalars to analyze the viability of several proposals to achieve superplanckian axion periods (aka decay constants) and their possible application to large field inflation models. The effects we study correspond to the nucleation of euclidean gravitational instantons charged under the axion, and our results are essentially compatible with (but independent of) the Weak Gravity Conjecture, as follows: Single axion theories with superplanckian periods contain gravitational instantons inducing sizable higher harmonics in the axion potential, which spoil superplanckian inflaton field range. A similar result holds for multi-axion models with lattice alignment (like the Kim-Nilles-Peloso model). Finally, theories with $N$ axions can still achieve a moderately superplanckian periodicity (by a $\sqrt{N}$ factor) with no higher harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in this case due to the absence of some instantons, which are forbidden by a discrete $\mathbf{Z}_N$ gauge symmetry. Finally we discuss the realization of these instantons as euclidean D-branes in string compactifications.
We investigate the abundance of galactic molecular hydrogen (H$_2$) in the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) cosmological hydrodynamic simulations. We assign H$_2$ masses to gas particles in the simulations in post-processing using two different prescriptions that depend on the local dust-to-gas ratio and the interstellar radiation field. Both result in H$_2$ galaxy mass functions that agree well with observations in the local and high-redshift Universe. The simulations reproduce the observed scaling relations between the mass of H$_2$ and the stellar mass, star formation rate and stellar surface density. Towards high edshifts, galaxies in the simulations display larger H$_2$ mass fractions, and correspondingly lower H$_2$ depletion timescales, also in good agreement with observations. The comoving mass density of H$_2$ in units of the critical density, $\Omega_{\rm H_2}$, peaks at $z\approx 1.2-1.5$, later than the predicted peak of the cosmic star formation rate activity, at $z\approx 2$. This difference stems from the decrease in gas metallicity and increase in interstellar radiation field with redshift, both of which hamper H$_2$ formation. We find that the cosmic H$_2$ budget is dominated by galaxies with $M_{\rm H_2}>10^9\,\rm M_{\odot}$, star formation rates $>10\,\rm M_{\odot}\,\rm yr^{-1}$ and stellar masses $M_{\rm stellar}>10^{10}\,\rm M_{\odot}$, which are readily observable in the optical and near-IR. The match between the H$_2$ properties of galaxies that emerge in the simulations and observations is remarkable, particularly since it involves no adjustable parameters.
We present a common chiral power-counting scheme for vector, axial-vector, scalar, and pseudoscalar WIMP-nucleon interactions, and derive all one- and two-body currents up to third order in the chiral expansion. Matching our amplitudes to non-relativistic effective field theory, we find that chiral symmetry predicts a hierarchy amongst the non-relativistic operators. Moreover, we identify interaction channels where two-body currents that so far have not been accounted for become relevant.
We introduce project NIHAO (Numerical Investigation of a Hundred Astrophysical Objects), a set of 100 cosmological zoom-in hydrodynamical simulations performed using the GASOLINE code, with an improved implementation of the SPH algorithm. The haloes in our study range from dwarf to Milky Way masses, and represent an unbiased sampling of merger histories, concentrations and spin parameters. The particle masses and force softenings are chosen to resolve the mass profile to below 1% of the virial radius at all masses, ensuring that galaxy half-light radii are well resolved. Using the same treatment of star formation and stellar feedback for every object, the simulated galaxies reproduce the observed inefficiency of galaxy formation across cosmic time as expressed through the stellar mass vs halo mass relation, and the star formation rate vs stellar mass relation. We thus conclude that stellar feedback is the chief piece of physics required to limit the efficiency of star formation in galaxies less massive than the MilkyWay.
We formulate a theory combining the principles of a scalar-tensor gravity and the Rastall proposal of a violation of the usual conservation laws. In the resulting Brans-Dicke-Rastall (BDR) theory the only exact, static, spherically symmetric solution is a Robinson-Bertotti type solution besides the trivial Schwarzschild one. The PPN constraints can be completely satisfied for some values of the free parameters.The cosmological solutions display, among others, a decelerate-accelerate transition in the matter dominated phase.
An isolated, initially cold and ellipsoidal cloud of self-gravitating particles represents a relatively simple system to study the effects of the deviations from spherical symmetry in the mechanism of violent relaxation. Initial deviations from spherical symmetry are shown to play a dynamical role that is equivalent to that of density fluctuations in the case of an initially spherical cloud. Indeed, these deviations control the amount of particles energy change and thus determine the properties of the final energy distribution, particularly the appearance of two species of particles: bound and free. Ejection of mass and energy from the system together with the formation of a density profile decaying as $\rho(r) \sim r^{-4}$ and a Keplerian radial velocity dispersion profile, are the prominent features similar to those observed after the violent relaxation of spherical clouds. In addition, we find that ejected particles are characterized by highly non-spherical shapes, whose features can be traced in the initial deviations from spherical symmetry that are amplified during the dynamical evolution: particles can indeed form anisotropic configurations, like bars and/or disks, even though the initial cloud was very close to spherical.
Among the different methods to derive particle creation, finding the quantum stress tensor expectation value gives a covariant quantity which can be used for examining the back-reaction issue. However this tensor also includes vacuum polarization in a way that depends on the vacuum chosen. Here we review different aspects of particle creation by looking at energy conservation and at the quantum stress tensor. It will be shown that in the case of general spherically symmetric black holes that have a \emph{dynamical horizon}, as occurs in a cosmological context, one cannot have pair creation on the horizon because this violates energy conservation. This confirms the results obtained in other ways in a previous paper [25]. Looking at the expectation value of the quantum stress tensor with three different definitions of the vacuum state, we study the nature of particle creation and vacuum polarization in black hole and cosmological models, and the associated stress energy tensors. We show that the thermal temperature that is calculated from the particle flux given by the quantum stress tensor is compatible with the temperature determined by the affine null parameter approach. Finally, it will be shown that in the spherically symmetric dynamic case, we can neglect the backscattering term and only consider the s-waves term near the future apparent horizon.
Many astrophysical sources radiate via synchrotron emission from relativistic electrons. The electrons give off their kinetic energy as radiation and this radiative loss modifies the electron energy distribution. An analytical treatment of this problem is possible in asymptotic limits by employing the continuity equation. In this article, we are using a probabilistic approach to obtain the analytical results. The basic logic behind this approach is that any particle distribution can be viewed as a probability distribution after normalizing it (as is done frequently in statistical mechanics withi ensembles containing very large number of particles). We are able to reproduce the established results from our novel approach. Same approach can be applied to other physics problems involving spatial or temporal evolution of distribution functions.
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Luminous Red Galaxies (LRG) from the Sloan Digital Sky Survey are considered among the best understood samples of galaxies, and they are employed in a broad range of cosmological studies. Because they form a relatively homogeneous population, with high stellar masses and red colors, they are expected to occupy halos in a relatively simple way. In this paper, we study how LRGs occupy massive halos via direct counts in clusters and we reveal several unexpected trends suggesting that the connection between LRGs and dark matter halos may not be straightforward. Using the redMaPPer cluster catalog, we derive the central occupation of LRGs as a function richness, Ncen({\lambda}). Assuming no correlation between cluster mass and central galaxy luminosity at fixed richness, we show that clusters contain a significantly lower fraction of central LRGs than predicted from the two-point correlation function. At halo masses of 10^14.5 Msun, we find Ncen=0.73, compared to Ncen of 0.89 from correlation studies. Our central occupation function for LRGs converges to 0.95 at large halo masses. A strong anti-correlation between central luminosity and cluster mass at fixed richness is required to reconcile our results with those based on clustering studies. We also derive P_BNC, the probability that the brightest cluster member is not the central galaxy. We find P_BNC ~ 20-30% which is a factor of ~2 lower than the value found by Skibba et al. 2011. Finally, we study the radial offsets of bright non-central LRGs from cluster centers and show that bright non-central LRGs follow a different radial distribution compared to red cluster members, which follow a Navarro-Frank-White profile. This work demonstrates that even the most massive clusters do not always have an LRG at the center, and that the brightest galaxy in a cluster is not always the central galaxy.
We calculate Lyman Alpha Emitter (LAE) angular correlation functions (ACFs) at $z\simeq6.6$ and the fraction of lifetime (for the 100 Myrs preceding $z\simeq6.6$) galaxies spend as Lyman Break Galaxies (LBGs) with/without Lyman Alpha (Ly\alpha) emission using a model that combines SPH cosmological simulations (GADGET-2), dust attenuation and a radiative transfer code (pCRASH). The ACFs are a powerful tool that significantly narrows the 3D parameter space allowed by LAE Ly$\alpha$ and UV luminosity functions (LFs) alone. With this work, we simultaneously constrain the escape fraction of ionizing photons $f_{esc}=0.05-0.5$, the mean fraction of neutral hydrogen in the intergalactic medium (IGM) $<\chi_{HI}>\leq 0.01$ and the dust-dependent ratio of the escape fractions of Ly$\alpha$ and UV continuum photons $f_\alpha/f_c=0.6-1.2$. Our results show that reionization has the largest impact on the amplitude of the ACFs, and its imprints are clearly distinguishable from those of $f_{esc}$ and $f_\alpha/f_c$. We also show that galaxies with a critical stellar mass of $M_* = 10^{8.5} (10^{9.5}) M_\odot$ produce enough luminosity to stay visible as LBGs (LAEs). Finally, the fraction of time during the past 100 Myrs prior to z=6.6 a galaxy spends as a LBG with (without) Lya emission increases with the UV magnitude (and $M_*$): considering observed (dust and IGM attenuated) luminosities, the fraction of time a galaxy spends as a LBG (LAE) increases from 65% to 100% (0-100%) as $M_{UV}$ decreases from $M_{UV} = -18.0$ to $-23.5$ ($M_*$ increases from $10^8-10^{10.5} M_\odot$). Thus in our model the brightest (most massive) LBGs most often show Ly$\alpha$ emission.
We address the problem of line confusion in intensity mapping surveys and explore the possibility to mitigate line foreground contamination by progressively masking the brightest pixels in the observed map. We consider experiments targeting CO(1-0) at $z=3$, Ly$\alpha$ at $z=7$, and CII at $z=7$, and use simulated intensity maps, which include both clustering and shot noise components of the signal and possible foregrounds, in order to test the efficiency of our method. We find that for CO and Ly$\alpha$ it is quite possible to remove most of the foreground contribution from the maps via only 1%-3% pixel masking. The CII maps will be more difficult to clean, however, due to instrumental constraints and the high-intensity foreground contamination involved. While the masking procedure sacrifices much of the astrophysical information present in our maps, we demonstrate that useful cosmological information in the targeted lines can be successfully retrieved.
At the beginning of inflation, when the vacuum energy starts to dominate, there could be many dynamical fields in the Universe. At the same time, velocity of the inflaton may not coincide with the slow-roll (attractor) velocity. Although these additional degrees of freedom may neither enhance nor suppress the curvature perturbation, they can easily alter the scale-dependence of the spectrum. Therefore, if the perturbations exit horizon during the early stage of inflation where these effects are still not negligible, one might observe peculiar scale dependence in the spectrum. We show that the effect can be measured using the running of the tensor mode.
In this work we consider non-zero circular polarization for the CMB radiation as a result of new interactions. We then rewrite the Boltzmann equations for the Stokes parameters $Q$, $U$ and $V$ and show that the circular polarization can generate the B-mode polarization even if no tensor perturbations are present.
Full sky surveys of peculiar velocity are arguably the best way to map the large scale structure out to distances of a few times 100 Mpc/h. Using the largest and most accurate ever catalog of galaxy peculiar velocities "Cosmicflows-2", the large scale structure has been reconstructed by means of the Wiener filter and constrained realizations assuming as a Bayesian prior model the LCDM model with the WMAP inferred cosmological parameters. The present paper focuses on studying the bulk flow of the local flow field, defined as the mean velocity of top-hat spheres with radii ranging out to R=500 Mpc/h. The estimated large scale structures, in general, and the bulk flow, in particular, are determined by the tension between the observational data and the assumed prior model. A prerequisite for such an analysis is the requirement that the estimated bulk flow is consistent with the prior model. Such a consistency is found here. At R=50(150) Mpc/h the estimated bulk velocity is 250+/-21 (239+/-38) km/s. The corresponding cosmic variance at these radii is 126(60)km/s, which implies that these estimated bulk flows are dominated by the data and not by the assumed prior model. The estimated bulk velocity is dominated by the data out to R~200 Mpc/h, where the cosmic variance on the individual Supergalactic Cartesian components (of the r.m.s. values) exceeds the variance of the Constrained Realizations by at least a factor of 2. The supergalactic SGX and SGY components of the CMB dipole velocity are recovered by the Wiener filter velocity field down to a very few km/s. The SGZ component of the estimated velocity, the one that is most affected by the Zone of Avoidance, is off by 126 km/s (an almost 2 sigma discrepancy).
In models of low-energy gauge mediation, the observed Higgs mass is in tension with the cosmological limit on the gravitino mass $m_{3/2} \lesssim 16$ eV. We present an alternative mediation mechanism of supersymmetry breaking via a $U(1)$ $D$-term with an $E_6$-inspired particle content, which we call "vector mediation". The gravitino mass can be in the eV range. The sfermion masses are at the 10 TeV scale, while gauginos around a TeV. This mechanism also greatly ameliorates the $\mu$-problem.
New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e., projected separations $<$30 kpc/h, and mass ratios less extreme than 4:1), while still having a sufficiently large angular separation that the VLA can spatially resolve both galaxies in the pair. Of the 34 galaxies, 17 are detected at $> 3\sigma$. We compare the HI gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated ($\sim 2.5\sigma$) with HI gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe.
We propose a classical SU(2) gauge field in a flavor-space locked configuration as a species of radiation in the early universe, and show that it would have a significant imprint on a primordial stochastic gravitational wave spectrum. In the flavor-space locked configuration, the electric and magnetic fields of each flavor are parallel and mutually orthogonal to other flavors, with isotropic and homogeneous stress-energy. Due to the non-Abelian coupling, the gauge field breaks the symmetry between left- and right-circularly polarized gravitational waves. This broken chiral symmetry results in a unique signal: non-zero cross correlation of the cosmic microwave background temperature and polarization, $TB$ and $EB$, both of which should be zero in the standard, chiral symmetric case. We forecast the ability of current and future CMB experiments to constrain this model. Furthermore, a wide range of behavior is shown to emerge, depending on the gauge field coupling, abundance, and allocation into electric and magnetic field energy density. The fluctuation power of primordial gravitational waves oscillates back and forth into fluctuations of the gauge field. In certain cases, the gravitational wave spectrum is shown to be suppressed or amplified by up to an order of magnitude depending on the initial conditions of the gauge field.
Recent work has demonstrated the potential of gravitationally lensed quasars to extend measurements of black hole spin out to high-redshift with the current generation of X-ray observatories. Here we present an analysis of a large sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with Chandra, utilizing over 1.6 Ms of total observing time, focusing on the rest-frame iron K emission from these sources. Although the X-ray signal-to-noise (S/N) currently available does not permit the detection of iron emission from the inner accretion disk in individual cases in our sample, we find significant structure in the stacked residuals. In addition to the narrow core, seen almost ubiquitously in local AGN, we find evidence for an additional underlying broad component from the inner accretion disk, with a clear red wing to the emission profile. Based on simulations, we find the detection of this broader component to be significant at greater than the 3-sigma level. This implies that iron emission from the inner disk is relatively common in the population of lensed quasars, and in turn further demonstrates that, with additional observations, this population represents an opportunity to significantly extend the sample of AGN spin measurements out to high-redshift.
In an attempt to place an explicit constraint on dark matter models, we define and estimate a mean surface density of a dark halo within a radius of maximum circular velocity, which is derivable for various galaxies with any dark-matter density profiles. We find that this surface density is generally constant across a wide range of maximum circular velocities of $\sim$ 10 to 400 km s$^{-1}$, irrespective of different density distribution in each of the galaxies. This common surface density at high halo-mass scales is found to be naturally reproduced by both cold and warm dark matter (CDM and WDM) models, even without employing any fitting procedures. However, the common surface density at dwarf-galaxy scales, for which we have derived from the Milky Way and Andromeda dwarf satellites, is reproduced only in a massive range of WDM particle masses, whereas CDM provides a reasonable agreement with the observed constancy. This is due to the striking difference between mass-concentration relations for CDM and WDM halos at low halo-mass scales. In order to explain the universal surface density of dwarf-galaxy scales in WDM models, we suggest that WDM particles need to be heavier than 3 keV.
Inspired by the $f(R)$ non-linear massive gravity, we propose a new kind of modified gravity model, namely $f(T)$ non-linear massive gravity, by adding the dRGT mass term reformulated in the vierbein formalism, to the $f(T)$ theory. We then investigate the cosmological evolution of $f(T)$ massive gravity, and constrain it by using the latest observational data. We find that it slightly favors a crossing of the phantom divide line from the quintessence-like phase ($w_{de} > -1$) to the phantom-like one ($w_{de} < -1$) as redshift decreases.
The accelerating expansion of the Universe points to a small positive value for the cosmological constant or vacuum energy density. We discuss recent ideas that the cosmological constant plus LHC results might hint at critical phenomena near the Planck scale.
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The observed high covering fractions of neutral hydrogen (HI) with column densities above $\sim 10^{17} \rm{cm}^{-2}$ around Lyman-Break Galaxies (LBGs) and bright quasars at redshifts z ~ 2-3 has been identified as a challenge for simulations of galaxy formation. We use the EAGLE cosmological, hydrodynamical simulation, which has been shown to reproduce a wide range of galaxy properties and for which the subgrid feedback was calibrated without considering gas properties, to study the distribution of HI around high-redshift galaxies. We predict the covering fractions of strong HI absorbers ($N_{\rm{HI}} \gtrsim 10^{17} \rm{cm}^{-2}$) inside haloes to increase rapidly with redshift but to depend only weakly on halo mass. For massive ($M_{200} \gtrsim 10^{12} {\rm M_{\odot}}$) halos the covering fraction profiles are nearly scale-invariant and we provide fitting functions that reproduce the simulation results. While efficient feedback is required to increase the HI covering fractions to the high observed values, the distribution of strong absorbers in and around halos of a fixed mass is insensitive to factor of two variations in the strength of the stellar feedback. In contrast, at fixed stellar mass the predicted HI distribution is highly sensitive to the feedback efficiency. The fiducial EAGLE simulation reproduces both the observed global column density distribution function of HI and the observed radial covering fraction profiles of strong HI absorbers around LBGs and bright quasars.
Massive bigravity, a theoretically consistent modification of general relativity with an additional dynamical rank two tensor, successfully describes the observed accelerated expansion of the Universe without a cosmological constant. Recent analyses of perturbations around a cosmological background have revealed power law instabilities in both scalar and tensor perturbations, motivating an analysis of the initial conditions, evolution, and cosmological observables to determine the viability of these theories. In this paper we focus on the tensor sector, and study a primordial stochastic gravitational wave background in massive bigravity. The phenomenology can differ from standard General Relativity due to non-trivial mixing between the two linearized tensor fluctuations in the theory, only one of which couples to matter. We study perturbations about two classes of cosmological solutions in bigravity, computing the tensor contribution to the temperature anisotropies in the Cosmic Microwave Background radiation and the present stochastic gravitational wave background. The result is strongly dependent on the choice of cosmological background and initial conditions. One class of background solution generically displaying tremendous growth in the amplitude of large-wavelength gravitational waves, while the other remains observationally indistinguishable from standard General Relativity for a wide variety of initial conditions. We analyze the initial conditions for tensor modes expected in an inflationary cosmology, finding again that there is a strong dependence on the assumed background. For one choice of background, the semi-classical theory is beyond the perturbative regime. For the other choice, inflation generically yields initial conditions that, when evolved, give rise to a stochastic background observationally indistinguishable from standard General Relativity.
Spectral distortions of the CMB have recently experienced an increased interest. One of the inevitable distortion signals of our cosmological concordance model is created by the cosmological recombination process, just a little before photons last scatter at redshift $z\simeq 1100$. These cosmological recombination lines, emitted by the hydrogen and helium plasma, should still be observable as tiny deviation from the CMB blackbody spectrum in the cm--dm spectral bands. In this paper, we present a forecast for the detectability of the recombination signal with future satellite experiments. We argue that serious consideration for future CMB experiments in space should be given to probing spectral distortions and, in particular, the recombination line signals. The cosmological recombination radiation not only allows determination of standard cosmological parameters, but also provides a direct observational confirmation for one of the key ingredients of our cosmological model: the cosmological recombination history. We show that, with present technology, such experiments are futuristic but feasible. The potential rewards won by opening this new window to the very early universe could be considerable.
In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACS J1206.2-0847, at z~0.44, probing its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme, sampling the cluster out to a radius ~2R200 (4 Mpc). We classify 412 galaxies as: passive, with strong Hdelta absorption (red and blue ones), and with emission lines from weak to very strong ones. A number of tests for substructure detection is applied to analyze the galaxy distribution in the velocity space, in the 2D space, and in the (3D) projected phase-space. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few, secondary, minor overdensities in 2D distribution. We detect no velocity gradient or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive and red strong Hdelta galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hdelta galaxies also mark a secondary, dense peak ~2 Mpc at ESE. The emission line galaxies cluster in several loose structures, mostly outside R200. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive and red strong Hdelta galaxies. The latter ones, interpreted as poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.
The standard cold dark matter (CDM) model predicts too many and too dense small structures. We consider an alternative model that the dark matter undergoes two-body decays with cosmological lifetime $\tau$ into only one type of massive daughters with non-relativistic recoil velocity $V_k$. This decaying dark matter model (DDM) can suppress the structure formation below its free-streaming scale at time scale comparable to $\tau$. Comparing with warm dark matter (WDM), DDM can better reduce the small structures while being consistent with high redshfit observations. We study the cosmological structure formation in DDM by performing self-consistent N-body simulations and point out that cosmological simulations are necessary to understand the DDM structures especially on non-linear scales. We propose empirical fitting functions for the DDM suppression of the mass function and the mass-concentration relation, which depend on the decay parameters lifetime $\tau$ and recoil velocity $V_k$, and redshift. The fitting functions lead to accurate reconstruction of the the non-linear power transfer function of DDM to CDM in the framework of halo model. Using these results, we set constraints on the DDM parameter space by demanding that DDM does not induce larger suppression than the Lyman-$\alpha$ constrained WDM models. We further generalize and constrain the DDM models to initial conditions with non-trivial mother fractions and show that the halo model predictions are still valid after considering a global decayed fraction. Finally, we point out that the DDM is unlikely to resolve the disagreement on cluster numbers between the Planck primary CMB prediction and the Sunyaev-Zeldovich (SZ) effect number count for $\tau \sim H_{0}^{-1}$.
We propose a procedure to evaluate the impact of nonlinear couplings on the evolution of massive neutrino streams in the context of large-scale structure growth. Such streams can be described by general nonlinear conservation equations, derived from a multiple-flow perspective, which generalize the conservation equations of non-relativistic pressureless fluids. The relevance of the nonlinear couplings is quantified with the help of the eikonal approximation applied to the subhorizon limit of this system. It highlights the role played by the relative displacements of different cosmic streams and it specifies, for each flow, the spatial scales at which the growth of structure is affected by nonlinear couplings. We found that, at redshift zero, such couplings can be significant for wavenumbers as small as $k=0.2\,h$/Mpc for most of the neutrino streams.
We investigate the effect of averaging inhomogeneities on expansion and large-scale structure growth observables using the exact and covariant framework of Macroscopic Gravity (MG). It is well-known that applying the Einstein's equations and spatial averaging do not commute and lead to the averaging problem. For the MG formalism applied to the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, this gives an extra dynamical term encapsulated as an averaging density parameter denoted $\Omega_A$. An exact isotropic cosmological solution of MG for the flat FLRW metric is already known in the literature, we derive here an anisotropic exact solution. Using the isotropic solution, we compare the expansion history to current data of distances to supernovae, Baryon Acoustic Oscillations, CMB last scattering surface, and Hubble constant measurements, and find $-0.05 \le \Omega_A \le 0.07$ (at the 95% CL). For the flat metric case this reduces to $-0.03 \le \Omega_A \le 0.05$. We also find that the inclusion of this term in the fits can shift the values of the usual cosmological parameters by a few to several percents. Next, we derive an equation for the growth rate of large scale structure in MG that includes a term due to the averaging and compare it to that of the LCDM concordance model. We find that an $\Omega_A$ of an amplitude range within the bounds above leads to a relative deviation of the growth from that of the LCDM of up to 2-4% at late times. Thus, the shift in the growth could be of comparable amplitude to that caused by similar changes in cosmological parameters like the dark energy density parameter or its equation of state. The effect could also be comparable in amplitude to some systematic effects considered for future surveys. This indicates that the averaging term and its possible effect need to be tightly constrained in future precision cosmological studies. (Abridged)
There has been a growing evidence for the existence of magnetic fields in the extra-galactic regions, while the attempt to associate their origin with the inflationary epoch alone has been found extremely challenging. We therefore take into account the consistent post-inflationary evolution of the magnetic fields that are originated from vacuum fluctuations during inflation. In the model of our interest, the electromagnetic (EM) field is coupled to a pseudo-scalar inflaton $\phi$ through the characteristic term $\phi F\tilde F$, breaking the conformal invariance. This interaction dynamically breaks the parity and enables a continuous production of only one of the polarization states of the EM field through tachyonic instability. The produced magnetic fields are thus helical. We find that the dominant contribution to the observed magnetic fields in this model comes from the modes that leave the horizon near the end of inflation, further enhanced by the tachyonic instability right after the end of inflation. The EM field is subsequently amplified by parametric resonance during the period of inflaton oscillation. Once the thermal plasma is formed (reheating), the produced helical magnetic fields undergo a turbulent process called inverse cascade, which shifts their peak correlation scales from smaller to larger scales. We consistently take all these effects into account within the regime where the perturbation of $\phi$ is negligible and obtain $B_{\rm eff} \sim 10^{-19}$G, indicating the necessity of additional mechanisms to accommodate the observations.
The relationship between the cosmic microwave background radiation temperature and the redshift, i.e., the $T$--$z$ relation, is examined in a phenomenological dissipative model. The model contains two constant terms, as if a nonzero cosmological constant $\Lambda$ and a dissipative process are operative in a homogeneous, isotropic, and spatially flat universe. The $T$--$z$ relation is derived from a general radiative temperature law, as appropriate for describing nonequilibrium states in a creation of cold dark matter (CCDM) model. Using this relation, the radiation temperature in the late universe is calculated as a function of a dissipation rate ranging from $\tilde{\mu} =0$, corresponding to a nondissipative $\Lambda$CDM model, to $\tilde{\mu} =1$, corresponding to a fully dissipative CCDM model. The $T$--$z$ relation for $\tilde{\mu} =0$ is linear for standard cosmology and is consistent with observations. However, with increasing dissipation rate $\tilde{\mu}$, the radiation temperature gradually deviates from a linear law because the effective equation-of-state parameter varies with time. When the background evolution of the universe agrees with a fine-tuned pure $\Lambda$CDM model, the $T$--$z$ relation for low $\tilde{\mu}$ matches observations, whereas the $T$--$z$ relation for high $\tilde{\mu}$ does not. Previous work also found that a weakly dissipative model accords with measurements of a growth rate for clustering related to structure formations. These results imply that low dissipation is likely for the universe.
A mostly right-handed sneutrino as the lightest supersymmetric particle (LSP) is an interesting dark matter candidate, leading to LHC signatures which can be quite distinct from those of the conventional neutralino LSP. Using SModelSv1.0.1 for testing the model against the limits published by ATLAS and CMS in the context of so-called Simplified Model Spectra (SMS), we investigate to what extent the supersymmetry searches at Run 1 of the LHC constrain the sneutrino-LSP scenario. Moreover, we discuss the most relevant topologies for which no SMS results are provided by the experimental collaborations but which would allow to put more stringent constraints on sneutrino LSPs. These include, for instance, the mono-lepton signature which should be particularly interesting to consider at Run 2 of the LHC.
The central image of a strongly lensed background source places constraints on the foreground lens galaxy's inner mass profile slope, core radius and mass of its nuclear supermassive black hole. Using high-resolution long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations and archival $Hubble~Space~Telescope$ ($HST$) imaging, we model the gravitational lens H-ATLAS J090311.6+003906 (also known as SDP.81) and search for the demagnified central image. There is central continuum emission from the lens galaxy's active galactic nucleus (AGN) but no evidence of the central lensed image in any molecular line. We use the CO $J$=5-4 map to determine the flux limit of the central image excluding the AGN continuum. We predict the flux density of the central image and use the limits from the ALMA data to constrain the inner mass distribution of the lens. For the core radius of $0.15"$ measured from $HST$ photometry of the lens galaxy assuming that the central flux is completely attributed to the AGN, we find that a black hole mass of $\mathrm{\log(M_{BH}/M_{\odot})} \gtrsim 8.4$ is preferred. Deeper observations with a detection of the central image will significantly improve the constraints of the inner mass distribution of the lens galaxy.
We generalize the technique of fringe-rate filtering, whereby visibilities measured by a radio interferometer are re-weighted according to their temporal variation. As the Earth rotates, radio sources traverse through an interferometer's fringe pattern at rates that depend on their position on the sky. Capitalizing on this geometric interpretation of fringe rates, we employ time-domain convolution kernels to enact fringe-rate filters that sculpt the effective primary beam of antennas in an interferometer. As we show, beam sculpting through fringe-rate filtering can be used to optimize measurements for a variety of applications, including mapmaking, minimizing polarization leakage, suppressing instrumental systematics, and enhancing the sensitivity of power-spectrum measurements. We show that fringe-rate filtering arises naturally in minimum variance treatments of many of these problems, enabling optimal visibility-based approaches to analyses of interferometric data that avoid systematics potentially introduced by traditional approaches such as imaging. Our techniques have recently been demonstrated in Ali et al. (2015), where new upper limits were placed on the 21 cm power spectrum from reionization, showcasing the ability of fringe-rate filtering to successfully boost sensitivity and reduce the impact of systematics in deep observations.
In this paper, we demonstrate that the Wald's entropy for any spherically symmetric blackhole within an infinite derivative theory of gravity is determined solely by the area law. Thus, the infrared behaviour of gravity is captured by the Einstein-Hilbert term, provided that the massless graviton remains the only propagating degree of freedom in the spacetime.
Tip of the red giant branch measurements based on Hubble Space Telescope and ground-based imaging have resulted in accurate distances to 29 galaxies in the nearby Centaurus A Group. All but two of the 29 galaxies lie in either of two thin planes roughly parallel with the supergalactic equator. The planes are only slightly tilted from the line-of-sight, leaving little ambiguity regarding the morphology of the structure. The planes have characteristic r.m.s. long axis dimensions of ~300 kpc and short axis dimensions of ~60 kpc, hence axial ratios ~0.2, and are separated in the short axis direction by 303 kpc.
We survey a variety of cosmological problems where the issue of generality has arisen. This is aimed at providing a wider context for many claims and deductions made when philosophers of science choose cosmological problems for investigation. We show how simple counting arguments can be used to characterise parts of the general solution of Einstein's equations when various matter fields are present and with different spatial topologies. Applications are described to the problem of singularities, static cosmological models, cosmic no hair theorems, the late-time isotropisation of cosmological models, and the number of parameters needed to describe a general astronomical universe.
A general method to extract exact cosmological solutions for scalar field dark energy in the presence of perfect fluids is presented. We use as a selection rule the existence of invariant transformations for the Wheeler De Witt (WdW) equation. We show that the existence of point transformation in which the WdW equation is invariant is equivalent to the existence of conservation laws for the field equations. Mathematically, the existence of extra integrals of motion indicates the existence of analytical solutions. We extend previous work by providing exact solutions for the Hubble parameter and the effective dark energy equation of state parameter for cosmologies containing a combination of perfect fluid and a scalar field whose self-interaction potential is a power of hyperbolic functions. Finally, we perform a dynamical analysis by studying the fixed points of the field equations using dimensionless variables. Amongst the variety of dynamical cases, we find that if the current cosmological model is Liouville integrable (admits conservation laws) then there is a unique stable point which describes the de-Sitter phase of the universe.
We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (L_IR~10^13 L_sun) with strong radio emission (L_1.4GHz~10^25 W/Hz) at z=2.553. The source was identified in the citizen science project SpaceWarps through the visual inspection of tens of thousands of iJKs colour composite images of Luminous Red Galaxies (LRGs), groups and clusters of galaxies and quasars. Appearing as a partial Einstein ring (r_e~3") around an LRG at z=0.2, the galaxy is extremely bright in the sub-millimetre for a cosmological source, with the thermal dust emission approaching 1 Jy at peak. The redshift of the lensed galaxy is determined through the detection of the CO(3-2) molecular emission line with the Large Millimetre Telescope's Redshift Search Receiver and through [OIII] and H-alpha line detections in the near-infrared from Subaru/IRCS. We have resolved the radio emission with high resolution (300-400 mas) eMERLIN L-band and JVLA C-band imaging. These observations are used in combination with the near-infrared imaging to construct a lens model, which indicates a lensing magnification of ~10x. The source reconstruction appears to support a radio morphology comprised of a compact (<250 pc) core and more extended component, perhaps indicative of an active nucleus and jet or lobe.
We consider Supersymmetric (SUSY) and non-SUSY models of chaotic inflation based on the phi^n potential with 2<=n<=6. We show that the coexistence of a nonminimal coupling to gravity, fR=1+cR phi^{n/2}, with a kinetic mixing of the form fK=cK fR^m can accommodate values of the spectral index, ns, and the tensor-to-scalar ratio, r, favored by the Bicep2/Keck Array and Planck results for 0<=m<=4 and 2.5x10^{-4}<=rRK=cR/cK^{n/4}<=1. Inflation can be attained for subplanckian inflaton values with the corresponding effective theories retaining the perturbative unitarity up to the Planck scale.
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