arXiv: 26 December 2011

 Formation of primordial black holes from non-Gaussian perturbations produced in waterfall transition

Authors: Edgar Bugaev, Peter Klimai

arXiv:1112.5601v1

 We consider the process of primordial black hole (PBH) formation originated from primordial curvature perturbations produced during waterfall transition (with tachyonic instability), at the end of hybrid inflation. It is known that in such inflation models, rather large values of curvature perturbation amplitudes can be reached, which can potentially cause a significant PBH production in the early Universe. The probability distributions of density perturbation amplitudes in this case can be strongly non-Gaussian, which requires a special treatment. We calculated PBH abundances and PBH mass spectra for the model, and analyzed their dependence on model parameters. We obtained the constraints on the parameters of the inflationary potential, using the available limits on $\beta_{PBH}$.

 

 Dark Matter Halo Profiles of Massive Clusters: Theory vs. Observations

Authors: Suman Bhattacharya, Salman Habib, Katrin Heitmann (Argonne/ KICP/ U. Chicago)

arXiv:1112.5479v1

 We study dark matter halo profiles using a suite of numerical simulations. We carry out (gravity-only) simulations of the current concordance LCDM cosmology, covering a halo mass range of 2.10^(12) to 2.10^(15) solar masses and a redshift range of z=0-2, dictated primarily by cluster observation considerations. We find that the shape of the concentration-mass (c-M) relation flattens at high redshift and this flattening of the slope is naturally expressed if c is written as a function of the peak height parameter, \nu. Although the logarithmic slope of the c-M relation changes with redshift, that of the (c-\nu) relation is effectively constant over the redshift range z=0-2. The amplitude of c(\nu) varies by about 30% from z=0-2 over the mass range for massive clusters. The (c-\nu) relation is, however, not universal. We use a large suite of simulations covering the currently allowed wCDM parameter space and show that the (c-\nu) relation varies by about +/- 20 % when cosmological parameters are varied. We find that the distribution of the concentrations can be well-fit by a Gaussian with variance, \sigma_c=0.33c, where the ratio of the variance to the mean, \sigma_c/c, is independent of the radius at which the concentration is defined, the dynamical state of the halo, and the underlying cosmology. We compare our simulation predictions with current results obtained from (primarily low) redshift observations and find good agreement with the observational data for massive clusters of mass > 4.10^(14) solar masses, but there are disagreements at lower masses. Because of uncertainty in observational systematics and modeling of baryonic physics, the significance of these discrepancies remains to be understood. (Abridged)

 

 

arXiv: 23 December 2011

 Cosmological Constraints from Sunyaev-Zel'dovich-Selected Clusters with X-ray Observations in the First 178 Square Degrees of the South Pole Telescope Survey

Authors: B. A. Benson, T. de Haan, J. P. Dudley, C. L. Reichardt, K. A. Aird, K. Andersson, R. Armstrong, M. Bautz, M. Bayliss, G. Bazin, L. E. Bleem, M. Brodwin, J. E. Carlstrom, C. L. Chang, H. M. Cho, A. Clocchiatti, T. M. Crawford, A. T. Crites, S. Desai, M. A. Dobbs, R. J. Foley, W. R. Forman, E. M. George, M. D. Gladders, N. W. Halverson, F. W. High, G. P. Holder, W. L. Holzapfel, S. Hoover, J. D. Hrubes, C. Jones, M. Joy, R. Keisler, L. Knox, A. T. Lee, E. M. Leitch, J. Liu, M. Lueker, D. Luong-Van, A. Mantz, D. P. Marrone, M. McDonald, J. J. McMahon, J. Mehl, S. S. Meyer, L. Mocanu, J. J. Mohr, T. E. Montroy, S. S. Murray, T. Natoli, S. Padin, T. Plagge, C. Pryke, A. Rest, J. Ruel, J. E. Ruhl, B. R. Saliwanchik, A. Saro, K. K. Schaffer, L. Shaw, E. Shirokoff, J. Song, H. G. Spieler, B. Stalder,

Z. Staniszewski, A. A. Stark, K. Story, C. W. Stubbs, R. Suhada, A. van Engelen, K. Vanderlinde, J. D. Vieira, A. Vikhlinin, R. Williamson, O. Zahn, A. Zenteno

et al. (12 additional authors not shown)

arXiv:1112.5435v1

 We use measurements from the South Pole Telescope (SPT) Sunyaev Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg2 of the 2500 deg2 SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM. Assuming a spatially flat LCDM cosmological model, we find the SPT cluster sample constrain sigma_8 (Omega_m/0.25)^0.30 = 0.785 +- 0.037. In combination with measurements of the CMB power spectrum from the SPT and the seven-year WMAP data, the SPT cluster sample constrain sigma_8 = 0.795 +- 0.016 and Omega_m = 0.255 +- 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the LCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (sum mnu), the effective number of relativistic species (Neff), and a primordial non-Gaussianity (fNL). We find that adding the SPT cluster data significantly improves the constraints on w and sum mnu beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w=-0.973 +- 0.063 and the sum of neutrino masses sum mnu < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. [abbrev.]

 

 The shapes of Milky Way satellites: looking for signatures of tidal stirring

Authors: Ewa L. Lokas, Steven R. Majewski, Stelios Kazantzidis, Lucio Mayer, Jeffrey L. Carlin, David L. Nidever, Leonidas A. Moustakas

arXiv:1112.5336v1

 We study the shapes of Milky Way satellites in the context of the tidal stirring scenario for the formation of dwarf spheroidal galaxies. The standard procedures used to measure shapes involve smoothing and binning of data and thus may not be sufficient to detect subtle structural properties like bars. Taking advantage of the fact that in nearby dwarfs photometry of individual stars is available we introduce discrete measures of shape based on the two-dimensional inertia tensor and the Fourier bar mode. We apply these measures of shape first to a variety of simulated dwarf galaxies formed via tidal stirring of disks embedded in dark matter halos and orbiting the Milky Way. In addition to strong mass loss and randomization of stellar orbits, the disks undergo morphological transformation which typically involves the formation of a triaxial bar after the first pericenter passage. These tidally induced bars persist for a few Gyr before being shortened towards a more spherical shape if the tidal force is strong enough. We test this prediction by measuring in a similar way the shape of nearby dwarf galaxies, satellites of the Milky Way. We detect inner bars in Ursa Minor, Sagittarius, LMC and possibly Carina. In addition, six out of eleven studied dwarfs show elongated stellar distributions in the outer parts which may signify transition to the tidal tails. We thus find the shapes of Milky Way satellites to be consistent with the predictions of the tidal stirring model.

 

Standard Model false vacuum Inflation: correlating the tensor-to-scalar ratio to the top and Higgs masses

Authors: Isabella Masina, Alessio Notari

arXiv:1112.5430v1

For a narrow band of values of the top quark and Higgs boson masses, the Standard Model Higgs potential develops a false minimum at energies of about $10^{16}$ GeV, where primordial Inflation could have happened. A graceful exit to a radiation dominated era is provided e.g. by scalar-tensor gravity models. We pointed out that if Inflation happened in this false minimum, the Higgs boson mass has to be in the range $126.0 \pm 3.5$ GeV, where ATLAS and CMS subsequently reported excesses of events. Here we show that for these values of the Higgs mass, the inflationary gravitational wave background has be discovered with a tensor-to-scalar ratio at hand of future experiments. We suggest that combining cosmological observations with measurements of the top and Higgs masses represents a further test of the hypothesis that the Standard Model false minimum was the source of Inflation in the Universe.

 

 

arXiv: 22 December 2011

 An Anomaly in the Angular Distribution of Quasar Spectra

Authors: Michael J. Longo

arXiv:1112.5045v1

 Quasars provide our most distant view of the Universe. The Sloan Survey now contains over 100,000 quasar candidates. A careful look at the angular distribution of quasar spectra shows a surprising blue shift toward (alpha, delta) ~ (190{\deg}, 0{\deg}). The angular distribution of the shift appears to be consistent with a large peculiar velocity toward that direction. However, the size of the shift would suggest our peculiar velocity is ~0.2 c, which is two orders of magnitude larger than measures of our peculiar velocity from nearby galaxies and cosmic microwave background (CMB) measurements. It is too large to explain as a systematic error in the quasar magnitudes. The direction is consistent with that of the reported anomalies in the CMB, the so-called "axis of evil". The angular pattern of the blue shift appears to be consistent with the existence of an expanding bubble universe in that direction, which could also explain the CMB anomalies.

 

 

 The WiggleZ Dark Energy Survey: Cosmological neutrino mass constraint from blue high-redshift galaxies

Authors: Signe Riemer--Sørensen, Chris Blake, David Parkinson, Tamara M. Davis, Sarah Brough, Matthew Colless, Carlos Contreras, Warrick Couch, Scott Croom, Darren Croton, Michael J. Drinkwater, Karl Forster, David Gilbank, Mike Gladders, Karl Glazebrook, Ben Jelliffe, Russell J. Jurek, I-hui Li, Barry Madore, D. Christopher Martin, Kevin Pimbblet, Gregory B. Poole, Michael Pracy, Rob Sharp, Emily Wisnioski, David Woods, Ted K. Wyder, H.K.C. Yee

arXiv:1112.4940v1

 The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematics from non-linear structure formation, redshift-space distortions and galaxy bias than previous surveys. We obtain a upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.

 

 Primordial Magnetic Field Effects on the CMB and Large Scale Structure

Authors: Dai G. Yamazaki, Kiyotomo Ichiki, Toshitaka Kajino, Grant J. Mathew

arXiv:1112.4922v1

 Magnetic fields are everywhere in nature and they play an important role in every astronomical environment which involves the formation of plasma and currents. It is natural therefore to suppose that magnetic fields could be present in the turbulent high temperature environment of the big bang. Such a primordial magnetic field (PMF) would be expected to manifest itself in the cosmic microwave background (CMB) temperature and polarization anisotropies, and also in the formation of large- scale structure. In this review we summarize the theoretical framework which we have developed to calculate the PMF power spectrum to high precision. Using this formulation, we summarize calculations of the effects of a PMF which take accurate quantitative account of the time evolution of the cut off scale. We review the constructed numerical program, which is without approximation, and an improvement over the approach used in a number of previous works for studying the effect of the PMF on the cosmological perturbations. We demonstrate how the PMF is an important cosmological physical process on small scales. We also summarize the current constraints on the PMF amplitude $B_\lambda$ and the power spectral index $n_B$ which have been deduced from the available CMB observational data by using our computational framework.

 

 New Constraints on Isospin-Violating Dark Matter

Authors: Jason Kumar, David Sanford, Louis E. Strigari

arXiv:1112.4849v1

 We derive bounds on the dark matter annihilation cross-section for low-mass (5-20 GeV) dark matter annihilating primarily to up or down quarks, using the Fermi-LAT bound on gamma-rays from Milky Way satellites. For models in which dark matter-Standard Model interactions are mediated by particular contact operators, we show that these bounds can be directly translated into bounds on the dark matter-proton scattering cross-section. For isospin-violating dark matter, these constraints are tight enough to begin to constrain the parameter-space consistent with experimental signals of low-mass dark matter. We discuss possible models that can evade these bounds.

 

 

arXiv: 21 December 2011

 Nonlinear cosmological consistency relations and effective matter stresses

Authors: Guillermo Ballesteros, Lukas Hollenstein, Rajeev Kumar Jain, Martin Kunz

arXiv:1112.4837v1

 We propose a completely nonlinear framework to construct consistency relations for testing generic cosmological scenarios using the evolution of large scale structure. It is based on the covariant approach in combination with a frame that is purely given by the metric, the normal frame. As an example, we apply this framework to the LCDM model, extending the usual first order conditions on the metric potentials to second order. We argue that working in the normal frame is not only a practical choice but one that closely resembles our actual situation as observers. In this frame, effective pressures and anisotropic stresses appear at second order in perturbation theory, even for dust. We quantify this effect and compare it, for illustration, with the pressure of a generic clustering dark energy fluid and the anisotropic stress in the DGP model. Besides, we also discuss the effect of a mismatch of the potentials on the determination of galaxy bias.

 

 The Fine-Tuning of the Universe for Intelligent Life

Authors: Luke A. Barnes

arXiv:1112.4647v1

 The fine-tuning of the universe for intelligent life has received a great deal of attention in recent years, both in the philosophical and scientific literature. The claim is that in the space of possible physical laws, parameters and initial conditions, the set that permits the evolution of intelligent life is very small. I present here a review of the scientific literature, outlining cases of fine-tuning in the classic works of Carter, Carr and Rees, and Barrow and Tipler, as well as more recent work. To sharpen the discussion, the role of the antagonist will be played by Victor Stenger's recent book The Fallacy of Fine-Tuning: Why the Universe is Not Designed for Us. Stenger claims that all known fine-tuning cases can be explained without the need for a multiverse. Many of Stenger's claims will be found to be highly problematic. We will touch on such issues as the logical necessity of the laws of nature; objectivity, invariance and symmetry; theoretical physics and possible universes; entropy in cosmology; cosmic inflation and initial conditions; galaxy formation; the cosmological constant; stars and their formation; the properties of elementary particles and their effect on chemistry and the macroscopic world; the origin of mass; grand unified theories; and the dimensionality of space and time. I also provide an assessment of the multiverse, noting the significant challenges that it must face. I do not attempt to defend any conclusion based on the fine-tuning of the universe for intelligent life. This paper can be viewed as a critique of Stenger's book, or read independently.

arXiv: 20 December 2011

Cosmic shear bispectrum from second-order perturbations in General Relativity

Authors: Francis Bernardeau, Camille Bonvin, Nicolas Van de Rijt, Filippo Vernizzi

arXiv:1112.4430v1

Future lensing surveys will be nearly full-sky and reach an unprecedented depth, probing scales closer and closer to the Hubble radius. This motivates the study of the cosmic shear beyond the small-angle approximation and including general relativistic corrections that are usually suppressed on sub-Hubble scales. The complete expression of the reduced cosmic shear at second order including all relativistic effects was derived in [1]. In the present paper we compute the resulting cosmic shear bispectrum when all these effects are properly taken into account and we compare it to primordial non-Gaussianity of the local type. The new general relativistic effects are generically smaller than the standard non-linear couplings. However, their relative importance increases at small multipoles and for small redshifts of the sources. The dominant effect among these non standard corrections is due to the inhomogeneity of the source redshift. In the squeezed limit, its amplitude can become of the order of the standard couplings when the redshift of the sources is below 0.5. Moreover, while the standard non-linear couplings depend on the angle between the short and long mode, the relativistic corrections do not and overlap almost totally with local type non-Gaussianity. We find that they can contaminate the search for a primordial local signal by f_NL>10.

 

 Comment on "The Real Problem with MOND" by Scott Dodelson, arXiv:1112.1320

Authors: J. W. Moffat, V. T. Toth

arXiv:1112.4386v1

We comment on arXiv:1112.1320 and point out that baryonic oscillations of the matter power spectrum, while predicted by theories that do not incorporate collisionless cold dark matter, are strongly suppressed by the statistical window function that is used to process finite-sized galaxy samples. We assert that with present-day data sets, the slope of the matter power spectrum is a much stronger indicator of a theory's validity. We also argue that MOND should not be used as a strawman theory as it is not in general representative of modified gravity theories; some theories, notably our scalar-vector-tensor MOdified Gravity (MOG), offer much more successful predictions of cosmological observations.

 

 The Statistics of Cosmological Lyman-alpha Absorption

Authors: Dipak Munshi, Peter Coles, Matteo Viel

arXiv:1112.4334v1

We study the effect of the non-Gaussianity induced by gravitational evolution upon the statistical properties of absorption in quasar (QSO) spectra. Using the generic hierarchical ansatz and the lognormal approximation we derive the analytical expressions for the one-point PDF as well as for the joint two-point probability distribution (2PDF) of transmitted fluxes in two neighbouring QSOs. These flux PDFs are constructed in 3D as well as in projection (i.e. in 2D). The PDFs are constructed by relating the lower-order moments, i.e. cumulants and cumulant correlators, of the fluxes to the 3D neutral hydrogen distribution which is, in turn, expressed as a function of the underlying dark matter distribution. The lower-order moments are next modelled using a generating function formalism in the context of a {\em minimal tree-model} for the higher-order correlation hierarchy. These different approximations give nearly identical results for the range of redshifts probed, and we also find a very good agreement between our predictions and outputs of hydrodynamical simulations. The formalism developed here for the joint statistics of flux-decrements concerning two lines of sight can be extended to multiple lines of sight, which could be particularly important for the 3D reconstruction of the cosmic web from QSO spectra (e.g. in the BOSS survey). These statistics probe the underlying projected neutral hydrogen field and are thus linked to "hot-spots" of absorption. The results for the PDF and the bias presented here use the same functional forms of scaling functions that have previously been employed for the modelling of other cosmological observation such as the Sunyaev-Zel'dovich effect.

 

What Do Dark Matter Properties Tell Us About Their Mass Assembly Histories?

Authors: Anson W. C. Wong, James E. Taylor

arXiv:1112.4229v1

 Individual dark matter halos in cosmological simulations vary widely in their detailed structural properties such as shape, rotation, substructure and degree of internal relaxation. Recent non-parametric (principal component) analyses suggest that a few principal components explain a large fraction of the scatter in halo properties. The main principal component is closely linked with concentration, which in turn is known to be related to the mass accretion history of the halo. Here we examine more generally the connection between mass accretion history and structural parameters. The space of mass accretion histories has principal components of its own. We find that the strongest two can be interpreted as the overall age of the halo and the acceleration or deceleration of growth at late times. These two components only account for $\sim70$%\ of the scatter in mass accretions histories however, due to the stochastic effect of major mergers. Relating structural parameters to formation history, we find that concentration correlates strongly with the early history of the halo, while relaxation correlates with the late history. We examine the inferences about formation history that can be drawn by splitting haloes into subsamples, based on observable properties such as concentration and shape at some final time. This approach suggests interesting possibilities, such as the possibility of defining young and old samples of galaxy clusters in a rigorous, quantitative way, or testing the dynamical assumptions of galaxy formation models empirically.

 

 Modified Newtonian Dynamics: A Review

Authors: Benoit Famaey, Stacy McGaugh

arXiv:1112.3960v1

 A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i) there is a vast amount of unseen mass in some novel form - dark matter - or (ii) the data indicate a breakdown of our understanding of gravity on the relevant scales, or (iii) both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of any alternative theoretical framework. We then show that many of these puzzling observations can be summarized by one single scaling relation - Milgrom's law - involving an acceleration constant (or a characteristic surface density) of the order of the square-root of the cosmological constant in natural units. This relation can at present most easily be interpreted as the effect of a single universal force law resulting from a modification of Newtonian dynamics (MOND) on galactic scales. We exhaustively review the current observational successes and problems of this alternative paradigm at all astrophysical scales, and summarize the various theoretical attempts (TeVeS, GEA, BIMOND, and others) made to effectively embed this modification of Newtonian dynamics within a generally covariant theory of gravity.

 

 

arXiv: 19 December 2011

 Inflationary magnetic fields spoil the homogeneity and isotropy of the Universe

Authors: Camille Bonvin, Chiara Caprini, Ruth Durrer

arXiv:1112.3897v1

 We show that magnetic fields generated during inflation gives rise to a constant mode in the Bardeen potential after inflation, in the radiation era, which is proportional to the magnetic scalar anisotropic stress. The ratio of this constant mode of the Bardeen potential to the background curvature grows in the radiation era, with the fatal consequence of spoiling the homogeneity and isotropy of the Friedmann Lemaitre (FL) Universe. This happens even if back-reaction on the background metric is negligible during inflation, and severely constrains magnetogenesis mechanisms operating during inflation.

 

 

arXiv: 16 December 2011

Vacuum Structure and the Arrow of Time

Authors: Raphael Bousso

arXiv:1112.3341v1

 We find ourselves in an extended era of entropy production. Unlike most other observations, the arrow of time is usually regarded as a constraint on initial conditions. I argue, however, that it primarily constrains the vacuum structure of the theory. I exhibit simple scalar field potentials in which low-entropy initial conditions are not necessary, or not sufficient, for an arrow of time to arise. I argue that the string theory landscape gives rise to an arrow of time independently of the initial entropy, assuming a plausible condition on the lifetime of its metastable vacua. In particular, a theory of initial conditions that favors large initial entropy, such as the Hartle-Hawking proposal, is not ruled out by observation. The dynamical resolution of the arrow of time problem arises from the same structural properties of the string landscape that allow it to solve the cosmological constant problem without producing an empty universe, particularly its high dimensionality and the large difference in vacuum energy between neighboring vacua.

 

Cycles in the Multiverse

Authors: Matthew C. Johnson, Jean-Luc Lehners

arXiv:1112.3360v1

 Eternal inflation is a seemingly generic consequence of theories that give rise to accelerated expansion of the universe and possess multiple vacuum states. Making predictions in an eternally inflating universe is notoriously difficult because one must compare infinite quantities, and a wide variety of regulating procedures yield radically different results. This is the measure problem of eternal inflation. In this paper, we analyze models of eternal inflation which allow for the possibility of cyclic bubble universes: in each bubble, standard cosmological evolution is re-played over and over again. Eternal inflation can generically arise in cyclic models that include a dark energy dominated phase. In such models, several problematic consequences of standard regulating procedures, such as the youngness and Boltzmann Brain problems, are substantially alleviated. We discuss the implications for making predictions in cyclic models, as well as some general implications for understanding the measure problem in eternal inflation.

 

 

 

arXiv: 15 December 2011

 Seeing in the dark -- II. Cosmic shear in the Sloan Digital Sky Survey

Authors: Eric M. Huff, Tim Eifler, Christopher M. Hirata, Rachel Mandelbaum, David Schlegel, Uros Seljak

arXiv:1112.3143v1

 Statistical weak lensing by large-scale structure -- cosmic shear -- is a promising cosmological tool, which has motivated the design of several large upcoming surveys. Here, we present a measurement of cosmic shear using coadded Sloan Digital Sky Survey (SDSS) imaging in 168 square degrees of the equatorial region, with r<23.5 and i<22.5, a source number density of 2.2 galaxies per square arcminute and median redshift of 0.52. These coadds were generated using a new method described in the companion Paper I that was intended to minimise systematic errors in the lensing measurement due to coherent PSF anisotropies that are otherwise prevalent in the SDSS imaging data. We present measurements of cosmic shear out to angular separations of 2 degrees, along with systematics tests that (combined with those from Paper I on the catalogue generation) demonstrate that our results are dominated by statistical rather than systematic errors. Assuming a cosmological model corresponding to WMAP7 and allowing only the amplitude of matter fluctuations to vary, we find a best-fit value of sigma_8=0.636 +0.109 -0.154 (1-sigma); without systematic errors this would be sigma_8=0.636 +0.099 -0.137 (1-sigma). Assuming a flat LCDM model, the combined constraints with WMAP7 are sigma_8=0.784 +0.028 -0.026 (1-sigma), +0.055 -0.054 (2-sigma) and Omega_m h^2=0.1303 +0.0047 -0.0048 (1-sigma)+0.009 -0.009 (2-sigma); the 2-sigma error ranges are respectively 14 and 17 per cent smaller than WMAP7 alone. Aside from the intrinsic value of such cosmological constraints from the growth of structure, we identify some important lessons for upcoming surveys that may face similar issues when combining multi-epoch data to measure cosmic shear.

 

 Surface mass density of the Einasto family of dark matter haloes: Are they Sersic-like?

Authors: Barun Kumar Dhar (1), Liliya L.R. Williams (1) ((1) School of Physics and Astronomy, University of Minnesota, Minneapolis, USA)

arXiv:1112.3116v1

Recent advances in N-body simulations of dark matter halos have shown that three-parameter models, in particular the Einasto profile characterized by d ln {\rho}(r)/d ln r / r with a shape parameter {\alpha} < 0.3, are able to produce better fits to the 3D spatial density profiles than two-parameter models like the Navarro, Frenk and White (NFW), and Moore et al. profiles.
In this paper, we present for the first time an analytically motivated form for the 2D surface mass density of the Einasto family of dark matter haloes, in terms of the 3D spatial density parameters for a wide range of the shape parameter 0.1 < {\alpha} < 1. Our model describes a projected (2D) Einasto profile remarkably well between 0 and (3 - 5) r_{200}, with errors less than 0.3 per cent for {\alpha} < 0.3 and less than 2 per cent for {\alpha} as large as 1. This model (in 2D) can thus be used to fit strong and weak lensing observations of galaxies and clusters whose total spatial (3D) density distributions are believed to be Einasto-like. Further, given the dependence of our model on the 3D parameters, one can reliably estimate structural parameters of the spatial (3D) density from 2D observations. We also consider a Sersic-like parametrization for the above family of projected Einasto profiles and observe that fits with a Sersic profile are sensitive to whether one fits the projected density in linear scale or logarithmic scale and yield widely varying results. Structural parameters of Einasto-like systems, inferred from fits with a Sersic profile, should be used with caution.

 

 

arXiv: 14 December 2011

 The Impact of Assuming Flatness in the Determination of Neutrino Properties from Cosmological Data

Authors: Aaron Smith, Maria Archidiacono, Asantha Cooray, Francesco De Bernardis, Alessandro Melchiorri, Joseph Smidt

arXiv:1112.3006v1

 Recent cosmological data have provided new constraints on the number of neutrino species and on the neutrino mass. However these constraints depend on assumptions related to the underlying cosmology. Since a correlation is expected between the number of effective neutrinos, N_{eff}, the neutrino mass \sum M_\nu, and the curvature of the universe, \Omega_k, it is useful to investigate the current constraints in the framework of a non-flat universe. In this paper we update the constraints on neutrino parameters by making use of the latest Cosmic Microwave Background (CMB) data from the ACT and SPT experiments and consider the possibility of a universe with non-zero curvature. We first find a negative correlation between curvature and N_{eff} with a correlation coefficient of -0.36 and we place new constraints on N_{eff} and \Omega_k, with N_{eff} = 4.03 +/- 0.45 and 10^3, \Omega_k = -4.46 +/- 5.24. Thus, even when \Omega_k is allowed to vary, N_{eff} = 3 is still disfavored at 95% confidence. The correlation between neutrino mass and curvature is much stronger, with a correlation coefficient of 0.78 that shifts the 95% upper limit of \sum M_\nu < 0.446 eV to \sum M_\nu < 0.948 eV. Thus, the impact of assuming flatness in neutrino cosmology is significant and an essential consideration with future experiments.

 

  Is Dark Energy Falsifiable?

Authors: Carl H. Gibson (University of California at San Diego), Rudolph E. Schild (Harvard University)

arXiv:1112.2758v1

 Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti-gravitational dark energy material driving the accelerating expansion of the universe also true? To be physically useful these propositions must be falsifiable; that is, subject to observational tests that could render them false, and both fail when viscous, diffusive, astro-biological and turbulence effects are included in the interpretation of observations. A more plausible explanation of negative stresses producing the big bang is turbulence at Planck temperatures. Inflation results from gluon viscous stresses at the strong force transition. Anti-gravitational (dark energy) turbulence stresses are powerful but only temporary. No permanent dark energy is needed. At the plasma-gas transition, viscous stresses cause fragmentation of plasma proto-galaxies into dark matter clumps of primordial gas planets, each of which falsifies dark-energy cold-dark-matter cosmologies. Clumps of these planets form all stars, and explain the alleged accelerating expansion of the universe as a systematic dimming error of Supernovae Ia by light scattered in the hot turbulent atmospheres of evaporated planets surrounding central white dwarf stars.

arXiv: 12 December 2011

The Paths of Gravity in Galileon Cosmology

Authors: Stephen A. Appleby, Eric V. Linder

arXiv:1112.1981v1

Galileon gravity offers a robust gravitational theory for explaining cosmic acceleration, having a rich phenomenology of testable behaviors. We explore three classes of Galileon models -- standard uncoupled, and linearly or derivatively coupled to matter -- investigating the expansion history with particular attention to early time and late time attractors, as well as the linear perturbations. From the relativistic and nonrelativistic Poisson equations we calculate the generalizations of the gravitational strength (Newton's constant), deriving its early and late time behavior. By scanning through the parameters we derive distributions of the gravitational strength at various epochs and trace the paths of gravity in its evolution. Using ghost-free and stability criteria we restrict the allowed parameter space, finding in particular that the linear and derivative coupled models are severely constrained by classical instabilities in the early universe.

 

 

What if ... General Relativity is not the theory?

Authors: Orfeu Bertolami

arXiv:1112.2048v1

 The nature of gravity is fundamental to understand the scaffolding of the Universe and its evolution. Einstein's general theory of relativity has been scrutinized for over ninety five years and shown to describe accurately all phenomena from the solar system to the Universe. However, this success is achieved in the case of the largest scales provided one admits contributions to energy-momentum tensor involving dark components such as dark energy and dark matter. Moreover, the theory has well known shortcomings, such as the problem of singularities, the cosmological constant problem and the well known initial conditions problems for the cosmological description. Furthermore, general relativity also does not fit the well known procedures that allow for the quantization of the other fundamental interactions. In this discussion we briefly review the experimental bounds on the foundational principles of general relativity, and present three recent proposals to extend general relativity or, at least, to regard it under different perspectives.

 

What Drives the Growth of Black Holes?

Authors: David M. Alexander (Durham), Ryan C. Hickox (Durham, Dartmouth)

arXiv:1112.1949v1

 Massive black holes (BHs) are at once exotic and yet ubiquitous, residing in the centers of massive galaxies in the local Universe. Recent years have seen remarkable advances in our understanding of how these BHs form and grow over cosmic time, during which they are revealed as active galactic nuclei (AGN). However, despite decades of research, we still lack a coherent picture of the physical drivers of BH growth, the connection between the growth of BHs and their host galaxies, the role of large-scale environment on the fueling of BHs, and the impact of BH-driven outflows on the growth of galaxies. In this paper we review our progress in addressing these key issues, motivated by the science presented at the "What Drives the Growth of Black Holes?" workshop held at Durham on 26th-29th July 2010, and discuss how these questions may be tackled with current and future facilities

 

 

arXiv: 9 December 2011

Constraints on the CMB temperature redshift dependence from SZ and distance measurements

Authors: A. Avgoustidis, G. Luzzi, C. J. A. P. Martins, A. M. R. V. L. Monteiro

arXiv:1112.1862v1

The relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)$ is a key prediction of standard cosmology, but is violated in many non-standard models. Constraining possible deviations to this law is an effective way to test the $\Lambda$CDM paradigm and search for hints of new physics. We present state-of-the-art constraints, using both direct and indirect measurements. In particular, we point out that in models where photons can be created or destroyed, not only does the temperature-redshift relation change, but so does the distance duality relation, and these departures from the standard behaviour are related, providing us with an opportunity to improve constraints. We show that current datasets limit possible deviations of the form $T_{CMB}(z)=T_0(1+z)^{1-\beta}$ to be $\beta=0.004\pm0.016$ up to a redshift $z\sim 3$. We also discuss how, with the next generation of space and ground-based experiments, these constraints can be improved by more than one order of magnitude.

 

 The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space study

Authors: Andrei Mesinger, Matthew McQuinn, David Spergel

arXiv:1112.1820v1

 [ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel'dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time. Indeed, recent SPT measurements place a bound on the dimensionless kSZ power spectrum around a multipole of l=3000 of P_tot < 2.8 (6) micro K^2 at 95% C.L., by ignoring (allowing) correlations between the thermal Sunyaev-Zel'dovich (tSZ) effect and the cosmic infrared background (CIB). To interpret these and upcoming observations, we compute the kSZ signal from a suite of ~ 100 reionization models using the publicly available code 21cmFAST. Our physically motivated reionization models are parameterized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of halos capable of hosting stars, and the ionizing photon mean free path. We predict the contribution of patchy reionization to be P_patchy = 1.5-3.5 micro K^2. Therefore, even when conservatively adopting a low estimate of the post-reionization signal, P_OV ~ 2 micro K^2, none of our models are consistent with the aggressive 2sigma SPT bound that does not include correlations. This implies that either: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g., very high energy X-rays or exotic particles contributed significantly; and/or (ii) that there is a significant correlation between the CIB and the tSZ. On the other hand, the conservative SPT bound is compatible with all of our models, and is on the boarder of constraining reionization.

 

 Fables of reconstruction: controlling bias in the dark energy equation of state

Authors: Robert G. Crittenden, Gong-Bo Zhao, Levon Pogosian, Lado Samushia, Xinmin Zhang

arXiv:1112.1693v1

 We develop an efficient, non-parametric Bayesian method for reconstructing the time evolution of the dark energy equation of state w(z) from observational data. Of particular importance is the choice of prior, which must be chosen carefully to minimise variance and bias in the reconstruction. Using a principal component analysis, we show how a correlated prior can be used to create a smooth reconstruction and also avoid bias in the mean behaviour of w(z). We test our method using Wiener reconstructions based on Fisher matrix projections, and also against more realistic MCMC analyses of simulated data sets for Planck and a future space-based dark energy mission. While the accuracy of our reconstruction depends on the smoothness of the assumed w(z), the relative error for typical dark energy models is <10% out to redshift z=1.5.

 

 

arXiv: 5 December 2011

Nonlinear Evolution of Cosmological Structures in Warm Dark Matter Models

Authors: Aurel Schneider, Robert E. Smith, Andrea V. Maccio, Ben Moore

arXiv:1112.0330v1

The dark energy dominated warm dark matter (WDM) model is a promising alternative cosmological scenario. We explore large-scale structure formation in this paradigm. We do this in two different ways: with the halo model approach and with the help of an ensemble of high resolution N-body simulations. Combining these quasi-independent approaches, leads to a physical understanding of the important processes which shape the formation of structures. We take a detailed look at the halo mass function, the concentrations and the linear halo bias of WDM. In all cases we find interesting deviations with respect to CDM. In particular, the concentration-mass relation displays a turnover for group scale dark matter haloes, for the case of WDM particles with masses of the order ~0.25 keV. This may be interpreted as a hint for top-down structure formation on small scales. We implement our results into the halo model and find much better agreement with simulations. On small scales the WDM halo model now performs as well as its CDM counterpart.

 

 Probing dark energy with the next generation X-ray surveys of galaxy clusters

Authors: B. Sartoris, S. Borgani, P. Rosati, J. Weller

arXiv:1112.0327v1

We present forecasts on the capability of future wide-area high-sensitivity X-ray surveys of galaxy clusters to yield constraints on the parameters defining the Dark Energy (DE) equation of state (EoS). Our analysis is carried out for future X-ray surveys which have enough sensitivity to provide accurate measurements of X-ray mass proxies and Fe-line based redshifts for about 2x10^4 clusters. We base our analysis on the Fisher Matrix formalism, by combining information on the cluster number counts and power spectrum, also including, for the first time in the analysis of the large scale cluster distribution, the effect of linear redshift-space distortions (RSDs). This study is performed with the main purpose of dissecting the cosmological information provided by geometrical and growth tests, which are both included in the analysis of number counts and clustering of galaxy clusters. We compare cosmological constraints obtained by assuming different levels of prior knowledge of the parameters which define the observable-mass X-ray relation. This comparison further demonstrates the fundamental importance of having a well calibrated observable-mass relation and, most importantly, its redshift evolution. Such a calibration can be achieved only by having at least $\sim 10^3$ net photon counts for each cluster included in the survey. We show that RSDs in the power spectrum analysis carry important cosmological information also when traced with galaxy clusters and the DE FoM increases by a factor of 8. Besides confirming the potential that large cluster surveys have in constraining the nature of DE, our analysis emphasizes that a full exploitation of the cosmological information carried by such surveys requires not only a large statistic but also a robust measurement of the mass proxies and redshifts for a significant fraction of the cluster sample, derived from the same X-ray survey data.

 

 The Dark Matter Density Profile of the Fornax Dwarf

Authors: John Jardel, Karl Gebhardt

arXiv:1112.0319v1

 We construct axisymmetric Schwarzschild models to measure the mass profile of the local group dwarf galaxy Fornax. These models require no assumptions to be made about the orbital anisotropy of the stars, as is the case for commonly used Jeans models. We test a variety of parameterizations of dark matter density profiles and find cored models with uniform density rho_c = (1.6 +/- 0.1) x 10^-2 M_sun pc^-3 fit significantly better than the cuspy halos predicted by cold dark matter simulations. We also construct models with an intermediate-mass black hole, but are unable to make a detection. We place a 1-sigma upper limit on the mass of a potential intermediate-mass black hole at M_BH < 3.2 x 10^4 M_sun.

 

 The Cosmic History of Black Hole Growth from Deep Multiwavelength Surveys

Authors: Ezequiel Treister (U. de Concepcion), C. Megan Urry (Yale)

arXiv:1112.0320v1

 Significant progress has been made in the last few years on understanding how supermassive black holes form and grow. In this paper, we begin by reviewing the spectral signatures of Active Galactic Nuclei (AGN) ranging from radio to hard X-ray wavelengths. We then describe the most commonly used methods to find these sources, including optical/UV, radio, infrared and X-ray emission and optical emission lines. We then describe the main observational properties of the obscured and unobscured AGN population. Finally, we summarize the cosmic history of black hole accretion, i.e., when in the history of the Universe supermassive black holes were getting most of their mass. We finish with a summary of open questions and a description of planned and future observatories that are going to help answer them.

 

 

arXiv: 6 December 2011

 Constraining Thawing Dark Energy using Galaxy Cluster Number Counts

Authors: N. Chandrachani Devi, T. Roy Choudhury, Anjan A. Sen

arXiv:1112.0728v1

 We study the formation of galaxy clusters in the presence of thawing class of scalar field dark energy. We consider cases where the scalar field has canonical as well non canonical kinetic term in its action. We also consider various forms for the potential of the scalar field e.g, linear, quadratic, inverse quadratic, exponential as well as Pseudo-Nambu-Goldstone Boson (PNGB) type. Moreover we investigate situation where dark energy is homogeneous as well as situation where dark energy takes part in the virialization process. We use the Sheth-Torman formalism while calculating the number density of galaxy clusters. Our results show that cluster number density for different dark energy models have significant deviation from the corresponding value for the \Lambda CDM case. The deviation is more for higher redshifts. Moreover the tachyon type scalar field with linear potential has the highest deviation from the \Lambda CDM case. For the total cluster number counts, different dark energy models can have substantial deviation from \Lambda CDM and this deviation is most significant around $z \sim 0.5 \sim 1$ for all the models we considered.

 

Lensing of 21-cm Fluctuations by Primordial Gravitational Waves

Authors: Laura Book, Marc Kamionkowski, Fabian Schmidt

arXiv:1112.0567v1

 Weak-gravitational-lensing distortions to the intensity pattern of 21-cm radiation from the dark ages can be decomposed geometrically into curl and curl-free components. Lensing by primordial gravitational waves induces a curl component, while the contribution from lensing by density fluctuations is strongly suppressed. Angular fluctuations in the 21-cm background extend to very small angular scales, and measurements at different frequencies probe different shells in redshift space. There is thus a huge trove of information with which to reconstruct the curl component of the lensing field, allowing tensor-to-scalar ratios conceivably as small as r ~ 10^{-9} - far smaller than those currently accessible - to be probed.

 

Influence of Microlensing on Spectral Anomaly of Lensed Objects

Authors: Sasa Z. Simic, Luka C. Popovic, Predrag Jovanovic

arXiv:1112.0646v1

 Here we consider the influence of the microlensing on the spectrum of a lensed object taking into account that composite emission is coming from different regions arranged subsequently around the central source. We assumed that the lensed object has three regions with the black body emission; first the innermost with the highest temperature of $10^4K$, second and third (located around the central) with slightly lower temperatures $7.5\cdot10^3$ and $5\cdot10^3$K, respectively. Than we explore the flux anomaly in lensed object due to microlensing. We compare U,V and B spectra of a such source. This results show that, due to microlensing, in a spectroscopically stratified object a flux anomaly is present.

 

 

arXiv: 29 Novemeber 2011

Cosmic microwave background constraints on the duration and timing of reionization from the South Pole Telescope

Authors: O. Zahn, C. L. Reichardt, L. Shaw, A. Lidz, K. A. Aird, B. A. Benson, L. E. Bleem, J. E. Carlstrom, C. L. Chang, H. M. Cho, T. M. Crawford, A. T. Crites, T. de Haan, M. A. Dobbs, O. Dore, J. Dudley, E. M. George, N. W. Halverson, G. P. Holder, W. L. Holzapfel, S. Hoover, Z. Hou, J. D. Hrubes, M. Joy, R. Keisler, L. Knox, A. T. Lee, E. M. Leitch, M. Lueker, D. Luong-Van, J. J. McMahon, J. Mehl, S. S. Meyer, M. Millea, J. J. Mohr, T. E. Montroy, T. Natoli, S. Padin, T. Plagge, C. Pryke, J. E. Ruhl, K. K. Schaffer, E. Shirokoff, H. G. Spieler, Z. Staniszewski, A. A. Stark, K. Story, A. van Engelen, K. Vanderlinde, J. D. Vieira, R. Williamson

arXiv:1111.6386v1

The epoch of reionization is a milestone of cosmological structure formation, marking the birth of the first objects massive enough to yield large numbers of ionizing photons. The mechanism and timescale of reionization remain largely unknown. Measurements of the CMB Doppler effect from ionizing bubbles embedded in large-scale velocity streams (the patchy kinetic Sunyaev-Zel'dovich effect) can constrain the duration of reionization. When combined with large-scale CMB polarization measurements, the evolution of the ionized fraction can be inferred. Using new multi-frequency data from the South Pole Telescope (SPT), we show that the ionized fraction evolved relatively rapidly. For our basic foreground model, we find the kinetic Sunyaev-Zel'dovich power sourced by reionization at l=3000 to be <= 2.1 micro K^2 at 95% CL. Using reionization simulations, we translate this to a limit on the duration of reionization of Delta z <= 4.4 (95% CL). We find that this constraint depends on assumptions about the angular correlation between the thermal Sunyaev-Zel'dovich power and the cosmic infrared background (CIB). Introducing the degree of correlation as a free parameter, we find that the limits on kSZ power weaken to <= 4.9 micro K^2, implying Delta z <= 7.9 (95% CL). We combine the SPT constraint on the duration of reionization with the WMAP7 measurement of the integrated optical depth to probe the cosmic ionization history. We find that reionization ended with 95% CL at z > 7.2 under the assumption of no tSZ-CIB correlation, and z>5.8 when correlations are allowed. Improved constraints from the full SPT data set in conjunction with upcoming Herschel and Planck data should detect extended reionization at >95% CL provided Delta z >= 4. (abbreviated)