Munch

Authors: Thomas Flacke, Dan Hooper, John March-Russell
Categories: hep-ph
Comments: 15 pages, 3 figures
Report-no: OUTP-04/25P; FERMILAB-PUB-05-416-A

We study constraints on models with a flat "Universal'' Extra Dimension in which all Standard Model fields propagate in the bulk. A significantly improved constraint on the compactification scale is obtained from the extended set of electroweak precision observables accurately measured at LEP1 and LEP2. We find a lower bound of M_c = R^{-1} > 700 (800) GeV at the 99% (95%) confidence level. We also discuss the implications of this constraint on the prospects for the direct and indirect detection of Kaluza-Klein dark matter in this model.

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Testing Primordial Non-Gaussianity in CMB Anisotropies

Authors: M. Liguori, F. K. Hansen, E. Komatsu, S. Matarrese, A. Riotto
Categories: astro-ph
Comments: 25 pages, 3 figures, 1 table, submitted to Phys. Rev. D
Report-no: FERMILAB-PUB-05-386-T

Recent second-order perturbation computations have provided an accurate prediction for the primordial gravitational potential $\Phi(x)$ in scenarios in which cosmological perturbations are generated either during or after inflation. This enables us to make realistic predictions for a non-Gaussian part of $\Phi(x)$, which is generically written in momentum space as a double convolution of its Gaussian part with a suitable kernel, f_NL(k1,k2). This kernel defines the amplitude and angular structure of the non-Gaussian signals and originates from the evolution of second-order perturbations after the generation of the curvature perturbation. We derive a generic formula for the CMB angular bispectrum with arbitrary f_NL(k1,k2) and examine the detectability of the primordial non-Gaussian signals from various scenarios such as single-field inflation, inhomogeneous reheating, and curvaton scenarios. Our results show that in the standard slow-roll inflation scenario the signal actually comes from the momentum-dependent part of f_NL(k1,k2), and thus it is important to include the momentum dependence in the data analysis. In the other scenarios the primordial non-Gaussianity is comparable to or larger than these post-inflationary effects. We find that WMAP cannot detect non-Gaussian signals generated by these models. Numerical calculations for l>500 are still computationally expensive, and we are not yet able to extend our calculations to Planck's angular resolution; however, there is an encouraging trend which shows that Planck may be able to detect these non-Gaussian signals.

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Limits on non-Gaussianities from WMAP data

Authors: Paolo Creminelli, Alberto Nicolis, Leonardo Senatore, Max Tegmark, Matias Zaldarriaga
Categories: astro-ph hep-ph hep-th
Comments: 20 pages, 12 eps figures
Report-no: HUTP-05/A0038, MIT-CTP 3670

We develop a method to constrain the level of non-Gaussianity of density perturbations when the 3-point function is of the "equilateral" type. Departures from Gaussianity of this form are produced by single field models such as ghost or DBI inflation and in general by the presence of higher order derivative operators in the effective Lagrangian of the inflaton. We show that the induced shape of the 3-point function can be very well approximated by a factorizable form, making the analysis practical. We also show that, unless one has a full sky map with uniform noise, in order to saturate the Cramer-Rao bound for the error on the amplitude of the 3-point function, the estimator must contain a piece that is linear in the data. We apply our technique to the WMAP data obtaining a constraint on the amplitude f_NL^equil of "equilateral" non-Gaussianity: -366 < f_NL^equil < 238 at 95% C.L. We also apply our technique to constrain the so-called "local" shape, which is predicted for example by the curvaton and variable decay width models. We show that the inclusion of the linear piece in the estimator improves the constraint over those obtained by the WMAP team, to -27 < f_NL^local < 121 at 95% C.L.

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Can the Acceleration of Our Universe Be Explained by the Effects of Inhomogeneities?

Authors: Akihiro Ishibashi, Robert M. Wald
Categories: gr-qc astro-ph hep-th
Comments: 19 pages, 1 figure

No. It is simply not plausible that cosmic acceleration could arise within the context of general relativity from a back-reaction effect of inhomogeneities in our universe, without the presence of a cosmological constant or ``dark energy.'' We point out that our universe appears to be described very accurately on all scales by a Newtonianly perturbed FLRW metric. (This assertion is entirely consistent with the fact that we commonly encounter $\delta \rho/\rho > 10^{30}$.) If the universe is accurately described by a Newtonianly perturbed FLRW metric, then the back-reaction of inhomogeneities on the dynamics of the universe is negligible. If not, then it is the burden of an alternative model to account for the observed properties of our universe. We emphasize with concrete examples that it is {\it not} adequate to attempt to justify a model by merely showing that some spatially averaged quantities behave the same way as in FLRW models with acceleration. A quantity representing the ``scale factor'' may ``accelerate'' without there being any physically observable consequences of this acceleration. It also is {\it not} adequate to calculate the second-order stress energy tensor and show that it has a form similar to that of a cosmological constant of the appropriate magnitude. The second-order stress energy tensor is gauge dependent, and if it were large, contributions of higher perturbative order could not be neglected. We attempt to clear up the apparent confusion between the second-order stress energy tensor arising in perturbation theory and the ``effective stress energy tensor'' arising in the ``shortwave approximation.''

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Point Source Confusion in SZ Cluster Surveys

Authors: James G. Bartlett (APC-Univ. Paris 7), Jean-Baptiste Melin (Univ. California, Davis)
Categories: astro-ph
Comments: Accepted for publication in Astronomy & Astrophysics

We examine the effect of point source confusion on cluster detection in Sunyaev-Zel'dovich (SZ) surveys. A filter matched to the spatial and spectral characteristics of the SZ signal optimally extracts clusters from the astrophysical backgrounds. We calculate the expected confusion (point source and primary cosmic microwave background [CMB]) noise through this filter and quantify its effect on the detection threshold for both single and multiple frequency surveys. Extrapolating current radio counts, we estimate that confusion from sources below 100 microJy limits single-frequency surveys to 1-sigma detection thresholds of Y 3.10^{-6} arcmin^2 at 30 GHz and Y 10^{-5} arcmin^2 at 15 GHz (for unresolved clusters in a 2 arcmin beam); these numbers are highly uncertain, and an extrapolation with flatter counts leads to much lower confusion limits. Bolometer surveys must contend with an important population of infrared point sources. We find that a three-band matched filter with 1 arcminute resolution (in each band) efficiently reduces confusion, but does not eliminate it: residual point source and CMB fluctuations contribute significantly the total filter noise. In this light, we find that a 3-band filter with a low-frequency channel (e.g, 90+150+220 GHz) extracts clusters more effectively than one with a high frequency channel (e.g, 150+220+300 GHz).

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Statistics of Physical Properties of Dark Matter Clusters

Authors: L. Shaw, J. Weller, J.P. Ostriker, P. Bode
Categories: astro-ph
Comments: Submitted to ApJ, higher resolution version available at this http URL

We have identified over 2000 well resolved cluster halos, and also their associated bound subhalos, from the output of 1024^3 particle cosmological N-body simulation (of box size 320h^{-1}Mpc and softening length 3.2h^{-1}kpc). We present an algorithm to identify those halos still in the process of relaxing into dynamical equilibrium, and a detailed analysis of the integral and internal physical properties for all the halos in our sample. The majority are prolate, and tend to rotate around their minor principle axis. We find there to be no correlation between the spin and virial mass of the clusters halos and that the higher mass halos are less dynamically relaxed and have a lower concentration. Additionally, the orbital angular momentum of the substructure is typically well aligned with the rotational angular momentum of the `host' halo. There is also evidence of the transfer of angular momentum from subhalos to their host. Overall, we find that measured halo properties are often significantly influenced by the fraction of mass contained within substructure. Dimensionless properties do depend weakly on the ratio of halo mass (M_h) to our characteristic mass scale (M_* = 8x10^{14}h^{-1}M_sun). This lack of self-similarity is in the expected sense in that, for example, 'old halos' with M_h / M_* << 1 have less substructure than 'young halos' with M_h / M_* >> 1.

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Probing Reionization with the Cosmological Proximity Effect and High-Redshift Supernovae Rates

Authors: Andrei Mesinger
Categories: astro-ph
Comments: 10 pages, 2 figures; to appear in the proceedings of UC Irvine May 2005 workshop on "First Light & Reionization", eds. E. Barton & A. Cooray, New Astronomy Reviews, in press

We develop and assess the potential of several powerful techniques, designed to investigate the details of reionization. First, we present a procedure to probe the neutral fraction, x_HI, using the Lyman alpha transmission statistics of high-redshift (z > 6) sources. We find that only tens of bright quasar spectra could distinguish between x_HI ~ 1 and x_HI < 0.01. A rudimentary application of such a technique on quasar SDSS J1030+0524 has yielded compelling evidence of a large neutral fraction (x_HI > 0.2) at z ~ 6. We also generate the observable, high-z supernovae (SNe) rates and quantify the prospects of detecting the suppression of star-formation in low-mass galaxies at reionization from such SNe rates, specifically from those obtainable from the James Webb Space Telescope (JWST). Our analysis suggests that searches for SNe could yield thousands of SNe per unit redshift at z ~ 6, and be a valuable tool at studying reionization features and feedback effects out to z < 13.

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Imprint of Inhomogeneous Reionization on the Power Spectrum of Galaxy Surveys at High Redshifts

Authors: Daniel Babich, Abraham Loeb (Harvard University)
Categories: astro-ph
Comments: 8 pages, 5 figures, submitted to ApJ

We consider the effects of inhomogeneous reionization on the distribution of galaxies at high redshifts. Modulation of the formation process of the ionizing sources by large scale density modes makes reionization inhomogeneous and introduces a spread to the reionization times of different regions with the same size. After sources photo-ionize and heat these regions to a temperature $\ga 10^4$K at different times, their temperatures evolve as the ionized intergalactic medium (IGM) expands. The varying IGM temperature makes the minimum mass of galaxies spatially non-uniform with a fluctuation amplitude that increases towards small scales. These scale-dependent fluctuations modify the shape of the power spectrum of low-mass galaxies at high redshifts in a way that depends on the history of reionization. The resulting distortion of the primordial power spectrum is significantly larger than changes associated with uncertainties in the inflationary parameters, such as the spectral index of the scalar power spectrum or the running of the spectral index. Future surveys of high-redshift galaxies will offer a new probe of the thermal history of the IGM but might have a more limited scope in constraining inflation.

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A universal density slope - velocity anisotropy relation

Authors: Steen H. Hansen, Ben Moore, Joachim Stadel
Categories: astro-ph
Comments: 4 pages, 1 figure, to appear in the XXIst IAP Colloquium "Mass Profiles and Shapes of Cosmological Structures", Paris 4-9 July 2005, France, (Eds.) G. Mamon, F. Combes, C. Deffayet, B. Fort, EAS Publications Series

One can solve the Jeans equation analytically for equilibrated dark matter structures, once given two pieces of input from numerical simulations. These inputs are 1) a connection between phase-space density and radius, and 2) a connection between velocity anisotropy and density slope, the \alpha-\beta relation. The first (phase-space density v.s. radius) has been analysed through several different simulations, however the second (\alpha-\beta relation) has not been quantified yet. We perform a large set of numerical experiments in order to quantify the slope and zero-point of the \alpha-\beta relation. When combined with the assumption of phase-space being a power-law in radius this allows us to conclude that equilibrated dark matter structures indeed have zero central velocity anisotropy, central density slope of \alpha_0 = -0.8, and outer anisotropy of approximately \beta_\infinity = 0.5.

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The Dependence of Clustering on Galaxy Properties

Authors: Cheng Li, Guinevere Kauffmann, Y.P. Jing, Simon D.M. White, Gerhard Boerner, F.Z. Cheng
Categories: astro-ph
Comments: 18 pages, 14 figures, submitted to Monthly Notices, Tables 5 and 6 will be available in electronic form

(abridged)We use a sample of ~200,000 galaxies drawn from the Sloan Digital Sky Survey to study how clustering depends on properties such as stellar mass (M*), colour (g-r), 4000A break strength (D4000), concentration index (C), and stellar surface mass density (\mu_*). We find that more massive galaxies cluster more strongly than less massive galaxies, with the difference increasing above the characteristic stellar mass of the Schechter mass function. When divided by physical quantities, galaxies with redder colours, larger D4000, higher C and larger \mu_* cluster more strongly. The clustering differences are largest on small scales and for low mass galaxies. At fixed stellar mass,the dependences of clustering on colour and 4000A break strength are similar. Different results are obtained when galaxies are split by concentration or surface density. The dependence of w(r_p) on g-r and D4000 extends out to physical scales that are significantly larger than those of individual dark matter haloes (> 5 Mpc/h). This large-scale clustering dependence is not seen for the parameters C or \mu_*. On small scales (< 1 Mpc/h), the amplitude of the correlation function is constant for ``young'' galaxies with 1.1 < D4000< 1.5 and a steeply rising function of age for ``older'' galaxies with D4000>1.5. In contrast, the dependence of the amplitude of w(r_p) on concentration on scales less than 1 Mpc/h is strongest for disk-dominated galaxies with C<2.6. This demonstrates that different processes are required to explain environmental trends in the structure and in star formation history of galaxies.

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Cluster Merger Variance and the Luminosity Gap Statistic

Authors: Milos Milosavljevic (Caltech), Christopher J. Miller (CTIO), Steven R. Furlanetto (Caltech), Asantha Cooray (UC Irvine)
Categories: astro-ph
Comments: 5 pages, 3 figures

The presence of multiple luminous galaxies in clusters can be explained by the finite time over which a galaxy sinks to the center of the cluster and merges with the the central galaxy. The simplest measurable statistic to quantify the dynamical age of a system of galaxies is the luminosity (magnitude) gap, which is the difference in photometric magnitude between the two most luminous galaxies. We present a simple analytical estimate of the luminosity gap distribution in groups and clusters as a function of dark matter halo mass. The luminosity gap is used to define "fossil" groups; we expect the fraction of fossil systems to exhibit a strong and model-independent trend with mass: ~1-3% of massive clusters and ~5-40% of groups should be fossil systems. We also show that, on cluster scales, the observed intrinsic scatter in the central galaxy luminosity-halo mass relation can be ascribed to dispersion in the merger histories of satellites within the cluster. We compare our predictions to the luminosity gap distribution in a sample of 730 clusters in the Sloan Digital Sky Survey C4 Catalog and find good agreement. This suggests that theoretical excursion set merger probabilities and the standard theory of dynamical segregation are valid on cluster scales.

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