Munch

We use cosmological simulations to explore the large-scale effects of reionization. Since reionization is a process that involves a large dynamic range - from galaxies to rare bright quasars - we need to be able to cover a significant volume of the universe in our simulation without losing hte important small scale effects from galaxies. Here we have taken an approach that uses clumping factors derived from small scale simulations to approximate the radiative transfer on the sub-cell scales. Using this technique, we can cover a simulation size up to $1280 h^{-1} Mpc$ with $10 h^{-1} Mpc$ cells. This allows us to construct synthetic spectra of quasars similar to observed spectra of SDSS quasars at high reshifts and compare them to the observational data. These spectra can then be analyzed for HII region sizes, the presence of the Gunn-Peterson trough and the Lyman-$\alpha$ forest.

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Cosmological Neutrinos

Is cosmology compatible with sterile neutrinos?

Authors: Scott Dodelson, Alessandro Melchiorri, Anze Slosar
Comments: 5 pages, 3 figures

By combining data from cosmic microwave background (CMB) experiments (including the recent BOOMERANG-2K2 results), large scale structure (LSS) and Lyman-$\alpha$ forest observations, we constrain the hypothesis of a fourth, sterile, massive neutrino. For the 3 massless + 1 massive neutrino case we bound the mass of the sterile neutrino to m_s<0.55eV at 95% c.l.. These results exclude at high significance the sterile neutrino hypothesis as an explanation of the LSND anomaly. We then generalize the analysis to account for active neutrino masses (which tightens the limit to m_{s}<0.51eV) and the possibility that the sterile abundance is not thermal. In the latter case, the contraints in the (mass, density) plane are non-trivial. For a mass of >1eV or <0.05eV the cosmological energy density in sterile neutrinos is always constrained to be \omega_nu<0.005 at 9% c.l.. However, for a sterile neutrino mass of ~0.25eV, omega_nu can be as large as 0.015.

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Cosmological Signatures of Interacting Neutrinos

Authors: Nicole F. Bell (Caltech), Elena Pierpaoli (Caltech), Kris Sigurdson (Caltech and IAS)
Comments: 16 pages, 14 figures, submitted to Phys. Rev. D
Report-no: KRL-MAP-309

We investigate signatures of neutrino scattering in the Cosmic Microwave Background (CMB) and matter power spectra, and the extent to which present cosmological data can distinguish between a free streaming or tightly coupled fluid of neutrinos. If neutrinos have strong non-standard interactions, for example, through the coupling of neutrinos to a light boson, they may be kept in equilibrium until late times. We show how the power spectra for these models differ from more conventional neutrino scenarios, and use CMB and large scale structure data to constrain these models. CMB polarization data improves the constraints on the number of massless neutrinos, while the Lyman-alpha power spectrum improves the limits on the neutrino mass. Neutrino mass limits depend strongly on whether some or all of the neutrino species interact and annihilate. The present data can accommodate a number of tightly-coupled relativistic degrees of freedom, and none of the interacting-neutrino scenarios considered are ruled out by current data -- although Age considerations disfavor a model with three annihilating neutrinos with very large neutrino masses.

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Production and Evolution of Perturbations of Sterile Neutrino Dark Matter

Authors: Kevork Abazajian (LANL)
Comments: submitted to Phys. Rev. D
Report-no: LA-UR 05-8831

Sterile neutrinos, fermions with no standard model couplings [SU(2) singlets], are predicted by most extensions of the standard model, and may be the dark matter. I describe the nonthermal production and linear perturbation evolution in the early universe of this dark matter candidate. I calculate production of sterile neutrino dark matter including effects of Freidmann dynamics dictated by the quark-hadron transition and particle population, the alteration of finite temperature effective mass of active neutrinos due to the presence of thermal leptons, and heating of the coupled species due to the disappearance of degrees of freedom in the plasma. These effects leave the sterile neutrinos with a non-trivial momentum distribution. I also calculate the evolution of sterile neutrino density perturbations in the early universe through the linear regime and provide a fitting function form for the transfer function describing the suppression of small scale fluctuations for this warm dark matter candidate. The results presented here differ dramatically both qualitatively and quantitatively from previous work due to the inclusion here of the relevant physical effects.

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All we know is wrong!

Recent Supernovae Ia observations tend to rule out all the cosmologies

Authors: R. G. Vishwakarma (Zacatecas University)
Comments: 10 latex pages

Dark energy and the accelerated expansion of the universe have been the direct predictions of the distant supernovae Ia observations which are also supported, indirectly, by the observations of the CMB anisotropies, gravitational lensing and the studies of galaxy clusters. Today these results are accommodated in what has become the `concordance cosmology': a universe with flat spatial sections t=constant with about 70% of its energy in the form of Einstein's cosmological constant \Lambda.
However, we find that as more and more supernovae Ia are observed, more accurately and towards higher redshift, the probability that the data are well explained by the cosmological models decreases alarmingly, finally ruling out the concordance model at more than 95% confidence level. This raises doubts against the `standard candle'-hypothesis of the supernovae Ia and their use to constrain the cosmological models.

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Detailed WMAP/X-ray comparison of 31 randomly selected nearby clusters of galaxies - incomplete Sunyaev-Zel'dovich silhouette

Authors: Richard Lieu, Jonathan P.D. Mittaz, Shuang-Nan Zhang
Comments: Correct version uploaded. 161 graphs (includes 3 WMAP filter plots and 1 ROSAT profile per cluster for 31 clusters), one large Table, ApJ submitted

The WMAP Q, V, and W band radial profiles of temperature deviation of the cosmic microwave background (CMB) were constructed for a sample of 31 randomly selected nearby clusters of galaxies in directions of Galactic latitude $|b| >$ 30$^o$. The profiles were compared in detail with the expected CMB Sunyaev-Zel'dovich effect (SZE) caused by these clusters, with the hot gas properties of each cluster obtained directly from X-ray observations, and with the WMAP point spread function fully taken into consideration. While the WMAP profiles of some clusters do exhibit the SZE, the phenomenon is also noted to be weak or absent from other clusters. A reliable overall assessment can be made using the combined (co-added) datasets of all 31 clusters, because (a) any remaining systematic uncertainties are low, and (b) the data are extremely clean (i.e. free from foreground contaminants). Both (a) and (b) are facts which we established by examining hundreds of random fields. The verdict from the 31 co-added cluster fields is that the observed SZE only accounts for about 1/4 of the expected decrement. The discrepancy represents too much extra flux for optically thin intracluster thermal emission to be the cause. Radio sources (discrete or halo) are also excluded because they have negative sloping spectra which are inconsistent with the ratio of the signals in different WMAP filters. A resolution of this discrepancy between predicted and observed decrements have potentially extreme ramifications for our interpretation of the CMB. One is forced to conclude that either the CMB is non-cosmological, or there are issues with the WMAP data itself which must be taken into account when interpreting the CMB emission.

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Apparent Hubble acceleration from large-scale electroweak domain structure

Authors: Tommy Anderberg
Comments: 11 pages, 7 figures

The observed luminosity deficit of Type Ia supernovae (SNe Ia) at high redshift z can be explained by partial conversion to weak vector bosons of photons crossing large-scale electroweak domain boundaries, making Hubble acceleration only apparent and eliminating the need for a cosmological constant > 0.

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Producing a Scale-Invariant Spectrum of Perturbations in a Hagedorn Phase of String Cosmology

Authors: Ali Nayeri, Robert H. Brandenberger, Cumrun Vafa
Comments: 4 pages, 1 figure
Report-no: HUTP-05/A048

We study the generation of cosmological perturbations during the Hagedorn phase of string gas cosmology. Using tools of string thermodynamics we provide indications that it may be possible to obtain a nearly scale-invariant spectrum of cosmological fluctuations on scales which are of cosmological interest today. In our cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period of cosmological inflation.

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Measurement of the Spatial Cross-Correlation Function of Damped Lyman Alpha Systems and Lyman Break Galaxies

Authors: J. Cooke (1), A. M. Wolfe (1), E. Gawiser (2), J. X. Prochaska (3), ((1) UC San Diego, (2) Yale University, (3) UC Santa Cruz/UCO-Lick Observatory)
Comments: 12 pages, 2 figures, accepted for publication in Astrophysical Journal Letters

We present the first spectroscopic measurement of the spatial cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with 11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5 photometrically selected z > 2 LBGs. We find strong evidence for an overdensity of LBGs near DLAs versus random, the results of which are similar to that of LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a fixed value of gamma = 1.6. The implications of the DLA-LBG clustering amplitude on the average dark matter halo mass of DLAs are discussed.

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Can Inflation solve the Hierarchy Problem?

Authors: Tirthabir Biswas, Alessio Notari
Comments: 7 pages

Inflation with tunneling from a false to a true vacuum becomes viable in the presence of a scalar field that slows down the initial de Sitter phase. As a by-product this field also sets dynamically the value of the Newton constant observed today. This can be very large if the tunneling rate (which is exponentially sensitive to the barrier) is small enough. Therefore along with Inflation we also provide a natural dynamical explanation for why gravity is so weak today. Moreover we predict a spectrum of gravity waves peaked at around 0.1 mHz, that will be detectable by the planned space inteferometer LISA.

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