CMB Anomalies from Relic Anisotropy

Most of the analysis of the Cosmic Microwave Background relies on the assumption of statistical isotropy. However, given some recent evidence pointing against isotropy, as for instance the observed alignment of different multipoles on large scales, it is worth testing this assumption against the increasing amount of available data. As a pivot model, we assume that the spectrum of the primordial perturbations depends also on their directionality (rather than just on the magnitude of their momentum, as in the standard case). We explicitly compute the correlation matrix for the temperature anisotropies in the simpler case in which there is a residual isotropy between two spatial directions. As a concrete example, we consider a different initial expansion rate along one direction, and the following isotropization which takes place during inflation. Depending on the amount of inflation, this can lead to broken statistical isotropy on the largest observable scales.Comment: 6 pages, 2 .ps figure

Generating non-Gaussian maps with a given power spectrum and bispectrum

We propose two methods for generating non-Gaussian maps with fixed power spectrum and bispectrum. The first makes use of a recently proposed rigorous, non-perturbative, Bayesian framework for generating non-Gaussian distributions. The second uses a simple superposition of Gaussian distributions. The former is best suited for generating mildly non-Gaussian maps, and we discuss in detail the limitations of this method. The latter is better suited for the opposite situation, i.e. generating strongly non-Gaussian maps. The ensembles produced are isotropic and the power spectrum can be jointly fixed; however we cannot set to zero all other higher order cumulants (an unavoidable mathematical obstruction). We briefly quantify the leakage into higher order moments present in our method. We finally present an implementation of our code within the HEALPIX packageComment: 22 pages submitted to PRD, astro-ph version only includes low resolution map

Polarization Diffusion from Spacetime Uncertainty

A model of Lorentz invariant random fluctuations in photon polarization is presented. The effects are frequency dependent and affect the polarization of photons as they propagate through space. We test for this effect by confronting the model with the latest measurements of polarization of Cosmic Microwave Background (CMB) photons.Comment: 4 pages, 1 figur

Cosmic microwave background snapshots: pre-WMAP and post-WMAP

Abbreviated: We highlight the remarkable evolution in the CMB power spectrum over the past few years, and in the cosmological parameters for minimal inflation models derived from it. Grand unified spectra (GUS) show pre-WMAP optimal bandpowers are in good agreement with each other and with the one-year WMAP results, which now dominate the L < 600 bands. GUS are used to determine calibrations, peak/dip locations and heights, and damping parameters. These CMB experiments significantly increased the case for accelerated expansion in the early universe (the inflationary paradigm) and at the current epoch (dark energy dominance) when they were combined with `prior' probabilities on the parameters. A minimal inflation parameter set is applied in the same way to the evolving data. Grid-based and and Monte Carlo Markov Chain methods are shown to give similar values, highly stable over time and for different prior choices, with the increasing precision best characterized by decreasing errors on uncorrelated parameter eigenmodes. After marginalizing over the other cosmic and experimental variables for a weak+LSS prior, the pre-WMAP data of Jan03 cf. the post-WMAP data of Mar03 give Omega_{tot} =1.03^{+0.05}_{-0.04} cf. 1.02^{+0.04}_{-0.03}. Adding the flat prior, n_s =0.95^{+0.07}_{-0.04} cf. 0.97^{+0.02}_{-0.02}, with < 2\sigma evidence for a log variation of n_s. The densities have concordance values. The dark energy pressure-to-density ratio is not well constrained by our weak+LSS prior, but adding SN1 gives w_Q < -0.7. We find \sigma_8 = 0.89^{+0.06}_{-0.07} cf. 0.86^{+0.04}_{-0.04}, implying a sizable SZ effect; the high L power suggest \sigma_8 \sim 0.94^{+0.08}_{-0.16} is needed to be SZ-compatible.Comment: 36 pages, 5 figures, 5 tables, Jan 2003 Roy Soc Discussion Meeting on `The search for dark matter and dark energy in the Universe', published PDF (Oct 15 2003) is http://www.cita.utoronto.ca/~bond/roysoc03/03TA2435.pd

On the evolution of tachyonic perturbations at super-Hubble scales

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a non-canonical scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations can be enhanced or suppressed at super-Hubble scales if there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations during the fast roll regime proves to be responsible for the change in the amplitude of the curvature perturbations at super-Hubble scales. Furthermore, following the earlier analysis for the canonical scalar field, we show that the power spectrum evaluated in the long wavelength approximation matches the exact power spectrum obtained numerically very well. Finally, we briefly comment on an application of this phenomenon.Comment: v1: 15 pages, 4 figures; v2: 16 pages, 5 figures, power spectrum included, discussion in section 5 enlarged, references added; v3: 17 pages, 5 figures, enhancement AS WELL AS suppression of modes at super-Hubble scales pointed out, title changed, discussions enlarged, references added, to appear in JCA

Chaplygin gas with non-adiabatic pressure perturbations

Perturbations in a Chaplygin gas, characterized by an equation of state $p = -A/\rho$, may acquire non-adiabatic contributions if spatial variations of the parameter $A$ are admitted. This feature is shown to be related to a specific internal structure of the Chaplygin gas. We investigate how perturbations of this type modify the adiabatic sound speed and influence the time dependence of the gravitational potential which gives rise to the Integrated Sachs-Wolfe effect in the anisotropy spectrum of the cosmic microwave background.Comment: 16 pages, comments and references added, accepted for publication in Class.Quantum Gra

Gravity Waves Signatures from Anisotropic pre-Inflation

We show that expanding or contracting Kasner universes are unstable due to the amplification of gravitational waves (GW). As an application of this general relativity effect, we consider a pre-inflationary anisotropic geometry characterized by a Kasner-like expansion, which is driven dynamically towards inflation by a scalar field. We investigate the evolution of linear metric fluctuations around this background, and calculate the amplification of the long-wavelength GW of a certain polarization during the anisotropic expansion (this effect is absent for another GW polarization, and for scalar fluctuations). These GW are superimposed to the usual tensor modes of quantum origin from inflation, and are potentially observable if the total number of inflationary e-folds exceeds the minimum required to homogenize the observable universe only by a small margin. Their contribution to the temperature anisotropy angular power spectrum decreases with the multipole l as l^(-p), where p depends on the slope of the initial GW power-spectrum. Constraints on the long-wavelength GW can be translated into limits on the total duration of inflation and the initial GW amplitude. The instability of classical GW (and zero-vacuum fluctuations of gravitons) during Kasner-like expansion (or contraction) may have other interesting applications. In particular, if GW become non-linear, they can significantly alter the geometry before the onset of inflation

Curvature-induced phase transitions in the inflationary universe - Supersymmetric Nambu-Jona-Lasinio Model in de Sitter spacetime -

The phase structure associated with the chiral symmetry is thoroughly investigated in de Sitter spacetime in the supersymmetric Nambu-Jona-Lasinio model with supersymmetry breaking terms. The argument is given in the three and four space-time dimensions in the leading order of the 1/N expansion and it is shown that the phase characteristics of the chiral symmetry is determined by the curvature of de Sitter spacetime. It is found that the symmetry breaking takes place as the first order as well as second order phase transition depending on the choice of the coupling constant and the parameter associated with the supersymmetry breaking term. The critical curves expressing the phase boundary are obtained. We also discuss the model in the context of the chaotic inflation scenario where topological defects (cosmic strings) develop during the inflation.Comment: 29 pages, 6 figures, REVTe

Instrumental and Analytic Methods for Bolometric Polarimetry

We discuss instrumental and analytic methods that have been developed for the first generation of bolometric cosmic microwave background (CMB) polarimeters. The design, characterization, and analysis of data obtained using Polarization Sensitive Bolometers (PSBs) are described in detail. This is followed by a brief study of the effect of various polarization modulation techniques on the recovery of sky polarization from scanning polarimeter data. Having been successfully implemented on the sub-orbital Boomerang experiment, PSBs are currently operational in two terrestrial CMB polarization experiments (QUaD and the Robinson Telescope). We investigate two approaches to the analysis of data from these experiments, using realistic simulations of time ordered data to illustrate the impact of instrumental effects on the fidelity of the recovered polarization signal. We find that the analysis of difference time streams takes full advantage of the high degree of common mode rejection afforded by the PSB design. In addition to the observational efforts currently underway, this discussion is directly applicable to the PSBs that constitute the polarized capability of the Planck HFI instrument.Comment: 23 pages, 11 figures. for submission to A&