The Cosmic Microwave Background Quadrupole in a Polarized Light

Olivier Dore,Abraham Loeb,Gilbert P Holder

doi:10.1086/422496

Abstract

The low quadrupole of the cosmic microwave background (CMB), measured by the Cosmic Background Explorer (COBE) and confirmed by the Wilkinson Microwave Anisotropy Probe (WMAP), has generated much discussion recently. We point out that the well-known correlation between temperature and polarization anisotropies of the CMB further constrains the low-multipole anisotropy data. This correlation originates from the fact that the low-multipole polarization signal is sourced by the CMB quadrupole as seen by free electrons during the relatively recent cosmic history. Consequently, the large-angle temperature anisotropy data make restrictive predictions for the large-angle polarization anisotropy, which depend primarily on the optical depth for electron scattering after cosmological recombination, τ. We show that if current cosmological models for the generation of large-angle anisotropy are correct and the COBE/WMAP data are not significantly contaminated by non-CMB signals, then the observed C amplitude on the largest scales is discrepant at the ~99.8% level with the observed C for the concordant ΛCDM model with τ = 0.10. Using τ = 0.17, the preferred WMAP model-independent value, the discrepancy is at the level of 98.5%.

Highlights

The low quadrupole of the cosmic microwave background (CMB), measured by the Cosmic Background Explorer (COBE; Bennett et al 1996) and confirmed by the Wilkinson Microwave Anisotropy Probe (WMAP; Bennett et al 2003), has generated much discussion recently, with several papers offering various possible causes for suppressed power on very large scales (e.g., Bond 1995; Efstathiou 2003a; Bridle et al 2003; Contaldi et al 2003; Tegmark et al 2003; Cline et al 2003; Feng & Zhang 2003)
We show that if current cosmological models for the generation of large-angle anisotropy are correct and the COBE/WMAP data are not significantly contaminated by non-CMB signals, the observed ClTE amplitude on the largest scales is discrepant at the $99.8% level with the observed ClTT for the concordant ÃCDM model with 1⁄4 0:10
Most of the large-scale polarized signals we consider here originated from Thomson scattering of the CMB quadrupole at the relatively recent epoch following the reionization of the universe (Zaldarriaga 1997)

Summary

INTRODUCTION

The low quadrupole (and first few multipoles) of the cosmic microwave background (CMB), measured by the Cosmic Background Explorer (COBE; Bennett et al 1996) and confirmed by the Wilkinson Microwave Anisotropy Probe (WMAP; Bennett et al 2003), has generated much discussion recently, with several papers offering various possible causes for suppressed power on very large scales (e.g., Bond 1995; Efstathiou 2003a; Bridle et al 2003; Contaldi et al 2003; Tegmark et al 2003; Cline et al 2003; Feng & Zhang 2003). The correlation between temperature and polarization anisotropies is well known (Zaldarriaga & Seljak 1997) It has been detected by Leitch et al (2002) on intermediate angular scales and measured by the WMAP experiment on the scales of interest here ( Kogut et al 2003). For a given realization of the CMB sky, the measured temperature anisotropy power at a given multipole, ClTT , will have some amount of intrinsic scatter, as will the polarization anisotropy power, ClEE, and the cross power spectrum, ClTE. These measures of the power are correlated. We present results of consistency tests using current data and estimate the range of possible future data that could be comfortably accommodated within the currently accepted cosmological models

TT-TE CORRELATIONS

MONTE CARLO METHODOLOGY

MONTE CARLO RESULTS

COSMOLOGICAL IMPLICATIONS

CONCLUSIONS