Detection ofB-Mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope

Abstract

Gravitational lensing of the cosmic microwave background generates a curl pattern in the observed polarization. This "B-mode" signal provides a measure of the projected mass distribution over the entire observable Universe and also acts as a contaminant for the measurement of primordial gravitywave signals. In this Letter we present the first detection of gravitational lensing B modes, using first-season data from the polarization-sensitive receiver on the South Pole Telescope (SPTpol). We construct a template for the lensing B-mode signal by combining E-mode polarization measured by SPTpol with estimates of the lensing potential from a Herschel -SPIRE map of the cosmic infrared background. We compare this template to the B modes measured directly by SPTpol, finding a non-zero correlation at 7.7σ significance. The correlation has an amplitude and scale-dependence consistent with theoretical expectations, is robust with respect to analysis choices, and constitutes the first measurement of a powerful cosmological observable. [2,3]. B modes are not generated at linear order in perturbation theory by the scalar perturbations which are the dominant source of CMB temperature and E-mode anisotropies. Because of this, B modes are of great interest as a clean probe of two more subtle signals: (1) primordial tensor perturbations in the early Universe [4,5], the measurement of which would provide a unique probe of the energy scale of inflation; and (2) gravitational lensing, which generates a distinctive nonGaussian B-mode signal [6] that can be used to measure the projected mass distribution and constrain cosmological parameters such as the sum of neutrino masses (for a review, see [7]).Previous experiments have placed upper limits on the B-mode polarization anisotropy [8][9][10][11]. In this Letter we present the first detection of B modes sourced by gravitational lensing, using first-season data from SPTpol, the polarization-sensitive receiver on the South Pole Telescope.Gravitational lensing remaps the observed position of CMB anisotropies asn →n+∇φ(n), where φ is the CMB lensing potential [12]. This remapping mixes some of the (relatively) large E-mode signal into B. The induced B mode at Fourier wavevector l B is given to first order in φ as [13]

Status of Neutrino Properties and Future Prospects—Cosmological and Astrophysical Constraints

“…An alternative reconstruction technique is based on the possibility to crosscorrelate the CMB signal with tracers of large-scale structures, 6 We are assuming that the lensing field is isotropic. such as Cosmic Infrared Background (CIB) maps, therefore leading to an "external" reconstruction [56] (opposite to the "internal" reconstruction performed with the use of CMB-based only estimators [57,58]). …”

Neutrino Physics from the Cosmic Microwave Background and Large-Scale Structure

“…Polarization surveys will represent a large improvement over what can be done with temperature. Gravitational lensing of primordial E modes by intervening matter distributions produces a B-mode polarization signal [36], which has recently been detected [11]. This lensing-induced B-mode polarization corresponds to an RMS of ∼ 5 µK-arcmin with a characteristic angular scale is a few arcminutes.…”

“…Significant progress has been made recently in these areas, with the first projected mass reconstructions from CMB lensing [5,6,7,8,9,10], detection of the CMB lensing B-mode polarization [11], and percent level measurements of the distance scale from BAO measurements [12,13,14,15].…”

Polarization and Polarimetry: A Review

“…More recently, the Planck satellite has begun a polarization monitoring program aimed at both E and B modes (see, e.g., Lamarre et al 2003 for technical details), and an observation of B mode polarization by a ground-based CMB telescope has been reported (Hanson et al 2013). …”