A circular polarimeter for the Cosmic Microwave Background

Abstract

A primordial degree of circular polarization of the Cosmic Microwave Background is not observationally excluded. The hypothesis of primordial dichroism can be quantitatively falsified if the plasma is magnetized prior to photon decoupling since the initial V-mode polarization affects the evolution of the temperature fluctuations as well as the equations for the linear polarization. The observed values of the temperature and polarization angular power spectra are used to infer constraints on the amplitude and on the spectral slope of the primordial V-mode. Prior to photon decoupling magnetic fields play the role of polarimeters insofar as they unveil the circular dichroism by coupling the V-mode power spectrum to the remaining brightness perturbations. Conversely, for angular scales ranging between 4 deg and 10 deg the joined bounds on the magnitude of circular polarization and on the magnetic field intensity suggest that direct limits on the V-mode power spectrum in the range of 0.01 mK could directly rule out pre-decoupling magnetic fields in the range of 10-100 nG. The frequency dependence of the signal is located, for the present purposes, in the GHz range.

28 pages, 12 included figures.

References in corpus (8)

• Improved measurements of the temperature and polarization of the CMB from QUaD
• Generation of circular polarization of the CMB
• Faraday rotation, stochastic magnetic fields and CMB maps
• TRIS II: search for CMB spectral distortions at 0.60, 0.82 and 2.5 GHz
• TRIS III: the diffuse galactic radio emission at $\delta =+42^{\circ }$
• The V-mode polarization of the Cosmic Microwave Background
• Characterization of the Millimeter-Wave Polarization of Centaurus A with QUaD
• Circular dichroism, magnetic knots and the spectropolarimetry of the Cosmic Microwave Background

Cited by in corpus (5)

• Axion Dark Matter Detection with CMB Polarization
• An improved upper limit to the CMB circular polarization at large angular scales
• Probing large-scale magnetism with the Cosmic Microwave Background
• On the CMB circular polarization. I. The Cotton-Mouton effect
• Magnetic field contribution to the last electron-photon scattering