Pseudoscalar perturbations and polarization of the cosmic microwave background

TL;DR

This paper demonstrates that pseudoscalar fields coupled to photons during inflation can significantly convert E-mode polarization to B-mode in the CMB, allowing constraints on new physics models with high sensitivity.

Contribution

It introduces a novel method to probe massless pseudoscalar fields via CMB polarization anisotropies, surpassing previous experimental sensitivities.

Findings

Current B-mode limits constrain the pseudoscalar-photon coupling ratio to less than 0.07.

This method can probe pseudoscalar decay constants f_a exceeding 10^{14} GeV.

The approach offers a new window into physics beyond the Standard Model during inflation.

Abstract

We show that models of new particle physics containing massless pseudoscalar fields super-weakly coupled to photons can be very efficiently probed with CMB polarization anisotropies. The stochastic pseudoscalar fluctuations generated during inflation provide a mechanism for converting E-mode polarization to B-mode during photon propagation from the surface of last scattering. The efficiency of this conversion process is controlled by the dimensionless ratio H/(2\pi f_a), where H is the Hubble scale during inflation, and f_a^{-1} is the strength of the pseudoscalar coupling to photons. The current observational limits on the B-mode constrain this ratio to be less than 0.07, which in many models of inflation translates to a sensitivity to values of f_a in excess of 10^{14} GeV, surpassing the sensitivity of other tests.