B-modes from Post-inflationary Gravitational Waves Sourced by Axionic Instabilities at Cosmic Reionization

TL;DR

This paper proposes a mechanism where axion-like particles induce gravitational waves during reionization, leading to observable B-mode polarization signals in the CMB, potentially detectable by future experiments.

Contribution

It introduces a novel source of B-mode polarization from axion-induced dark photon instabilities during reionization, linking particle physics to observable cosmological signals.

Findings

Dark photon instabilities generate gravitational waves at reionization.

These waves produce B-mode polarization detectable by future CMB experiments.

Parameter ranges are consistent with current experimental constraints.

Abstract

We show that axion-like particles that only couple to invisible dark photons can generate visible B-mode signals around the reionization epoch. The axion field starts rolling shortly before reionization, resulting in a tachyonic instability for the dark photons. This generates an exponential growth of the dark photon quanta sourcing both scalar metric modes and gravitational waves that leave an imprint on the reionized baryons. The tensor modes modify the cosmic microwave background (CMB) polarization at reionization, generating visible B-mode signatures for the next generation of CMB experiments for parameter ranges that satisfy the current experimental constraints.