Effective Theory of Inflationary Magnetogenesis and Constraints on Reheating

TL;DR

This paper develops an effective theory framework for primordial magnetogenesis, analyzing electromagnetic field evolution during reheating, and constrains reheating parameters using observational data and physical effects like Faraday induction.

Contribution

It introduces a general effective theory approach to inflationary magnetogenesis, including parity violation and reheating effects, providing new constraints on reheating parameters.

Findings

Reheating phase significantly influences magnetic field strength.

Faraday induction enhances present-day magnetic fields.

Reheating equation of state is tightly constrained to 0.01 < ω_eff < 0.27.

Abstract

Effective theory framework based on symmetry has recently gained widespread interest in the field of cosmology. In this paper, we apply the same idea on the genesis of the primordial magnetic field and its evolution throughout the cosmological universe. Given the broken time-diffeomorphism symmetry by the cosmological background, we considered the most general Lagrangian of electromagnetic and metric fluctuation up to second order, which naturally breaks conformal symmetry in the electromagnetic (EM) sector. We also include parity violation in the electromagnetic sector with the motivation that has potential observational significance. In such a set-up, we explore the evolution of EM, scalar, and tensor perturbations considering different observational constraints. In our analysis we emphasize the role played by the intermediate reheating phase which has got limited interest in all the previous studies. Assuming the vanishing electrical conductivity during the entire period of reheating, the well-known Faraday electromagnetic induction has been shown to play a crucial role in enhancing the strength of the present-day magnetic field. We show how such physical effects combined with the PLANCK and the large scale magnetic field observation makes a large class of models viable and severely restricts the reheating equation of state parameter within a very narrow range of $0.01 < \omega_\mathrm{eff} < 0.27$, which is nearly independent of reheating scenarios we have considered.