Spectator Higgs, large-scale gauge fields and the non-minimal coupling to gravity

TL;DR

This paper investigates how the non-minimal coupling of the Higgs field to gravity influences large-scale gauge fields and their potential role in primordial magnetogenesis, revealing critical bounds on the coupling strength.

Contribution

It introduces a comprehensive analysis of the effects of non-minimal Higgs-gravity coupling on gauge field generation and establishes new bounds on the coupling parameter.

Findings

Non-minimal coupling significantly affects hypercharge and electromagnetic field evolution.

Overcritical gauge fields are produced when coupling exceeds one fourth.

Magnetic fields can reach strengths relevant for primordial magnetogenesis, up to 10^{-20} G.

Abstract

Even if the Higgs field does not affect the evolution of the background geometry, its massive inhomogeneities induce large-scale gauge fields whose energy density depends on the slow-roll parameters, on the effective scalar mass and, last but not least, on the dimensionless coupling to the space-time curvature. Since the non-Abelian gauge modes are screened, the non-minimal coupling to gravity predominantly affects the evolution of the hypercharge and electromagnetic fields. While in the case of minimal coupling the obtained constraints are immaterial, as soon as the coupling increases beyond one fourth the produced fields become overcritical. We chart the whole parameter space of this qualitatively new set of bounds. Whenever the limits on the curvature coupling are enforced, the magnetic field may still be partially relevant for large-scale magnetogenesis and exceed $10^{-20}$ G for the benchmark scale of the protogalactic collapse.