Gauge Fields and Inflation

TL;DR

This review explores the role of gauge fields during cosmic inflation, analyzing their theoretical implications and observational signatures, including effects on the CMB and primordial magnetic fields.

Contribution

It provides a comprehensive overview of gauge field models in inflation, highlighting their impact on isotropy, cosmic no-hair theorem violations, and magnetic field generation.

Findings

Gauge fields can be active during inflation, affecting cosmic isotropy.

Models show both violation and preservation of the cosmic no-hair theorem.

Gauge fields may source primordial magnetic fields observable today.

Abstract

The isotropy and homogeneity of the cosmic microwave background (CMB) favors "scalar driven" early Universe inflationary models. Non-scalar fields, and in particular gauge fields, are on the other hand commonplace in all high energy particle physics models proposed to be at work at the upper bound on energy scale of inflation set by the current CMB observations. In this review we consider the role and consequences, theoretical and observational, that gauge fields can have during inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main class of models with gauge fields in the background, models which show violation of cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.