Primordial magnetic field from non-inflationary cosmic expansion in Horava-Lifshitz gravity

TL;DR

This paper proposes a novel mechanism within Horava-Lifshitz gravity for generating large-scale primordial magnetic fields during non-inflationary cosmic expansion, addressing the origin of cosmic magnetism.

Contribution

It introduces a new magnetic field generation process leveraging Horava-Lifshitz gravity's UV properties, allowing conformal symmetry breaking without inflation.

Findings

Generated magnetic fields can serve as seeds for cosmic dynamo.

The mechanism produces sufficiently large magnetic fields without significant backreaction.

Results are consistent with observational constraints from MAGIC and FERMI.

Abstract

The origin of large-scale magnetic field in the universe is one of the greatest mysteries in modern cosmology. We present a new mechanism for generation of large-scale magnetic field, based on the power-counting renormalizable theory of gravitation recently proposed by Horava. Contrary to the usual case in general relativity, the U(1) gauge symmetry of a Maxwell action in this theory permits terms breaking conformal invariance in the ultraviolet. Moreover, for high frequency modes, the anisotropic scaling intrinsic to the theory inevitably makes the sound horizon far outside the Hubble horizon. Consequently, non-inflationary cosmic expansion in the early universe naturally generates super-horizon quantum fluctuations of the magnetic field. Specializing our consideration to the case with the dynamical critical exponent $z=3$, we show an explicit set of parameters for which (i) the amplitude of generated magnetic field is large enough as a seed for the dynamo mechanism; (ii) backreaction to the cosmic expansion is small enough; and (iii) the high-energy dispersion relation is consistent with the most recent observational limits from MAGIC and FERMI.