Cosmological particle production in emergent rainbow spacetimes

TL;DR

This paper explores how emergent rainbow spacetimes, with momentum-dependent metrics due to Lorentz invariance breaking, affect cosmological particle production, using Bose gases as analogue models and analyzing deviations from standard predictions.

Contribution

It introduces a model of emergent rainbow spacetimes with Lorentz invariance violation and studies their impact on cosmological particle production in analogue Bose gas systems.

Findings

Low-energy modes are unaffected by rainbow effects.

Some modes re-enter the horizon during inflation.

Ultraviolet modes are insensitive to expansion.

Abstract

We investigate cosmological particle production in spacetimes where Lorentz invariance emerges in the infrared limit, but is explicitly broken in the ultraviolet regime. Our specific model focuses on the boost subgroup that supports CPT invariance and results in a momentum-dependent dispersion relation. Motivated by previous studies on spacetimes emerging from a microscopic substrate, we show how these modifications naturally lead to momentum-dependent rainbow metrics. Firstly, we investigate the possibility of reproducing cosmological particle production in spacetimes emerging from real Bose gases. We have studied the influence of non-perturbative ultraviolet corrections in time-dependent analogue spacetimes, leading to momentum-dependent emergent rainbow spacetimes. Within certain limits the analogy is sufficiently good to simulate relativistic quantum field theory in time-dependent classical backgrounds, and the quantum effects are approximately robust against the model-dependent modifications. Secondly, we analyze how significantly the particle production process deviates from the common picture. While very low-energy modes do not see the difference at all, some modes "re-enter the Hubble horizon" during the inflationary epoch, and extreme ultraviolet modes are completely insensitive to the expansion.