Cosmology with non-conformal holographic matter

TL;DR

This paper explores how a strongly coupled quantum field undergoing RG flow from UV to IR affects cosmological evolution, revealing intermediate behavior between matter and radiation due to non-conformal effects.

Contribution

It introduces a holographic model of a non-conformal quantum field and analyzes its impact on cosmology, highlighting the intermediate equation of state during RG flow.

Findings

The equation of state parameter w dips below 1/3 at intermediate temperatures.

The energy density dilutes less rapidly during expansion compared to a pure radiation field.

The cosmological expansion rate increases due to the RG flow effects.

Abstract

We investigate the effect on cosmological evolution of a strongly coupled quantum field that undergoes renormalization group flow from a UV CFT to an IR CFT. The field theory is defined by perturbation of a holographic CFT by a relevant operator associated with a bulk scalar field that evolves from a local maximum of its potential near the boundary to a local minimum of its potential deep in the bulk. By studying the gravity solutions dual to this theory on $\mathbb{R}^3 \times S^1$, we find that the equation of state parameter $w$ for the field theory has the conformal behavior $w=1/3$ for high and low temperatures, but dips to lower values for intermediate temperatures. Thus, at scales where the field theory has significant scale-dependence, its effect on cosmological evolution is intermediate between matter and radiation. Compared to the unperturbed UV CFT (which acts as radiation), the energy density experiences less dilution during the expansion as a result of the RG flow, and the rate of expansion is greater.