Holographic (De)confinement Transitions in Cosmological Backgrounds

TL;DR

This paper constructs holographic models of cosmological backgrounds with dark radiation and cosmological constant, analyzing their effects on confinement and deconfinement transitions in gauge theories via Wilson loops.

Contribution

It introduces new bulk solutions with cosmological backgrounds including dark radiation and boundary cosmological constant, and studies their impact on confinement phases.

Findings

Dark radiation promotes deconfinement.

Negative cosmological constant induces confinement.

Oscillating universe exhibits periodic confinement transitions.

Abstract

For type IIB supergravity with a running axio-dilaton, we construct bulk solutions which admit a cosmological background metric of Friedmann-Robertson-Walker type. These solutions include both a dark radiation term in the bulk as well as a four-dimensional (boundary) cosmological constant, while gravity at the boundary remains non-dynamical. We holographically calculate the stress-energy tensor, showing that it consists of two contributions: The first one, generated by the dark radiation term, leads to the thermal fluid of N = 4 SYM theory, while the second, the conformal anomaly, originates from the boundary cosmological constant. Conservation of the boundary stress tensor implies that the boundary cosmological constant is time-independent, such that there is no exchange between the two stress-tensor contributions. We then study (de)confinement by evaluating the Wilson loop in these backgrounds. While the dark radiation term favours deconfinement, a negative cosmological constant drives the system into a confined phase. When both contributions are present, we find an oscillating universe with negative cosmological constant which undergoes periodic (de)confinement transitions as the scale of three space expands and re-contracts.