Banks-Zaks Cosmology, Inflation, and the Big Bang Singularity

TL;DR

This paper explores how Banks-Zaks theory influences cosmological evolution, proposing non-singular bouncing and cyclic universes that challenge traditional Big Bang models by violating classical energy conditions.

Contribution

It introduces a novel non-singular cosmological model based on Banks-Zaks theory's anomalous dimension, avoiding the Big Bang singularity without scalar fields.

Findings

Banks-Zaks theory leads to non-singular bouncing universes.

The model includes inflation without a Big Bang singularity.

Violates the Null Energy Condition near bounces.

Abstract

We consider the thermodynamical behavior of Banks-Zaks theory close to the conformal point in a cosmological setting. Due to the anomalous dimension, the resulting pressure and energy density deviate from that of radiation and result in various interesting cosmological scenarios. Specifically, for a given range of parameters one avoids the cosmological singularity. We provide a full "phase diagram" of possible Universe evolution for the given parameters. For a certain range of parameters, the thermal averaged Banks-Zaks theory alone results in an exponentially contracting universe followed by a non-singular bounce and an exponentially expanding universe, i.e. \textit{Inflation without a Big Bang singularity}, or shortly termed "dS Bounce". The temperature of such a universe is bounded from above and below. The result is a theory violating the classical Null Energy Condition (NEC). Considering the Banks-Zaks theory with an additional perfect fluid, yields an even richer phase diagram that includes the standard Big Bang model, stable single "normal" bounce, dS Bounce and stable cyclic solutions. The bouncing and cyclic solutions are with no singularities, and the violation of the NEC happens only near the bounce. We also provide simple analytical conditions for the existence of these non-singular solutions. Hence, within effective field theory, we have a new alternative non-singular cosmology based on the anomalous dimension of Bank-Zaks theory that may include inflation and without resorting to scalar fields.