Waiting for Inflation: A New Initial State for the Universe

TL;DR

This paper introduces a novel initial state for the universe involving a lingering phase at constant temperature before inflation, addressing the singularity problem and potentially leaving observable imprints.

Contribution

It proposes a new cosmological initial state with a lingering phase that transitions into inflation, incorporating string theory and quantum gravity considerations.

Findings

Models can produce observable spatial curvature in the CMB.

Lingering phase can arise with or without spatial curvature in quantum gravity theories.

The string theory dilaton plays a key role in the dynamics.

Abstract

We propose a cosmological lingering phase for the initial state prior to inflation which would help address the singularity problem of inflation. The universe begins with a constant (Hagedorn) temperature and then transitions into an inflationary universe while preserving the Null Energy Condition (NEC). In such a universe time is presumably emergent, calling the age of the universe into question. We first consider the phase space of positive spatial curvature models within General Relativity and with matter sources that respect the NEC. Depending on the duration of the post-lingering inflation these models can produce a small amount of observable spatial curvature in the Cosmic Microwave Background. We also discuss how lingering can arise with or without spatial curvature in theories of quantum gravity when considering the thermodynamic scaling of particles and its impact on the early universe. The string theory dilaton is essential to the dynamics. There are many open questions that remain.