A stringy perspective on the coincidence problem

TL;DR

This paper explores how string theory predicts dark energy may lead to an eventual universe-ending phase transition, with a tower of heavy states triggering this process after a finite timescale, impacting cosmological models.

Contribution

It introduces a string-inspired model where a tower of heavy states causes a breakdown of dark energy dominance, providing a novel perspective on the coincidence problem and universe's fate.

Findings

Dark energy likely signals universe's end via decompactification.

A tower of heavy states triggers a phase transition after a few hundred Hubble times.

Overproduction of particles overwhelms quintessence, ending dark energy domination.

Abstract

We argue that, for generic string compactifications, dark energy is likely to signal the beginning of the end of our universe, perhaps even through decompactification, with possible implications for the cosmological coincidence problem. Thanks to the scarcity (absence?) of stable de Sitter vacua, dark energy in string theory is assumed to take the form of a quintessence field in slow roll. As it rolls, a tower of heavy states will generically descend, triggering an apocalyptic phase transition in the low energy cosmological dynamics after at most a few hundred Hubble times. As a result, dark energy domination cannot continue indefinitely and there is at least a percentage chance that we find ourselves in the first Hubble epoch. We use a toy model of quintessence coupled to a tower of heavy states to explicitly demonstrate the breakdown in the cosmological dynamics as the tower becomes light. This occurs through a large number of corresponding particles being produced after a certain time, overwhelming quintessence. We also discuss some implications for early universe inflation.