String Theory and Quintessence

TL;DR

This paper explores the challenges of formulating string theory in an accelerating universe, focusing on obstacles related to defining observable quantities and the implications of quintessence models with future horizons.

Contribution

It analyzes the limitations of current string theory frameworks in describing accelerating universes, especially regarding S-matrix formulation and vacuum stability.

Findings

Quintessence models with -1 < w < -1/3 have future horizons, complicating S-matrix definitions.

In certain supersymmetric theories, a system cannot settle into a zero-energy vacuum during acceleration.

Describing an eternally accelerating universe poses significant challenges for existing string theory formulations.

Abstract

We discuss the obstacles for defining a set of observable quantities analogous to an S-matrix which are needed to formulate string theory in an accelerating universe. We show that the quintessence models with the equations of state $-1 < w <-1/3$ have future horizons and may be no better suited to an S-matrix or S-vector description. We also show that in a class of theories with a stable supersymmetric vacuum, a system cannot relax into a zero-energy supersymmetric vacuum while accelerating if the evolution is dominated by a single scalar field with a stable potential. Thus describing an eternally accelerating universe may be a challenge for string theory as presently defined.