String Theory and Quintessence

TL;DR

The paper argues that string theory, as traditionally formulated with S-matrix-like observables, struggles to describe accelerating universes. It analyzes observables across flat, AdS, and cosmological backgrounds, concluding that future horizons in quintessence-like scenarios obstruct a standard S-matrix description. By examining Q-space with -1<w<-1/3, it shows the resulting causal diamonds and horizons undermining observable, global data, and it derives a no-go result: single-field potentials leading to eternal quintessence cannot asymptotically approach a supersymmetric vacuum with ∂φW=0. The work suggests that preserving a consistent string-theoretic description of our accelerating universe may require novel observables or a revised framework beyond the current S-matrix paradigm.

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.

Figures (5)

• Figure 1: Causal structure of FRW spacetime.
• Figure 2: Causal structure of deSitter spacetime.
• Figure 3: Causal structure of Schwarzschild spacetime.
• Figure 4: Causal structure of a spatially flat Universe dominated by $-1<w<-1/3$ matter.
• Figure 5: Causal structure of a spatially flat Universe dominated by $w=-1/3$ matter.