The Acceleration of the Universe, a Challenge for String Theory
W. Fischler, A. Kashani-Poor, R. McNees, S. Paban
TL;DR
The paper addresses whether dynamical dark energy in the form of quintessence inevitably produces horizons that challenge string theory. By analyzing flat FRW cosmologies with scalar fields and several potentials, it shows that many quintessence models produce eternal acceleration with finite conformal time, and hence event horizons, similar to asymptotic de Sitter space. It discusses exponential and inverse power-law potentials with tracker or runaway behavior that asymptotically approach $p=-\rho$, reinforcing the horizon issue and the associated questions about the string-theory observables and S-matrix. The work highlights a fundamental tension between late-time acceleration and conventional string-theory formulations, underscoring the need for new ideas or loopholes to reconcile these frameworks.
Abstract
Recent astronomical observations indicate that the universe is accelerating. We argue that generic quintessence models that accommodate the present day acceleration tend to accelerate eternally. As a consequence the resulting spacetimes exhibit event horizons. Hence, quintessence poses the same problems for string theory as asymptotic de Sitter spaces.