TCC in the interior of moduli space and its implications for the string landscape and cosmology

TL;DR

This paper explores how the Trans-Planckian Censorship Conjecture (TCC) constrains scalar field solutions in string theory, impacting cosmological models and the feasibility of inflation within the string landscape.

Contribution

It demonstrates that solutions violating TCC do not approach the vacuum with zero particles, providing new constraints on scalar potentials in string theory and cosmology.

Findings

Solutions violating TCC do not reach the zero-particle vacuum.

TCC imposes nonlinear constraints on the string landscape.

Implications suggest inflation may be impossible in certain string scenarios.

Abstract

We consider the classical Friedmann-Robertson-Walker solutions that describe a universe undergoing a transition from an accelerating expansion phase in the past to an eternal decelerating expansion phase in the future, driven by a scalar field evolving in a potential energy landscape. We show that any solution for which the accelerating phase violates the Trans-Planckian Censorship Conjecture (TCC), even in the interior of moduli space, never approaches the asymptotic vacuum with zero particles. Based on the assumption that the effective field theory must be valid for the vacuum on the asymptotic boundary, as motivated by holography and string theory, we argue that (multi-field) scalar potentials with such solutions are disallowed, thus strengthening the case for TCC. In particular, the results imply a new set of complex and highly-nonlinear constraints across the entire string landscape which may make realizing inflation impossible.