Trans-Planckian Censorship and the Swampland

TL;DR

This paper introduces the Trans-Planckian Censorship Conjecture (TCC), a new Swampland condition asserting that sub-Planckian quantum fluctuations should not become classical, leading to constraints on cosmological potentials and forbidding long-lived de Sitter spaces.

Contribution

It proposes the TCC as a novel Swampland criterion, connecting quantum fluctuation behavior with constraints on scalar potentials in cosmology.

Findings

TCC imposes an upper bound on the slope of scalar potentials.

It constrains the decay rate of potentials with an exponential bound.

TCC forbids long-lived metastable de Sitter spaces.

Abstract

In this paper, we propose a new Swampland condition, the Trans-Planckian Censorship Conjecture (TCC), based on the idea that in a consistent quantum theory of gravity sub-Planckian quantum fluctuations should remain quantum and never become larger than the Hubble horizon and freeze in an expanding universe. TCC leads to conditions that are similar to the refined dS Swampland conjecture. For example, applied to the case of cosmologies driven only by a scalar field, the TCC imposes an upper bound of $2/\sqrt{d-2}$ on the asymptotic value of $|V'|/V$. Additionally, it implies that a monotonically decreasing potential across $[\phi_1,\phi_2]$ satisfies $V(\phi_2)\leq A\cdot\exp(-2(\phi_2-\phi_1))/\sqrt{(d-1)(d-2)})$ for some $\mathcal{O}(1)$ constant $A$. Like the dS Swampland conjecture, the TCC forbids long-lived meta-stable dS spaces, but allows sufficiently short-lived ones.