The Cosmological Constant and Dark Dimensions from Non-Supersymmetric Strings

TL;DR

This paper constructs a string theory model where particle physics vacuum energy contributions cancel, gravity propagates in large extra dimensions, and moduli are stabilized, providing insights into dark energy and large extra dimensions.

Contribution

It introduces a novel string theory setup with canceling vacuum energy contributions and stabilized large extra dimensions, combining Scherk-Schwarz and brane supersymmetry breaking mechanisms.

Findings

Particle physics vacuum energy cancels exactly.

Gravity propagates in large, micron-sized extra dimensions.

Moduli stabilization leads to exponentially small vacuum energy.

Abstract

We present a string theory construction in which the particle physics contributions to the one-loop vacuum energy exactly cancel, whilst the gravitational contributions are suppressed in the size of one or two large extra dimensions. This provides an ultraviolet realisation of the Dark Dimension and Supersymmetric Large Extra Dimensions scenarios, with, moreover, an explanation as to why the Standard Model contributions to the vacuum energy cancel without the need of eV mass-splittings. Gravity propagates in micron sized dark dimension(s), whilst the visible and hidden sectors are supported on D-branes. Supersymmetry is broken in the dark dimension(s) \`a la Scherk-Schwarz, whereas supersymmetry is broken at the string scale, \`a la Brane Supersymmetry Breaking, in the D-branes sector, without inducing tadpoles, similarly to a different construction proposed a long time ago by Angelantonj and Antoniadis. Vacuum energy from the visible sector is cancelled by the vacuum energy of the hidden sector branes. We also discuss moduli stabilization in this set-up, finding that the interplay between the Scherk-Schwarz one-loop contribution and non-perturbative effects can fix the size of the dark dimension(s) to be exponentially large in the inverse string-coupling, leading to an exponentially small total vacuum energy, with all moduli stabilised in a dS saddle.