Large volume susy breaking with a solution to the decompactification problem

TL;DR

This paper proposes a mechanism in heterotic string models with large extra dimensions that avoids decompactification issues by utilizing a specific supersymmetry breaking pattern, resulting in controlled gauge coupling running and suppressed vacuum energy contributions.

Contribution

It introduces a novel approach to large volume SUSY breaking in heterotic strings that preserves perturbative control and addresses the decompactification problem through specific orbifold constructions.

Findings

The mechanism restores N=4 supersymmetry at the boundary of moduli space.

Twisted sectors with no fixed points distribute in non-aligned N=2 orbits.

Vacuum energy contributions are mainly from N=4 to N=0 breaking, with suppressed N=2 sectors.

Abstract

We study heterotic ground states in which supersymmetry is broken by coupling the momentum and winding charges of two large extra dimensions to the R-charges of the supersymmetry generators. The large dimensions give rise to towers of heavy string thresholds that contribute to the running of the gauge couplings. In the general case, these contributions are proportional to the volume of the two large dimensions and invalidate the perturbative string expansion. The problem is evaded if the susy breaking sectors arise as a spontaneously broken phase of N=4 -> N=2 -> N=0 supersymmetry, provided that N=4 supersymmetry is restored on the boundary of the moduli space. We discuss the mechanism in the case of Z_2 x Z_2 orbifolds, which requires that the twisted sector that contains the large extra dimensions has no fixed points. We analyse the full string partition function and show that the twisted sectors distribute themselves in non-aligned N=2 orbits, hence preserving the solution to the string decompactification problem. Remarkably, we find that the contribution to the vacuum energy from the N=2 -> N=0 sectors is suppressed, and the only substantial contribution arises from the breaking of the N=4 sector to N=0.