Axions in the Landscape and String Theory

TL;DR

This paper explores the prevalence and survival of axions within string theory frameworks, analyzing how different supersymmetry breaking scales influence moduli stabilization and the emergence of light axions.

Contribution

It systematically classifies moduli fixing mechanisms across various supersymmetry breaking scales and assesses the plausibility of light axions in each scenario.

Findings

Light axions are plausible at intermediate and high supersymmetry breaking scales.

Moduli fixing mechanisms vary with the scale of supersymmetry breaking.

Large extra dimensions are revisited in the context of axion and moduli stabilization.

Abstract

While axions seem ubiquitous in critical string theories, whether they might survive in any string theoretic description of nature is a difficult question. With some mild assumptions, one can frame the issues in the case that there is an approximate supersymmetry below the underlying string scale. The problem of axions is then closely tied to the question of how moduli are fixed. We consider, from this viewpoint, the possibility that supersymmetry is broken at an intermediate scale, as in "gravity mediation," at a low scale, as in gauge mediation, and at a very high scale, to model the possibility that there is no low energy supersymmetry. Putative mechanisms for moduli fixing can then be systematically classified, and at least for intermediate and high scale breaking, light axions appear plausible. In the course of this work, we are lead to consider aspects of moduli fixing and supersymmetry breaking, and we revisit the possibility of very large extra dimensions.