Searching for axions and ALPs from string theory

TL;DR

This paper reviews the theoretical predictions and experimental prospects for detecting axions and axion-like particles from string theory compactifications, highlighting their potential as dark matter candidates and explanations for astrophysical anomalies.

Contribution

It provides a detailed analysis of the expected properties and phenomenology of string theory axions and ALPs, connecting string models with experimental searches.

Findings

Predicts the existence of a QCD axion with decay constant ~10^9-10^12 GeV.

Identifies additional ALPs with similar decay constants but lighter masses.

Suggests experimental searches could detect these axions and ALPs in the near future.

Abstract

We review searches for closed string axions and axion-like particles (ALPs) in IIB string flux compactifications. For natural values of the background fluxes and TeV scale gravitino mass, the moduli stabilisation mechanism of the LARGE Volume Scenario predicts the existence of a QCD axion candidate with intermediate scale decay constant, f_a ~ 10^9 ... 10^12 GeV, associated with the small cycles wrapped by the branes hosting the visible sector, plus a nearly massless and nearly decoupled ALP associated with the LARGE cycle. In setups where the visible sector branes are wrapping more than the minimum number of two intersecting cycles, there are more ALPs which have approximately the same decay constant and coupling to the photon as the QCD axion candidate, but which are exponentially lighter. There are exciting phenomenological opportunities to search for these axions and ALPs in the near future. For f_a ~ 10^11 ... 10^12 GeV, the QCD axion can be the dominant part of dark matter and be detected in haloscopes exploiting microwave cavities. For f_a ~ 10^9 ... 10^10 GeV, the additional ALPs could explain astrophysical anomalies and be searched for in the upcoming generation of helioscopes and light-shining-through-a-wall experiments.