The type IIB string axiverse and its low-energy phenomenology

TL;DR

This paper explores the phenomenology of closed string axions in type IIB compactifications, revealing a rich axiverse with a QCD axion and many light axion-like particles, and discusses their potential to solve the strong CP problem and explain astrophysical anomalies.

Contribution

It provides the first detailed analysis of the LVS axiverse's mass spectrum, couplings, and phenomenological implications, including explicit models with a viable QCD axion.

Findings

Identification of a hierarchical spectrum of axion masses

Derivation of axion couplings to matter and gauge fields

Models demonstrating the QCD axion can solve the strong CP problem

Abstract

We study closed string axions in type IIB orientifold compactifications. We show that for natural values of the background fluxes the moduli stabilisation mechanism of the LARGE Volume Scenario (LVS) gives rise to an axiverse characterised by the presence of a QCD axion plus many light axion-like particles whose masses are logarithmically hierarchical. We study the phenomenological features of the LVS axiverse, deriving the masses of the axions and their couplings to matter and gauge fields. We also determine when closed string axions can solve the strong CP problem, and analyse the first explicit examples of semi-realistic models with stable moduli and a QCD axion candidate which is not eaten by an anomalous Abelian gauge boson. We discuss the impact of the choice of inflationary scenario on the LVS axiverse, and summarise the astrophysical, cosmological and experimental constraints upon it. Moreover, we show how models can be constructed with additional light axion-like particles that could explain some intriguing astrophysical anomalies, and could be searched for in the next generation of axion helioscopes and light-shining-through-a-wall experiments.