The type IIB string axiverse and its low-energy phenomenology
Michele Cicoli, Mark Goodsell, Andreas Ringwald
TL;DR
The paper studies closed string axions in type IIB orientifold compactifications within the LARGE Volume Scenario (LVS), showing that a natural flux choice yields an axiverse comprising a QCD axion plus many light axion-like particles with logarithmically hierarchical masses. It derives axion masses and couplings to matter and gauge fields, analyzes conditions under which closed string axions solve the strong CP problem, and presents semi-realistic LVS constructions with a stable moduli sector and an untouched QCD axion candidate. It assesses the impact of inflationary dynamics on the LVS axiverse, surveys astrophysical, cosmological, and experimental constraints, and demonstrates how models can include extra light ALPs that could address certain astrophysical anomalies and be probed by next-generation helioscopes and LSW experiments. The work thus connects string compactifications to low-energy axion phenomenology, offering concrete predictions and search targets for forthcoming experiments.
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.