The type IIB string axiverse and its low-energy phenomenology (1206.0819v2)

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.

• The paper demonstrates that LVS moduli stabilization yields a rich axiverse of light axion-like particles with logarithmically hierarchical masses.
• It provides detailed calculations of axion masses and couplings, linking theoretical predictions with experimental and astrophysical constraints.
• The study highlights axions' potential to resolve the strong CP problem and act as viable dark matter candidates for future experiments.

The Type IIB String Axiverse and Its Low-Energy Phenomenology

This paper, authored by Michele Cicoli, Mark D. Goodsell, and Andreas Ringwald, presents an in-depth exploration of axions within the framework of Type IIB string theory. Specifically, the paper focuses on axions emerging from Type IIB orientifold compactifications, emphasizing those stabilized through the moduli stabilization process known as the LARGE Volume Scenario (LVS).

In this context, the concept of an "axiverse" is central, referring to the potential existence of numerous light axion-like particles (ALPs) in addition to the well-known QCD axion. These ALPs manifest with logarithmically hierarchical masses and may couple to various fields, influencing both theoretical and experimental aspects of particle physics.

Key Findings and Contributions

1. Moduli Stabilization Mechanism:

The paper highlights the LARGE Volume Scenario as a robust environment for axiverse realization. The authors detail how natural values of background fluxes can stabilize moduli, leveraging non-perturbative effects on a singular del Pezzo divisor and perturbative $\alpha'$ corrections, yielding an axiverse with many light axions.

1. Axion Mass Spectrum:

The paper provides thorough calculations of axion masses and their couplings, revealing that these ALPs exhibit a hierarchy of masses due to the logarithmic structure of their potential. Such a mass spectrum enriches the phenomenological possibilities of the theory.

1. Experimental and Astrophysical Constraints:

A comprehensive treatment of potential experimental and astrophysical constraints on the LVS axiverse is conducted. This includes an analysis of constraints from beam dumps, astrophysical observations, and ongoing experimental searches such as those for solar axions and in light-shining-through-a-wall (LSW) experiments.

1. Cosmological Implications:

The discussion outlines the cosmological significance of these axions, touching upon aspects like the strong CP problem resolution, dark matter candidates, and potential links to various cosmological and astrophysical anomalies.

Implications and Future Prospects

The implications of this research extend both theoretically and practically. From a theoretical standpoint, the existence of an axiverse within string frameworks enhances understanding of axion physics beyond the traditional scope, potentially providing leverage to tackle longstanding issues such as the strong CP problem.

Practically, future experimental searches can leverage the insights provided on axion couplings and mass predictions to refine detection strategies. The paper suggests that axions and ALPs, particularly with intermediate-scale decay constants, could be viable targets for the next generation of helioscopes and LSW experiments.

Conclusion

The investigation of axions within the LVS of Type IIB string theory uncovers promising terrain for theoretical exploration and experimental inquiry. By situating axions within a broader axiverse context, the paper advances the field toward a more comprehensive understanding of light particles in string theory, fostering new potential synergies between string phenomenology and experimental particle physics. Future research and experimentation will no doubt continue to test and refine these concepts, pushing the boundaries of knowledge in high-energy physics.