Towards string theory expectations for photon couplings to axionlike particles

James Halverson,Gustavo Salinas,Cody Long,Brent Nelson

doi:10.1103/physrevd.100.106010

James Halverson, Gustavo Salinas + Show 2 more

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https://doi.org/10.1103/physrevd.100.106010

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Abstract

ALP-photon couplings are modeled in large ensembles of string vacua and random matrix theories. In all cases, the effective coupling increases polynomially in the number of ALPs, of which hundreds or thousands are expected in the string ensembles, many of which are ultralight. The expected value of the couplings $g_{a\gamma\gamma}\simeq 10^{-12}\text{GeV}^{-1} - 10^{-10}\text{GeV}^{-1}$ provide viable targets for future x-ray telescopes and axion helioscopes, and in some cases are already in tension with existing data.

Highlights

If string theory is the correct theory of quantum gravity, one of its vacua must realize the photon of classical electromagnetism
In this paper we studied distributions of axionlike particle (ALP)-photon couplings in ensembles of string compactifications and random matrix theories
Since hundreds or thousands of axionlike particles typically arise in string compactifications, we studied the scaling of the effective gaγγ distribution with N and its extrapolation to the expected value of N in a given ensemble

Summary

Introduction

If string theory is the correct theory of quantum gravity, one of its vacua must realize the photon of classical electromagnetism. Uncharged spin zero particles must couple to the electromagnetic field strength, since all couplings in string theory are determined by vacuum expectation values (VEVs) of scalar fields. This applies to the usual parity even operator FμνFμν, and the parity odd operator, requiring the existence of a coupling L ⊃ −. The exclusions depend critically on whether the ALP is assumed to be a sizable fraction of the dark matter and experimental limitations affecting the accessible mass range. Since dark matter in string theory is often multicomponent (e.g., [12,13]) and many ALPs are expected to be ultralight, but not yet in any fixed mass

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