Abstract
We present a class of models in which the coupling of the photon to an ultralight scalar field that has a time-dependent vacuum expectation value causes the fine structure constant to oscillate in time. The scalar field is assumed to constitute all or part of the observed dark matter. Its mass is protected against radiative corrections by a discrete ${\mathbb{Z}}_{N}$ exchange symmetry that relates the Standard Model to several copies of itself. The abundance of dark matter is set by the misalignment mechanism. We show that the oscillations in the fine structure constant are large enough to be observed in current and near-future experiments.
Highlights
With the discovery of the Higgs boson [1,2], the Standard Model (SM) of particle physics is complete
Moduli are among the most well-motivated and compelling dark matter candidates [4,5,6,7,8]. They often arise in ultraviolet-complete theories such as string theory, where their vacuum expectation values (VEVs) play a role in determining the values of fundamental parameters such as the fine structure constant
We present a framework in which the modulus that controls the fine structure constant can naturally remain ultralight while constituting all of the observed dark matter in the universe
Summary
With the discovery of the Higgs boson [1,2], the Standard Model (SM) of particle physics is complete. The modulus begins to oscillate about its minimum, contributing to the energy density of the universe as a component of dark matter This framework, termed the misalignment mechanism [9], is a natural way of. A very attractive feature of this framework is that, for certain ranges of the modulus mass and couplings, the misalignment mechanism naturally allows the modulus to constitute all of the observed dark matter. Finite temperature effects can drastically alter the behavior of the modulus at early times They can act either to reduce or increase the abundance of dark matter by relaxing the modulus to the minimum or maximum of its potential at high temperatures.
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