Relaxion and how to detect it

We show that relaxion, that addresses the hierarchy problem, can account for the observed dark matter (DM) relic density. The setup is similar to the case of axion DM models topped with a dynamical misalignment mechanism. The phenomenology of this class of models is quite unique, as it implies that, on the one hand, we are surrounded by a time-dependent axion-like field, while, on the other hand, its background behaves as a time-dependent oscillating scalar field due to the relaxion-Higgs mixing. We also consider the possibility that the relaxion forms gravitationally bound objects that we denote as relaxion stars. The density of these stars would be higher than that of the local dark matter density, resulting in enhanced signals for table-top detectors. Furthermore, we raise the possibility that these objects may be trapped by an external gravitational potential, such as that of the Earth or the Sun. This leads to formation of relaxion halos of even greater density. We discuss several interesting implications of relaxion halos, as well as detection strategies to probe them. If time permits, we will discuss how presence of a relaxion halo can affect the sensitivity of the present and near future axion-dark matter experiments. While satisfying all the present experimental constraints, such halos may offer a unique way to significantly improve the sensitivity to the ALP parameter space. We demonstrate this with several distinct types of dark matter experiments. Based on: https://arxiv.org/abs/1810.01889 and https://arxiv.org/abs/1902.08212