Abstract
We discuss the sensitivity of the present and near-future axion dark matter experiments to a halo of axions or axion-like particles gravitationally bound to the Earth or the Sun. Such halos, assuming they are formed, can be searched for in a wide variety of experiments even when the axion couplings to matter are small, while satisfying all the present experimental bounds on the local properties of dark matter. The structure and coherence properties of these halos also imply novel signals, which can depend on the latitude or orientation of the detector. We demonstrate this by analyzing the sensitivity of several distinct types of axion dark matter experiments.
Highlights
Between Earth and these small-scale objects should be large enough such that one may expect several transient signals within an experimental timescale
We discuss the sensitivity of the present and near-future axion dark matter experiments to a halo of axions or axion-like particles gravitationally bound to the Earth or the Sun
The structure and coherence properties of these halos imply novel signals, which can depend on the latitude or orientation of the detector. We demonstrate this by analyzing the sensitivity of several distinct types of axion dark matter experiments
Summary
We consider compact astrophysical objects composed of ALPs. In particular, we focus on scenarios where such objects are gravitationally bounded to the Earth or the Sun; we call such an object a Solar or Earth axion halo. For the Earth halo, both gradient components are constant in time; the radial gradient can be maximized by choice of orientation of the experimental apparatus with respect to the surface of the Earth, whereas the tangential gradient depends in addition on the latitude of the detector, as the relative velocity vr⊕el is faster at the equator and goes to zero at Earth’s poles. The existence of separate radial and tangential gradients is a unique prediction of the axion halo model This implies a method to distinguish a bound axion halo from background DM by using directional information, as the detector orientation and its location can modify the signal; this is possible even if the axion halo has the same mass density as the background DM.
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