Momentum and Matter Matter for Axion Dark Matter Matters on Earth

TL;DR

This paper explores how Earth's matter influences axion dark matter detection experiments, revealing that matter effects can both diminish axion signals and enhance field gradients, impacting experimental sensitivities.

Contribution

It provides a detailed analysis of matter effects on axion dark matter signals, highlighting their significance for experimental searches on Earth.

Findings

Matter effects can reduce axion field amplitude for certain parameter spaces.

Axion field gradients can be enhanced along Earth's radial direction.

Experiments sensitive to lighter axions with stronger couplings are more affected.

Abstract

We investigate the implications of matter effects to searches for axion Dark Matter on Earth. The finite momentum of axion Dark Matter is crucial to elucidating the effects of Earth on both the axion Dark Matter field value and its gradient. We find that experiments targeting axion couplings compatible with canonical solutions of the strong CP puzzle are likely not affected by Earth's matter effects. However, experiments sensitive to lighter axions with stronger couplings can be significantly affected, with a significant part of the parameter space suffering from a reduced axion field value, and therefore decreased experimental sensitivity. In contrast, the spatial gradient of the axion field can be enhanced along Earth's radial direction, with important implications for ongoing and planned experiments searching for axion Dark Matter.