Searching for axion stars and Q-balls with a terrestrial magnetometer network

TL;DR

This paper proposes using a global network of atomic magnetometers to detect encounters with axion stars and Q-balls, promising a new method to identify dark matter candidates through terrestrial measurements.

Contribution

It demonstrates that terrestrial magnetometer networks can detect axion stars and Q-balls within certain mass and radius ranges, expanding the search for dark matter.

Findings

Detection rate can be at least once per year for certain objects.

Magnetometers are sensitive enough to detect pseudoscalar couplings during encounters.

Broad parameter space of unexplored dark matter candidates can be probed.

Abstract

Light (pseudo-)scalar fields are promising candidates to be the dark matter in the Universe. Under certain initial conditions in the early Universe and/or with certain types of self-interactions, they can form compact dark-matter objects such as axion stars or Q-balls. Direct encounters with such objects can be searched for by using a global network of atomic magnetometers. It is shown that for a range of masses and radii not ruled out by existing observations, the terrestrial encounter rate with axion stars or Q-balls can be sufficiently high (at least once per year) for a detection. Furthermore, it is shown that a global network of atomic magnetometers is sufficiently sensitive to pseudoscalar couplings to atomic spins so that a transit through an axion star or Q-ball could be detected over a broad range of unexplored parameter space.