Title: Searching for axion stars and Q-balls with a terrestrial magnetometer network,
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.