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.
Bibliographical noteFunding Information:
The authors are sincerely grateful to Andrei Derevianko, Konstantin Zioutas, Jason Stalnaker, and Chris Pankow for useful discussions. D. F. J. K. acknowledges the support of the National Science Foundation under Grant No. PHY-1707875. D. F. J. K., D. B., and A. Wickenbrock acknowledge the support of the Simons and Heising-Simons Foundations. Y. V. S. was supported by the Humboldt Research Fellowship. The work of J. E. was supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program; the SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract No. de-sc0014664. D. B. acknowledges the support of the European Research Council and DFG Koselleck. M. P. is supported in part by NSERC, Canada, and research at the Perimeter Institute is supported in part by the Government of Canada through Natural Sciences and Engineering Research Council of Canada (NSERC) and by the Province of Ontario through Ministry of Economic Development and Trade (MEDT). S. P. acknowledges the support of the Polish National Science Centre within the Opus program.
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