A1 Journal article (refereed)
Merger of dark matter axion clumps and resonant photon emission (2020)

Hertzberg, M. P., Li, Y., & Schiappacasse, E. D. (2020). Merger of dark matter axion clumps and resonant photon emission. Journal of Cosmology and Astroparticle Physics, 2020(7), Article 067. https://doi.org/10.1088/1475-7516/2020/07/067

JYU authors or editors

Publication details

All authors or editors: Hertzberg, Mark P.; Li, Yao; Schiappacasse, Enrico D.

Journal or series: Journal of Cosmology and Astroparticle Physics

eISSN: 1475-7516

Publication year: 2020

Volume: 2020

Issue number: 7

Article number: 067

Publisher: Institute of Physics

Publication country: United Kingdom

Publication language: English

DOI: https://doi.org/10.1088/1475-7516/2020/07/067

Publication open access: Not open

Publication channel open access: 

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/71776

Publication is parallel published: https://arxiv.org/abs/2005.02405

Abstract

A portion of light scalar dark matter, especially axions, may organize into gravitationally bound clumps (stars) and be present in large number in the galaxy today. It is therefore of utmost interest to determine if there are novel observational signatures of this scenario. Work has shown that for moderately large axion-photon couplings, such clumps can undergo parametric resonance into photons, for clumps above a critical mass Mਮc determined precisely by some of us in ref. [1]. In order to obtain a clump above the critical mass in the galaxy today would require mergers. In this work we perform full 3-dimensional simulations of pairs of axion clumps and determine the conditions under which mergers take place through the emission of scalar waves, including analyzing head-on and non-head-on collisions, phase dependence, and relative velocities. Consistent with other work in the literature, we find that the final mass from the merger Mਮfinal≈ 0.7(Mਮ1+Mਮ2) is larger than each of the original clump masses (for Mਮ1∼ Mਮ2). Hence, it is possible for sub-critical mass clumps to merge and become super-critical and therefore undergo parametric resonance into photons. We find that mergers are expected to be kinematically allowed in the galaxy today for high Peccei-Quinn scales, which is strongly suggested by unification ideas, although the collision rate is small. While mergers can happen for axions with lower Peccei-Quinn scales due to statistical fluctuations in relative velocities, as they have a high collision rate. We estimate the collision and merger rates within the Milky Way galaxy today. We find that a merger leads to a flux of energy on earth that can be appreciable and we mention observational search strategies.

Keywords: astrophysics; cosmology; dark matter; elementary particles; photons

Contributing organizations

Ministry reporting: Yes

Reporting Year: 2020

JUFO rating: 1