We propose a new thermal freeze-out mechanism that results in dark matter masses exceeding the unitarity bound by many orders of magnitude, without violating perturbative unitarity or modifying the standard cosmology. The process determining the relic abundance is χζ†→ζζ, where χ is the dark matter candidate. For mζ<mχ<3mζ, χ is cosmologically long-lived and scatters against the exponentially more abundant ζ. Therefore, such a process allows for exponentially heavier dark matter for the same interaction strength as a particle undergoing ordinary 2→2 freeze-out, or equivalently, exponentially weaker interactions for the same mass. We demonstrate this mechanism in a leptophilic dark matter model, which allows for dark matter masses up to 109 GeV.
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We would like to thank Asher Berlin, Timothy Cohen, Timon Emken, Rouven Essig, Michael Geller, Roni Harnik, Yonit Hochberg, Hyungjin Kim, Gordan Krnjaic, Sam McDermott, Mukul Sholapurkar, and Tomer Volansky for useful discussions. The work of E. D. K. is supported by the Zuckerman STEM Leadership Program. The work of E. K. and E. D. K. is supported by the Israel Science Foundation (Grant No. 1111/17), and by the I-CORE Program of the Planning Budgeting Committee (Grant No. 1937/12). The work of E. K. is further supported by the Binational Science Foundation (Grant No. 2016153). N. J. O. is grateful to the Azrieli Foundation for the support of an Azrieli Fellowship. N. L. would like to thank the Milner Foundation for the support of a Milner Fellowship. J. T. R. is supported by NSF CAREER Grant No. PHY-1554858 and NSF Grant No. PHY-1915409. E. D. K., E. K., and N. J. O. would like to acknowledge the GGI Institute for Theoretical Physics for enabling them to complete a significant portion of this work. J. T. R. acknowledges hospitality from the Aspen Center for Physics, which is supported by the NSF Grant No. PHY-1607611.
© 2021 authors. Published by the American Physical Society.