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SUMMARY:WIMP Meets ALP: Coherent Freeze-Out of Dark Matter
DTSTART;VALUE=DATE-TIME:20260810T065000Z
DTEND;VALUE=DATE-TIME:20260810T071500Z
DTSTAMP;VALUE=DATE-TIME:20260824T144818Z
UID:indico-contribution-2672@indico.itp.ac.cn
DESCRIPTION:Speakers: Bingrong Yu (Cornell University)\nThe microscopic na
 ture of dark matter is the major open question in science. Weakly-Interact
 ing Massive Particles (WIMPs) and Axion-Like Particles (ALPs) are the two 
 most theoretically motivated dark matter candidates. Thousands of papers c
 onsider them separately. We point out that if both species are present in 
 the theory\, even a tiny (Planck-suppressed) interaction between them coul
 d lead to drastic modifications of their dynamics in the early universe.\n
 \nSpecifically\, we consider the cosmological history of a fermionic WIMP 
 coupled to a light ALP via a quadratic coupling. Although the coupling is 
 too feeble to thermalize the ALP\, coherent forward scattering between the
  two sectors induces temperature-dependent mass shifts that substantially 
 modify both WIMP freeze-out and ALP misalignment dynamics\, giving rise to
  a novel coherent freeze-out mechanism. At high temperatures\, the WIMP th
 ermal bath spontaneously breaks the symmetry of the ALP potential\, displa
 cing the field to a new vacuum. The resulting back-reaction reduces the WI
 MP effective mass and significantly delays its freeze-out. Depending on th
 e strength of the coupling\, symmetry restoration occurs via either a firs
 t-order phase transition (FOPT) or a crossover. In the FOPT regime\, dark 
 matter consists solely of WIMPs\, whose delayed freeze-out permits annihil
 ation cross sections up to three orders of magnitude above the standard va
 lue\, while still yielding the correct relic density. In the crossover reg
 ime\, both WIMP and ALP can contribute to dark matter. Remarkably\, we fin
 d an "ALP miracle": a Planck-suppressed quadratic coupling yields an ALP a
 bundance comparable to the observed dark matter density\, largely independ
 ent of its initial displacement and mass.\n\nhttps://indico.itp.ac.cn/even
 t/416/contributions/2672/
LOCATION:Conference Center (2F) Front Area
URL:https://indico.itp.ac.cn/event/416/contributions/2672/
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