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  • Open Access

Leptogenesis in the presence of density perturbations

Kenta Hotokezaka1,*, Ryusuke Jinno2,†, and Rin Takada1,‡

  • 1Research Center for the Early Universe (RESCEU), Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 2Department of Physics, Graduate School of Science, Kobe University, 1-1 Rokkodai, Kobe, Hyogo 657-8501, Japan

  • *Contact author: kentah@resceu.s.u-tokyo.ac.jp
  • †Contact author: jinno@phys.sci.kobe-u.ac.jp
  • ‡Contact author: takada-rin@resceu.s.u-tokyo.ac.jp
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Phys. Rev. D 111, 115029 – Published 25 June, 2025

DOI: https://doi.org/10.1103/s7dp-8f59

Abstract

We point out a new effect on the freeze-out process of heavy particles induced by density perturbations in the early Universe, which we call “acoustically driven freeze-out.” This beyond-linear effect is caused by the exponential decoupling of heavy particles from the thermal bath in the presence of density perturbations, and already at moderately large values δT/T¯=O(10−2), it cannot be captured by linear perturbation theory. We illustrate this effect with leptogenesis taking the decay and inverse decay of heavy neutrinos into account and discuss its phenomenological implications. We found that perturbations always enhance the (spatially averaged) values of the final lepton asymmetry, and as a result, constraints on the mass of heavy neutrinos are found to be relaxed in the presence of perturbations.

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Phys. Rev. D 111, 115029– Published 25 June, 2025
  • Received 28 January 2025
  • Accepted 20 May 2025
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