Sphaleron freeze-in baryogenesis with gravitational waves from the QCD transition
(2025) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics — Vol. 869 (2025)
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- Abstract
- A large primordial lepton asymmetry can generate the observed baryon asymmetry of the Universe (BAU) through nonrestoration of electroweak symmetry at a high temperature, suppressing the sphaleron rate (“sphaleron freeze-in”). Such an asymmetry can lead to a first-order cosmic QCD transition with an observable gravitational wave (GW) signal. With next-to-leading order dimensional reduction and the exact 1-loop fluctuation determinant, we find the required lepton asymmetry to be an order of magnitude smaller than previous estimates. We apply a new and improved QCD equation of state reconciling the lattice and functional QCD results, to identify the range of lepton flavor asymmetries inducing a first-order cosmic QCD transition. Consistency with the observational constraints on the lepton asymmetries from the CMB and BBN requires an entropy dilution by a factor of <math altimg="si16.svg"><mrow><mi mathvariant="script">O</mi><mo>(</mo><mn>10</mn><mo>)</mo></mrow></math> for the correct BAU, while the first-order QCD transition can itself occur without the need for any entropy dilution. We show that the sphaleron freeze-in paradigm can potentially be probed by future GW experiments like <math altimg="si10.svg"><mi>μ</mi></math>Ares, if the bubble wall velocity of the QCD transition is large.
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Oldengott, I., & et al. (2025). Sphaleron freeze-in baryogenesis with gravitational waves from the QCD transition. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 869. https://doi.org/10.1016/j.physletb.2025.139849 (Original work published 2025)