Resonantly-Enhanced Baryogenesis through Asymmetric Capture by Primordial Black Holes
Primordial black holes (PBHs) can generate the Baryon Asymmetry of the Universe (BAU) through asymmetric capture of baryon-charge-carrying particles, but previous realizations of this mechanism typically yield an asymmetry well below the observed value because the relevant CP-violating scattering asymmetry is loop suppressed. We show that this limitation can be overcome through resonant CP violation in a mixed system of two nearly degenerate unstable fermions, $Y_{1,2}$, whose mass splitting is comparable to their decay widths. Rare production of the coherent $Y_1$--$Y_2$ state, followed by CP-asymmetric return and loss decays, generates an $\mathcal{O}(0.1)$ difference in integrated decay probabilities while preserving the global baryon charge at the Lagrangian level. Embedding this resonant source in the PBH-capture transport system yields the observed baryon asymmetry. We first reproduce the mechanism in a zero-temperature, sudden-evaporation treatment, which gives $η_B^{T=0}\simeq2.37\times10^{-10}\simeq2.72 η_B^{\rm obs}$. We find that after including thermal corrections and continuous PBH evaporation and entropy production, the resulting BAU becomes $η_B = 8.72\times 10^{-11}$ in agreement with the observed value. An interesting finding of the model is that even if PBH absorption remains active, we would still have BAU $η_{B}^{\text{no evap}} \sim 9.1 \times 10^{-12} \sim 0.105 η_B^{\rm obs}$. We further investigate gravitational-wave signatures associated with the primordial fluctuations responsible for PBH formation. The corresponding scalar-induced gravitational-wave spectra peak at $f \sim 0.16\text{--}0.17~\mathrm{MHz}$, with $h^2Ω_{\rm GW}^{\rm peak} \sim (3\text{--}7)\times 10^{-8}$. Under idealized sensitivity assumptions, U-DECIGO can achieve signal-to-noise ratios above 10 for the benchmark spectra.