Abstract
We perform the first numerical calculation of the interplay between thermal and black hole induced leptogenesis, demonstrating that the right-handed neutrino surplus produced during the evaporation only partially mitigates the entropy dilution suffered by the thermal component. As such, the intermediate-mass regime of the right-handed neutrinos, $10^6{\rm~GeV} \lesssim M_{N} \lesssim 10^{9}{\rm~GeV}$, could not explain the observed baryon asymmetry even for fine-tuned scenarios if there existed a primordial black hole dominated era, consistent with initial black hole masses of $M_i \gtrsim \mathcal{O}\left(1\right)$ kg. Detection of the gravitational waves emitted from the same primordial black holes would place intermediate-scale thermal leptogenesis under tension.
Highlights
Primordial black holes (PBHs) could have been formed after the big bang through many different mechanisms [1,2,3]
We show that the baryon asymmetry undergoes a dilution due to the entropy injection from the black hole evaporation
We find that for the points in the model parameter space we explore, leptogenesis occurs in the strong washout regime where it has been shown that momentum averaged Boltzmann equations yields a near-identical lepton asymmetry compared to the full treatment [51]
Summary
Primordial black holes (PBHs) could have been formed after the big bang through many different mechanisms [1,2,3]. Hawking’s seminal papers [4,5] led to his discovery that black holes evaporate over time The fate of these PBHs is unknown: it is possible they disappear or leave a relic which can constitute a portion of dark matter [6,7,8,9,10,11,12]. We show that the baryon asymmetry undergoes a dilution due to the entropy injection from the black hole evaporation We quantify such depletion in the intermediate-scale regime, 106 ≲ MNðGeVÞ ≲ 109, and find that even for the most optimistic scenarios in this regime, the baryon asymmetry would be insufficient to explain the observed value for initial PBH masses Mi ≳ Oð1Þ kg and PBH energy density fractions to the total density at formation β0 ≳ 10−6.
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