Abstract
The origin of the baryon asymmetry of the Universe (BAU) and the nature of dark matter are two of the most challenging problems in cosmology. We propose a scenario in which the gravitational collapse of large inhomogeneities at the quark-hadron epoch generates both the baryon asymmetry and most of the dark matter in the form of primordial black holes (PBHs). This is due to the sudden drop in radiation pressure during the transition from a quark-gluon plasma to non-relativistic hadrons. The collapse to a PBH is induced by fluctuations of a light spectator scalar field in rare regions and is accompanied by the violent expulsion of surrounding material, which might be regarded as a sort of “primordial supernova". The acceleration of protons to relativistic speeds provides the ingredients for efficient baryogenesis around the collapsing regions and its subsequent propagation to the rest of the Universe. This scenario naturally explains why the observed BAU is of order the PBH collapse fraction and why the baryons and dark matter have comparable densities. The predicted PBH mass distribution ranges from subsolar to several hundred solar masses. This is compatible with current observational constraints and could explain the rate, mass and low spin of the black hole mergers detected by LIGO-Virgo. Future observations will soon be able to test this scenario.
Highlights
The LIGO-Virgo detections [1,2,3,4] of gravitational waves from the coalescence of massive black holes has triggered renewed interest in primordial black holes (PBHs) as dark matter (DM) [5,6,7]
MPBH is of order the Chandrasekhar mass, MCh ≈ 1.4 M, for PBHs forming at the Quantum Chromodynamics (QCD) scale, ΛQCD ≈ 200 MeV
The production of the baryon asymmetry of the Universe (BAU) through CP-violating processes is one example of this, the usual assumption being that new high-energy physics generates the baryon asymmetry everywhere simultaneously via out-of-equilibrium particle decays or first-order phase transitions
Summary
The LIGO-Virgo detections [1,2,3,4] of gravitational waves from the coalescence of massive black holes has triggered renewed interest in primordial black holes (PBHs) as dark matter (DM) [5,6,7]. The sudden gravitational collapse of the mass within the Hubble horizon at the QCD epoch releases a large amount of entropy and generates a relativistically expanding shockwave, with an effective temperature well above that of the surrounding plasma. Such high density hot spots might be regarded as primordial supernovae and provide the out-ofequilibrium conditions required to generate a baryon asymmetry through the well-known electroweak sphaleron transitions responsible for Higgs windings around the electroweak (EW) vacuum [14]. We mainly focus on the generation of the baryon asymmetry
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