Primordial black holes from a cosmic phase transition: The collapse of Fermi-balls

Kiyoharu Kawana,Ke-Pan Xie

doi:10.1016/j.physletb.2021.136791

Kiyoharu Kawana, Ke-Pan Xie

Open Access

https://doi.org/10.1016/j.physletb.2021.136791

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Abstract

We propose a novel primordial black hole (PBH) formation mechanism based on a first-order phase transition (FOPT). If a fermion species gains a huge mass in the true vacuum, the corresponding particles get trapped in the false vacuum as they do not have sufficient energy to penetrate the bubble wall. After the FOPT, the fermions are compressed into the false vacuum remnants to form non-topological solitons called Fermi-balls, and then collapse to PBHs due to the Yukawa attractive force. We derive the PBH mass and abundance, showing that for a O(GeV) FOPT the PBHs could be ∼1017 g and explain all of dark matter. If the FOPT happens at higher scale, PBHs are typically overproduced and extra dilution mechanism is necessary to satisfy current constraints.

Highlights

Primordial black holes (PBHs) are hypothetical black holes which form prior to any galaxies and stars [1, 2]
Not yet confirmed by experiments, PBHs have been a source of interest, as they can serve as a good candidate for dark matter (DM) [2,3,4,5,6,7,8], can seed supermassive black holes [9,10,11,12,13], can generate the baryon asymmetry of the Universe [14,15,16,17,18,19,20,21,22,23,24], and can explain some gravitational wave (GW) signals at LIGO/Virgo [25,26,27,28,29,30], etc
We have discussed a novel PBH formation mechanism based on the collapse of Fermi-balls from a first-order phase transition (FOPT) and illustrated that it can explain all of DM if T∗ 100 GeV

Summary

INTRODUCTION

Primordial black holes (PBHs) are hypothetical black holes which form prior to any galaxies and stars [1, 2]. After the FOPT, fermions are trapped in the old (false) vacuum and compressed to form non-topological solitons called Fermi-balls [54] if there is an asymmetry between the number densities of χ and χ, such that only χ’s survive the χχ → φφ annihilation. The conditions for Fermi-ball formation can be satisfied in many new physics models [54]: gχw∗ T∗ can be realized by a supercooled FOPT [55,56,57,58,59,60,61] or strong coupling [62, 63] while the χ asymmetry can be generated by various asymmetric DM mechanisms [64,65,66]. Inside the Fermi-ball is the false vacuum φ = 0, in which χ’s are massless fermions interacting with each other via the attractive Yukawa potential.

FERMI-BALL FORMATION IN FOPT

COLLAPSE OF FERMI-BALLS INTO PBHS

THE PBH PROFILE

SUMMARY