Primordial black hole production during first-order phase transitions

Abstract

Primordial black holes (PBHs) produced in the early Universe have attracted wide interest for their ability to constitute dark matter and explain the compact binary coalescence. We propose a new mechanism of PBH production during first-order phase transitions (PTs) and find that PBHs are naturally produced during PTs model-independently. Because of the randomness of the quantum tunneling, there always exists some probability that the vacuum decay is postponed in a whole Hubble volume. Since the vacuum energy density remains constant while radiation is quickly redshifted in the expanding Universe, the postponed vacuum decay then results in overdense regions, which finally collapse into PBHs as indicated by numerical simulations. Utilizing this result one can obtain mutual predictions and constraints between PBHs and GWs from PTs. The predicted mass function of PBHs is nearly monochromatic. We investigate two typical cases and find that 1) PBHs from a PT constitute all dark matter and GWs peak at $1$Hz, 2) PBHs from a PT can explain the coalescence events observed by LIGO-Virgo collaboration, and meanwhile GWs can explain the common-spectrum process detected by NANOGrav collaboration.

Figures (2)

• Figure 1: The evolution of the false vacuum fraction $F(t)$ (upper) and each component of the energy density (lower) in case 1 (left) and case 2 (right). The energy density of each component is rescaled by the initial value $\rho(t_{i})$. The bule and orange lines denotes the conditions inside and outside the overdense regions. The dot-dashed line denotes the time of the first bubble nucleation $t_{n}$ inside the overdense region. The solid and dashed lines in the lower panel respectively depict the evolution of the energy density of the false vacuum and the radiation.
• Figure 2: The predicted GW energy spectra and PBH mass functions in each case. The sensitivity curves can be found in Ref. Schmitz:2020syl, including EPTA Lentati:2015qwp, PPTA Shannon:2015ect, NANOGrav Arzoumanian:2018saf, IPTA Hobbs:2009yy, SKA Carilli:2004nx, LISA Audley:2017drz Taiji Guo:2018npi, DECIGO Kawamura:2011zz, BBO phinney2004big, LIGO, Virgo and KAGRA ( LVK) TheLIGOScientific:2014jeaSomiya:2011np, CE Reitze:2019iox, ET Punturo:2010zz. The PBH constraints include EG$\gamma$Carr:2009jm, INTEGRAL DeRocco:2019fjqLaha:2019ssqDasgupta:2019cae, Subaru HSC Niikura:2017zjd, Kepler Griest:2013esa, OGLE Niikura:2019kqi, MACHO/EROS Allsman:2000kgTisserand:2006zx, SNe Zumalacarregui:2017qqd, Ly$\alpha$Murgia:2019duy, CMB Poulin:2017bwe and LIGO-Virgo collabration (LVC) Vaskonen:2019jpv.