Testing Super-Heavy Dark Matter from Primordial Black Holes with Gravitational Waves

Abstract

Ultra-light primordial black holes with masses M BH < 10 9 g evaporate before big-bang nucleosynthesis producing all matter fields, including dark matter, in particular super-heavy dark matter: M DM 10 10 GeV. If the dark matter gets its mass via U (1) symmetry-breaking, the phase transition that gives a mass to the dark matter also produces cosmic strings which radiate gravitational waves. Because the symmetry-breaking scale Λ CS is of the same order as M DM , the gravitational waves radiated by the cosmic strings have a large enough amplitude to be detectable across all frequencies accessible with current and planned experimental facilities. Moreover, an epoch of early primordial black hole domination introduces a unique spectral break in the gravitational wave spectrum whose frequency is related to the super-heavy dark matter mass. Hence, the features of a stochastic background of primordial gravitational waves could shed light on the primordial black hole origin of super-heavy dark matter. In this perspective, the recent finding of a stochastic common-spectrum process across many pulsars by two nano-frequency pulsar timing arrays would fix the dark matter mass to be 3 × 10 13 GeV M DM 10 14 GeV. The (non-)detection of a spectral break at 0.2 Hz f * 0.4 Hz would (exclude) substantiate this interpretation of the signal.

Bounds from multi-messenger astronomy on the Super Heavy Dark Matter

“…Below Gµ = 10 −7 lies the CMB limit for the cosmic string tension [129]. The relevant sensitivity curves of currfnt or future GW detectors, such as the Einstein Telescope (ET), Cosmic Explorer (CE), LISA [130], BBO [131] are reproduced from [67] using Eq. ( 12).…”

“…( 12). The light yellow region is the allowed parameter space assuming the PHB emission to SHDM scenario from [67]. The dark and light green bands denote the predicted turning-point frequencies computed assuming the 1σ and 2σ prediction on Gµ parameter taken from [132] obtained from the fits to the NANOGrav data [133] for the examined SHDM particle masses.…”

“…There are several scenarios of effective DM particles production at various stages of early Universe evolution. SHDM can be created gravitationally at the end of inflation [52][53][54]61], during preheating [63,64] and reheating [59, 65,66], and from the collisions of vacuum bubbles at phase transitions [55,64], or from emission [67] of the primordial black holes (PBHs) [see 57, for a review].…”

“…The discovery of gravitational waves (GWs) by LIGO and Virgo collaboration of black holes [96-100] and neutron stars [101,102] has opened up a new cosmic frontier for the SHDM search by examination of the stochastic GW background (SGWB) [103][104][105][106] in the multifrequency range [67].…”

“…In addition, from the relation of the GW spectrum break, f * , with the SHDM mass, following Ref. [67], we mapped potential probes and limits of the SHDM particles masses on the f * − M X parameter space in Sec. III.…”