Missing in Action: New Physics and the Black Hole Mass Gap

Abstract

We demonstrate the power of the black hole mass gap as a novel probe of fundamental physics. New light particles that couple to the Standard Model can act as an additional source of energy loss in the cores of population-III stars, dramatically altering their evolution. We investigate the effects of two paradigmatic weakly coupled, low-mass particles, axions and hidden photons, and find that the pulsational pair instability, which causes a substantial amount of mass loss, is suppressed. As a result, it is possible to form black holes of 72M or heavier, deep inside the black hole mass gap predicted by the Standard Model. The upper edge of the mass gap is raised to > 130M , implying that heavier black holes, anticipated to be observed after LIGO's sensitivity is upgraded, would also be impacted. In contrast, thermally produced heavy particles would remain in the core, leading to the tantalizing possibility that they drive a new instability akin to the electron-positron pair instability. We investigate this effect analytically and find that stars that avoid the electronpositron pair instability could experience this new instability. We discuss our results in light of current and upcoming gravitational wave interferometer detections of binary black hole mergers.

Evidence for hierarchical black hole mergers in the second LIGO--Virgo gravitational-wave catalog

“…It is necessary to consider this hierarchical merger channel when using catalogs of GW sources to make inferences about the physics of black hole formation. For example, inference of the location of the lower edge of the pair-instability mass gap, which could potentially constrain nuclear reaction rates (Farmer et al 2020) or beyond Standard Model physics (Croon et al 2020;Straight et al 2020), using detections of black holes in the 50M regime would be contaminated by the presence of 2G black holes. In order to distinguish between 1G and 2G black holes, we must account simultaneously for the shapes of 1G and 2G populations and the relative frequencies of hierarchical mergers.…”

Hierarchical mergers of stellar-mass black holes and their gravitational-wave signatures

“…Several alternative explanations for the occurrence of GW190521 have also been put forward, ranging from critically assessing uncertainties in the lower edge of the mass gap, 47,53,228,229 Population III stars at very low-metallicity, 53,54,230 accretion onto either stellar-origin 58,59,213 or primordial 231,232 BHs, and stellar mergers. 37,55,56 Additional speculations include invoking beyond-standard-model physics 233,234 exotic compact objects, 235,236 and dark-matter annihilation. 237 From a dataanalysis perspective alone, there is also the concrete possibility that the primary and secondary components of GW190521 are actually above and below the pair instability gap respectively, and no object is inside it.…”

Anomaly-free leptophilic axionlike particle and its flavor violating tests

“…Recently, the Xenon collaboration reported the observation of an excess in the electron recoiling energy around the keV scale in the Xenon1T detector [1]. Shortly after its announcement, a lot of theoretical work has been done to interpret the results in the context of axion-like particles (ALPs) [2][3][4][5][6][7][8][9][10], dark matter , neutrinos [36][37][38][39][40][41][42][43][44][45] and solar axions [46][47][48], which, however, are subject to stringent constraints from stellar cooling [49][50][51]. In this work we focus on the ALP framework.…”