Beyond the Standard Model Explanations of GW190521
  The LIGO/Virgo collaboration has recently announced the detection of a heavy
binary black hole merger, with component masses that cannot be explained by
standard stellar structure theory. In this letter we propose several
explanations based on models of new physics, including new light particle
losses, modified gravity, large extra dimensions, and a small magnetic moment
of the neutrino. Each of these affect the physics of the pair-instability
differently, leading to novel mechanisms for forming black holes inside the
black hole mass gap.
