Speaker
Description
A first-order phase transition (FOPT) remains a possible source of the stochastic gravitational-wave (GW) background observed by pulsar timing arrays (PTAs). Can independent observations help test this interpretation? In this talk, I will show that an FOPT capable of generating the observed GW background also produces enhanced curvature perturbations over a narrow range of scales, leading to the formation of ultra-compact minihalos (UCMHs). These minihalos could alter the gravitational lensing magnification of the MACS J1149 LS1 “Icarus” caustic-crossing event. By using the observed magnification to constrain the UCMH abundance, we can derive an upper bound on the curvature perturbations associated with the FOPT and test whether the transition can consistently explain the PTA signal.