Speaker
Description
A first-order electroweak phase transition in the CP-conserving type-I two-Higgs-doublet model can source a gravitational wave background in the LISA band. From extensive Monte Carlo scans over the collider-viable parameter space, we find that LISA-detectable signals arise almost exclusively where observable deviations at the HL-LHC are predicted, in particular in the H → ZZ channel for a heavy neutral CP-even scalar around 180-250 GeV. The converse fails: an audible signal requires so much tuning that a collider discovery would say little about LISA. I quantify the theoretical uncertainties behind these statements by comparing BSMPT and TransitionListener, and discuss realizations without high-temperature symmetry restoration, which combine the loudest gravitational wave signals with the weakest collider coverage.