Speaker
Description
We study how a weakly mixed light scalar modifies a first-order electroweak phase transition supported by a heavier scalar in an extension of the Standard Model Higgs sector. Using a one-loop finite-temperature potential and multifield tunnelling calculations, we identify a regime in which the light scalar develops a large condensate in the metastable phase. Although this condensate barely changes across the critical bubble, it modifies the potential experienced by the Higgs and heavier singlet fields, delaying nucleation and increasing supercooling. Comparisons with a decoupled spectator benchmark show substantial changes in transition dynamics despite nearly identical critical temperatures. In representative benchmarks, delayed percolation occurs closer to a minimum of the tunnelling action $S_3/T$, reducing $\beta / H$ and enhancing the gravitational-wave amplitude.