High-Temperature Electroweak Symmetry Non-Restoration from New Fermions and Implications for Baryogenesis

Understand

The strength of electroweak symmetry breaking may substantially differ in the early Universe compared to the present day value.

• In the Standard Model, the Higgs vacuum expectation value (vev) vanishes and electroweak symmetry gets restored at temperatures above $\sim 160$ GeV due to the Higgs field interactions with the high-temperature plasma.
• It was however shown that new light singlet scalar fields may change this behaviour.
• The key feature is the non-standard dependence on the Higgs vev of the new particles mass which can vanish at large Higgs vev, inducing a negative correction to the Higgs thermal mass, leading to electroweak symmetry non-restoration at high temperature.