Unrestored Electroweak Symmetry

Abstract

The commonly assumed cosmological history of our Universe is that at early times and high temperatures the Universe went through an electroweak phase transition (EWPT). Assuming an EWPT, and depending on its strength, there are many implications for baryogenesis, gravitational waves, and the evolution of the Universe in general. However, it is not true that all spontaneously broken symmetries at zero temperature are restored at high temperature. In particular the idea of "inverse symmetry breaking" has long been established in scalar theories with evidence from both perturbative and lattice calculations. In this Letter we demonstrate that with a simple extension of the standard model it is possible that the EW symmetry was always broken or only temporarily passed through a symmetry-restored phase. These novel phase histories have many cosmological and collider implications that we discuss. The model presented here serves as a useful benchmark comparison for future attempts to discern the phase of our Universe at T≥a few GeV.