# What did electroweak symmetry breaking actually look like?

Approximately one picosecond after the Big Bang, the universe cooled down enough to pass through the electroweak phase transition. At this point the Higgs mechanism kicked in, the weak force became short-ranged and observationally distinct from electromagnetism, particles gained mass, the electroweak era ended, and the quark era began (and lasted one whole microsecond!).

I'm sure that this is gigantic subject, but could anyone explain in just a few sentences what the actual dynamical process of symmetry breaking looked like as the universe passed through the critical temperature? What would you have observed right at the critical moment? A sudden shower of Higgs bosons appearing out of nowhere?

As I understand it, the transition is believed to have been weakly first-order, and the fields are believed to have equilibrated fast enough that it was effectively adiabatic, despite only lasting a fraction of a picosecond. Were the spatial temperature fluctuations strong enough that there was a moment of phase coexistence, with particles having mass in some parts of the universe but not others? How would that work? (You wouldn't have sharp domain walls between regions where the Higgs field had different values though, because the broken symmetry is continuous.)

Note that I'm asking about the phenomenology of actual dynamical symmetry breaking, not the phenomenology of broken symmetry.

• Aside: the fact that the symmetry is continuous might imply that domain walls aren't topologically protected, but nevertheless domain walls might exist out of equilibrium, for instance if the phase transition proceeded by nucleation of 'bubbles' of the new stable phase in a background of the old phase. – gj255 Jul 7 '17 at 20:40
• @gj255 Yes, that's what I was getting at when I mentioned the possibility of phase coexistence. – tparker Jul 8 '17 at 0:32
• @tparker "A sudden shower of Higgs bosons appearing out of nowhere?"-It's not true that the Higgs boson gives mass to the $W$ and Z bosons. It is the non-zero vacuum expectation value (VEV) of the Higgs field that gives mass to the SU(2) gauge bosons and triggers SSB. – SRS Aug 7 '17 at 14:54
• @SRS Right. I wasn't implying that the newly appeared Higgs bosons would give the $W$ and $Z$ bosons masses. I was implying that the Higgs field's sudden acquisition of a nonzero VEV would lead to both a shower of Higgs bosons and, separately, the $W$ and $Z$ bosons' gaining mass. – tparker Aug 7 '17 at 18:15