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.

  • $\begingroup$ 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. $\endgroup$
    – gj255
    Jul 7, 2017 at 20:40
  • $\begingroup$ @gj255 Yes, that's what I was getting at when I mentioned the possibility of phase coexistence. $\endgroup$
    – tparker
    Jul 8, 2017 at 0:32
  • $\begingroup$ @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. $\endgroup$
    – SRS
    Aug 7, 2017 at 14:54
  • $\begingroup$ @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. $\endgroup$
    – tparker
    Aug 7, 2017 at 18:15

1 Answer 1


This has been sitting without an answer for some years, so I will describe how I see this cosmological phase transition.

I see it as similar to any phase transition: when water boils does it start with the whole mass of water? No, there are regions where the transition has happened and regions where it has not. The basic reason is that temperature is a statistical variable. For a process that needs a specific temperature to happen it means that statistically on the average that temperature is reached, but there will be tails where not the whole mass will have the same statistical distribution , some time must pass for the whole volume of water to come to 100C.

So I see the cosmological transition in the same way, some regions will have the necessary Temperature ( kinetic energy low enough to break the symmetry) and some not. I have explored this in an answer here, in a simpler format,not cosmological, by looking at the phase diagram where plasma is shown. Energy density is important and it will be different for different regions,imo, at the beginning of the transition.

I am trying unsuccessfully to find a phenomenologist in the Alice experiment, where they claim quark gluon plasma, to see whether in their fit to the data they have taken into account that due to temperature being a statistical variable,the decay numbers behavior of the various weakly decaying particles will be different for different energy density regions. i.e. statistically some events will be at a higher temperature region, and this means that those events have not broken electroweak symmetry so there there should be the same numbers of top to mu. When these acquire mass as their region reaches the electroweak breaking scale, the number of tops would be much larger than in low energy interactions. This might be detectable with a suitable experiment.

Cosmologically, this would mean that there would be an equal number of tops to muons created before symmetry breaking , and the numbers would change drastically after.( I don't see an easy experiment to check this)


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