What is the effect on leptogenesis in the standard model if the electroweak phase transition is (i) first order and (ii) second order?


In the Standard Model there is neither first nor second order electroweak phase transition (EWPT), but rather a crossover. To get a first order transition, additional particles are needed. There are many different theories (2HDM, Higgs portal, MSSM, ...) covering this topic.

Considering leptogenesis $\Delta L \neq 0$ we need a first order PT, since non-equilibrium is one of the Sakharov conditions required for leptogenesis. If these conditions are fulfilled, sphaleron processes violate lepton (or baryon) number by "jumping" from the symmetric $(\phi = 0)$ to the broken $(\phi=\phi_0)$ phase. I found this plot: (Never mind the numbers, in the case of EWPT the critical temperature $T_c \sim \mathcal{O}(100 GeV)$ )

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  • $\begingroup$ This looks like a first order transition to me, or am I misreading the plot? $\endgroup$ – Ryan Thorngren Apr 4 '19 at 13:16

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