On Higgs and sphaleron effects during the leptogenesis era

Abstract

We discuss the effects of various processes that can be active during the leptogenesis era, and present the Boltzmann equations that take them into account appropriately. A non-vanishing Higgs number asymmetry is always present, enhancing the washout of the lepton asymmetry. This is the main new effect when leptogenesis takes place at T > 10 12 GeV, reducing the final baryon asymmetry and tightening the leptogenesis bound on the neutrino masses. If leptogenesis occurs at lower temperatures, electroweak sphalerons partially transfer the lepton asymmetry to a baryonic one, while Yukawa interactions and QCD sphalerons partially transfer the asymmetries of the left-handed fields to the right-handed ones, suppressing the washout processes. Depending on the specific temperature range in which leptogenesis occurs, the final baryon asymmetry can be enhanced or suppressed by factors of order 20%-40% with respect to the case when these effects are altogether ignored.

Implications of flavor dynamics for fermion triplet leptogenesis

“…3. Considering only triplet annihilations (mediated by SM gauge bosons), decays (induced by the Yukawa couplings λ λ λ) and ∆L = 2 scatterings at O(λ 2 ), assuming a vanishing Higgs number asymmetry [12], can be written as…”

“…In the standard approach, in which light neutrinos acquire Majorana masses via the type I see-saw model [5], leptogenesis takes place via the CP violating out-of-equilibrium decays of heavy standard model fermionic singlets [6]. This scenario for leptogenesis has been widely discussed in the literature [7] and indeed a lot of progress in the understanding of the generation of the lepton asymmetry within this scenario has been achieved [8,9,10,11,12,13,14,15].…”

Leptogenesis in $E_6 \times U(1)_A$ SUSY GUT model

“…On the other hand, for M 1 /M 0 1 40, the evolutions of the asymmetries of all lepton flavor are in the weak washout regime, and hence total lepton asymmetry is determined by only the asymmetry production by the CP asymmetric decay. Due to the additional washout contributions, in the parameter region, the final lepton asymmetry can be smaller than that the case without the flavor effects [19,20].…”

CP asymmetry in heavy Majorana neutrino decays at finite temperature: the hierarchical case

“…temperatures of the order of 10 9 GeV [26,27], whereas the unflavoured regime is found to be an appropriate choice only at very high temperatures, in particular T 10 12 GeV. In the flavoured case it makes sense to define a CP asymmetry for each lepton flavour; the CP asymmetry generated by the lightest Majorana neutrino decaying into leptons and anti-leptons of flavour f reads ǫ f = Γ(ν R,1 → ℓ f + X) − Γ(ν R,1 →l f + X) f Γ(ν R,1 → ℓ f + X) + Γ(ν R,1 →l f + X) .…”