Equilibration of right-handed electrons

Abstract

We study the equilibration of right-handed electrons in the symmetric phase of the Standard Model. Due to the smallness of the electron Yukawa coupling, it happens relatively late in the history of the Universe. We compute the equilibration rate at leading order in the Standard Model couplings, by including gauge interactions, the top Yukawa-and the Higgs self-interaction. The dominant contribution is due to 2 → 2 particle scattering, even though the rate of (inverse) Higgs decays is strongly enhanced by multiple soft scattering which is included by Landau-Pomeranchuk-Migdal (LPM) resummation. Our numerical result is substantially larger than approximations presented in previous literature. 1

Kinetic equations for sterile neutrinos from thermal fluctuations

“…Then it is convenient to include a kinetic equation for B [32,33], since B is not violated by the sterile-neutrino Yukawa interaction so that only the sphaleron rate enters this equation. When T ∼ 85 TeV, the lepton number carried by right-handed electrons evolves slowly, and one has to include the kinetic equation for L eR [28]. Using a different approach from ours, an equation similar to (3.38) was derived previously in [19], 12 assuming M i ≪ T for all Majorana masses, so that the condition (3.12) is satisfied.…”

“…Equation (5.3) is consistent with[19] and[28], where the Higgs chemical potential is defined as a particle chemical potential 29. See equation (5.7) of reference[37].…”

“…In the temperature range 8.5 · 10 4 GeV ≪ T ≪ 10 9 GeV the lepton number L eR carried by right-handed electrons is not yet efficiently violated by the electron Yukawa coupling [28] so that it constitutes an additional conserved charge, and we have to introduce a corresponding chemical potential in (3.36). The relation between all charges and their chemical potentials has been obtained in [28]. 21 Hypercharge neutrality implies 1) and the relation between L eR and its chemical potential reads…”

“…appears, rather than µ ϕ . 28 The relation between the hypercharge chemical potential µ Y and the chemical potentials of the slowly varying charges depends on the temperature, see section 4. The leading contribution from (5.2) is due to soft Higgs momenta, which are cut off by the thermal Higgs mass [43]…”

Sterile neutrino dark matter via GeV-scale leptogenesis?

“…(iv) Additional semi-conserved quantities such as chiral charges or helical magnetic fields have long been speculated to play a role in cosmology (cf., e.g., refs. [35][36][37][38][39][40]), and they could conceivably interfere with late-time lepton asymmetries as well.…”