Neutrino Decay Into Fermionic Quasiparticles in Leptogenesis

Abstract

We calculate the decay rate of the lightest heavy Majorana neutrino in a thermal bath using finite temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rate differs from the usual approach by more than one order of magnitude in the temperature range which is interesting for the weak washout regime. This work summarizes the results of Ref. 1, to which we refer the interested reader.

The minimal scenario of leptogenesis

“…As it can be seen, the CP asymmetry parameter now includes finite density effects via a dependence on the Higgs and lepton distribution functions. This result agrees with that one found using thermal field theory in the real time formalism, when the right convention is used [92], as well as in the imaginary time formalism as recently obtained [96]. It, however, disagrees with an earlier work based on thermal field theory in the real time formalism, where a term quadratic in the distribution functions was found [29].…”

“…On the other hand, in the strong washout regime, K ≫ 1, the usual results from a vacuum calculation are recovered with a good accuracy. Recently, a new study came out using the imaginary time formalism [96], and the CP asymmetry parameter was found to differ from [29], and to agree with more recent attempts with non-equilibrium quantum field theory (see previous Section).…”

Systematic approach to leptogenesis in nonequilibrium QFT: Self-energy contribution to theCP-violating parameter

“…Using this, we find that the renormalized version of Eq. (22) can be obtained by replacinĝ G !Ĝ ren , as well asÅ 0 RðAÞ ðX; pÞ !Å 0 RðAÞ ðX; pÞ À Ẑ 0 p 2 þ ðM 2 Þ 0 . The latter prescription coincides with Eq.…”

“…In this approximation the possibly important medium effects are neglected from the very beginning. One can take them into account systematically by using the Schwinger-Keldysh/ Kadanoff-Baym formalism [9] or approximate selfconsistent equations derived from the Kadanoff-Baym equations (see [2,[10][11][12][13][14][15][16][17][18][19][20][21][22] for related work).…”

Thermal masses in leptogenesis

“…, whereas the decay in the light mode will be possible up to M N = m H (T ). The detailed shape of the decay rate including the two leptonic modes and its influence on the Boltzmann equations will be examined in a later work [13].…”