Quantum leptogenesis I

Abstract

Thermal leptogenesis explains the observed matter-antimatter asymmetry of the universe in terms of neutrino masses, consistent with neutrino oscillation experiments. We present a full quantum mechanical calculation of the generated lepton asymmetry based on Kadanoff-Baym equations. Origin of the asymmetry is the departure from equilibrium of the statistical propagator of the heavy Majorana neutrino, together with CP violating couplings. The lepton asymmetry is calculated directly in terms of Green's functions without referring to "number densities". Compared to Boltzmann and quantum Boltzmann equations, the crucial difference are memory effects, rapid oscillations much faster than the heavy neutrino equilibration time. These oscillations strongly suppress the generated lepton asymmetry, unless the standard model gauge interactions, which cause thermal damping, are properly taken into account. We find that these damping effects essentially compensate the enhancement due to quantum statistical factors, so that finally the conventional Boltzmann equations again provide rather accurate predictions for the lepton asymmetry.

A White Paper on keV sterile neutrino Dark Matter

“…One possible starting point for this is the SchwingerKeldysh formalism of non-equilibrium quantum field theory [694][695][696][697], in which all properties of the system can be expressed in terms of correlation functions of the quantum fields, without reference to particles or asymptotic states. This framework allows for a first principles description of sterile neutrinos in a dense plasma, and significant progress has been made towards this goal [401,685,[698][699][700][701][702][703][704][705][706][707][708][709][710][711][712][713][714], in particular in the context of leptogenesis. However, even though exact equations can be written down, it remains a challenge to develop a systematic approximation scheme for their practical solution.…”

Langevin description of nonequilibrium quantum fields

“…An important byproduct of such investigations is that it allows one to bridge the gap between relatively simple situations where direct calculations from the basic equations of quantum field theory (QFT) can be done and more intricate cases, such as, for instance, situations with expanding and/or inhomogeneous backgrounds [6][7][8][9], or situations involving many types of fields and interactions such as lepto/baryo-genesis scenarios [8][9][10][11][12][13], where such calculations are difficult and where one often has to rely on effective descriptions. The most popular such effective approaches are kinetic descriptions [8,9,[12][13][14][15][16][17][18][19][20], or effective Langevin descriptions [21][22][23][24][25][26][27][28].…”

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

“…Several investigations of the lepton-number asymmetry have been carried out either within the Boltzmann rate equations and their quantum version known as Kadanoff-Baym equations [22][23][24][25]. Thermal effects are typically accounted for by including thermal masses and thermal distributions for the Higgs bosons and leptons appearing as decay products of heavy Majorana neutrinos.…”

“…The present study complements an analogous recent study [19] for the case of two heavy Majorana neutrinos with nearly degenerate masses relevant for resonant leptogenesis. Thermal corrections at zeroth order in SM couplings of the type given in [22][23][24] are exponentially suppressed in the non-relativistic regime and, therefore, not accounted for by an expansion in T /M 1 . Nevertheless, as discussed in appendix C of [19], one could easily retain the leading exponentially suppressed terms by a suitable modification of the calculation.…”