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

Abstract

The generation of a baryon asymmetry via leptogenesis is usually studied by means of classical kinetic equations whose applicability to processes in the hot and expanding early universe is questionable. The approximations implied by the state-of-the-art description can be tested in a first-principle approach based on nonequilibrium field theory techniques. Here, we apply the Schwinger-Keldysh/Kadanoff-Baym formalism to a simple toy model of leptogenesis. We find that, within the toy model, medium effects increase the vertex contribution to the CP -violating parameter. At high temperatures it is a few times larger than in vacuum and asymptotically reaches the vacuum value as the temperature decreases. Contrary to the results obtained earlier in the framework of thermal field theory, the corrections are only linear in the particle number densities. An important feature of the Kadanoff-Baym formalism is that it is free of the double-counting problem, i.e. no need for real intermediate state subtraction arises. In particular, this means that the structure of the equations automatically ensures that the asymmetry vanishes in equilibrium. These results give a first glimpse into a number of new and interesting effects that can be studied in the framework of nonequilibrium field theory.

Improving electro-weak fits with TeV-scale sterile neutrinos

“…Substituting the terms proportional to g µν of Π µν W W and Π µν ZZ into the definitions of the S, T, U parameters we obtain Eqs. (15), (18) and (19 …”

“…Therefore, to compute (15) one can simply drop the ǫ −1 terms in the expansion of the loop functions and evaluate the remaining integrals numerically or analytically. As indicated in (15), the T parameter is a sum of the SM and new contributions. The SM contribution can be obtained from (15) by setting the active neutrino masses to zero and taking into account that R = 0 and U is unitary in the SM:…”

“…As indicated in (15), the T parameter is a sum of the SM and new contributions. The SM contribution can be obtained from (15) by setting the active neutrino masses to zero and taking into account that R = 0 and U is unitary in the SM:…”

“…According to this scenario the lepton asymmetry which is produced by the heavy neutrinos * evgeny.akhmedov@mpi-hd.mpg.de † alexander.kartavtsev@mpp.mpg.de ‡ manfred.lindner@mpi-hd.mpg.de § lisa.michaels@mpi-hd.mpg.de ¶ juri.smirnov@mpi-hd.mpg.de is converted into the baryon asymmetry by anomalous electro-weak processes [8][9][10]. Depending on the values of the masses and couplings in (1) the generation of the asymmetry proceeds either through decays [11][12][13][14][15][16][17][18][19][20][21][22][23] or via oscillations of the heavy neutrinos [24]. The extension of the SM spectrum by sterile neutrino states may even provide a solution to the third problem, since sterile neutrinos are a perfect dark matter candidate (see e.g.…”

Quantum mechanics of leptogenesis

“…In order to obtain a better understanding of leptogenesis, many authors have upgraded the Boltzmann equations to the so-called quantum Boltzmann [49][50][51][52] or the full quantum Boltzmann equations [53][54][55][56][57][58] equations. In this scenario, many properties have been studied, for example in [59][60][61][62][63][64][65][66][67] flavour effects are taken into account.…”