Systematic analysis of baryogenesis in non-equilibrium quantum field theory
Zusammenfassung der Projektergebnisse
Today the observed universe almost entirely consists of matter, i.e. is baryonically asymmetric. A very attractive explanation of the observed asymmetry is provided by the baryogenesis via leptogenesis scenario. Many important aspects of leptogenesis have been extensively studied by a number of researchers. The state of the art calculations use the Boltzmann equation with the vacuum scattering terms to compute the baryon asymmetry of the universe. The applicability of this approximation in the hot and rapidly expanding early universe is questionable and should be verified using methods of non-equilibrium quantum field theory. These methods offer an opportunity to calculate corrections to the results of the canonical analysis based on the use of the Boltzmann equation. Furthermore, they enable us to find the range of the applicability of the canonical approach and discover a number of qualitatively new effects. Using these methods we find that the lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we have derived approximate analytical expressions for the generated asymmetry and compared them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We have also taken into account corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compared the approximate analytical result for the lepton asymmetry with numerical results. To establish a connection between the new and canonical results, starting from fundamental equations for correlators of the quantum fields we have described the steps necessary to obtain quantum kinetic equations for quasiparticles. These can easily be compared to conventional results and overcome conceptional problems inherent in the canonical approach. Beyond CP-violating decays we have included also those scattering processes which are tightly related to the decays in a consistent approximation of fourth order in the Yukawa couplings. It has been demonstrated explicitly how the S-matrix elements for the scattering processes in the conventional approach are related to two- and three-loop contributions to the effective action. We have also derived effective decay and scattering amplitudes taking medium corrections and thermal masses into account. In this context we also investigated CP-violating Higgs decay within the same formalism. From the kinetic equations we derive rate equations for the lepton asymmetry improved in that they include quantumstatistical effects and medium corrections to the quasiparticle properties. In addition we have also studied the contribution to leptogenesis from ∆L = 1 decay and scattering processes mediated by the Higgs with quarks in the initial and final states using the formalism of non-equilibrium quantum field theory. To compute the collision term we have taken into account one- and two-loop contributions to the lepton self-energy and used the extended quasiparticle approximation for the Higgs two-point function. The resulting CP-violating and washout reaction densities have been numerically compared to the conventional ones. Thus, the posed questions have been addressed and the intended research objectives successfully achieved.
Projektbezogene Publikationen (Auswahl)
- “Leptogenesis from first principles in the resonant regime”. Annals Phys. 328 (2013) 26-63
M. Garny, A. Kartavtsev, A. Hohenegger
(Siehe online unter https://doi.org/10.1016/j.aop.2012.10.007) - “Leptogenesis in models with keV sterile neutrino dark matter”. J. Phys. G: Nucl. Part. Phys. 40 (2013) 095202
F. Bezrukov, A. Kartavtsev, M. Lindner
(Siehe online unter https://doi.org/10.1088/0954-3899/40/9/095202) - “Systematic approach to thermal leptogenesis”. Phys.Rev. D87 (2013) 085009
T. Frossard, M. Garny, A. Hohenegger, A. Kartavtsev, D. Mitrouskas
(Siehe online unter https://doi.org/10.1103/PhysRevD.87.085009) - “Systematic approach to ∆L = 1 processes in thermal leptogenesis”. Phys. Rev. D 87 (2013) 125006
T. Frossard, A. Kartavtsev, D. Mitrouskas
(Siehe online unter https://doi.org/10.1103/PhysRevD.87.125006)
