Wash-Out in N_2-dominated leptogenesis

We study the wash-out of a cosmological baryon asymmetry produced via leptogenesis by subsequent interactions. Therefore we focus on a scenario in which a lepton asymmetry is established in the out-of-equilibrium decays of the next-to-lightest right-handed neutrino. We apply the full classical Boltzmann equations without the assumption of kinetic equilibrium and including all quantum statistical factors to calculate the wash-out of the lepton asymmetry by interactions of the lightest right-handed state. We include scattering processes with top quarks in our analysis. This is of particular interest since the wash-out is enhanced by scatterings and the use of mode equations with quantum statistical distribution functions. In this way we provide a restriction on the parameter space for this scenarios.Comment: 26 pages, 4 figures, profound revision, exposition is now in flavor notation, one plot and discussion added, numerical error corrected, three plots changed, text polished, main results remain unchanged, reference added,matches published versio

Non-relativistic leptogenesis

Bödeker D, Wörmann M. Non-relativistic leptogenesis. Journal of Cosmology and Astroparticle Physics. 2014;2014(02):016.In many phenomenologically interesting models of thermal leptogenesis the heavy neutrinos are non-relativistic when they decay and produce the baryon asymmetry of the Universe. We propose a non-relativistic approximation for the corresponding rate equations in the non-resonant case, and a systematic way for computing relativistic corrections. We determine the leading order coefficients in these equations, and the first relativistic corrections. The non-relativistic approximation works remarkably well. It appears to be consistent with results obtained using a Boltzmann equation taking into account the momentum distribution of the heavy neutrinos, while being much simpler. We also compute radiative corrections to some of the coefficients in the rate equations. Their effect is of order 1% in the regime favored by neutrino oscillation data. We obtain the correct leading order lepton number washout rate in this regime, which leads to large (~ 20%) effects compared to previous computations

Full Boltzmann equations for leptogenesis including scattering

We study the evolution of a cosmological baryon asymmetry produced via leptogenesis by means of the full classical Boltzmann equations, without the assumption of kinetic equilibrium and including all quantum statistical factors. Beginning with the full mode equations we derive the usual equations of motion for the right-handed neutrino number density and integrated lepton asymmetry, and show explicitly the impact of each assumption on these quantities. For the first time, we investigate also the effects of scattering of the right-handed neutrino with the top quark to leading order in the Yukawa couplings by means of the full Boltzmann equations. We find that in our full Boltzmann treatment the final lepton asymmetry can be suppressed by as much as a factor of 1.5 in the weak wash-out regime (K<1), compared to the usual integrated approach which assumes kinetic equilibrium and neglects quantum statistics. This suppression is in contrast with the enhancement seen in some previous studies that considered only decay and inverse decay of the right-handed neutrino. However, this suppression quickly decreases as we increase K. In the strong wash-out regime (K>1), the full Boltzmann treatment and the integrated approach give nearly identical final lepton asymmetries (within 10 % of each other at K>3). Finally, we show that the opposing effects of quantum statistics on decays/inverse decays and the scattering processes tend to reduce the net importance of scattering on leptogenesis in the full treatment compared to the integrated approach.Comment: 39 pages, 8 figures, typos corrected, replaced to match published versio

Thermal production of ultrarelativistic right-handed neutrinos: Complete leading-order results

The thermal production of relativistic right-handed Majorana neutrinos is of importance for models of thermal leptogenesis in the early Universe. Right-handed neutrinos can be produced both by 1 2 decay or inverse decay and by 2 -> 2 scattering processes. In a previous publication, we have studied the production via 1 2 (inverse) decay processes. There we have shown that multiple scattering mediated by soft gauge boson exchange also contributes to the production rate at leading order, and gives a strong enhancement. Here we complete the leading order calculation by adding 2 -> 2 scattering processes involving either electroweak gauge bosons or third-generation quarks. We find that processes with gauge interactions give the most important contributions. We also obtain a new sum rule for the Hard Thermal Loop resummed fermion propagator.Comment: 27 pages, 7 figures. Error in the matrix element for the (subdominant) subprocess with s-channel fermion exchange corrected. This changes the corresponding phase space integral and the constant c_V. Numerically it increases the total 2 -> 2 rate by about 2 percent and the complete rate by about 1 percent. The main results and conclusions are unaffecte

Effects of reheating on leptogenesis

We study the evolution of a cosmological baryon asymmetry in leptogenesis when the right-handed neutrinos are produced in inflaton decays. By performing a detailed numerical study over a broad range of inflaton-neutrino couplings we show that the resulting asymmetry can be larger by two orders of magnitude or more than in thermal leptogenesis, if the reheating temperature T_{RH} is of the same order as the right-handed neutrino mass M_1. Hence, the lower limit on the baryogenesis temperature obtained in thermal leptogenesis can be relaxed accordingly

On the full Boltzmann equations for Leptogenesis

We consider the full Boltzmann equations for standard and soft leptogenesis, instead of the usual integrated Boltzmann equations which assume kinetic equilibrium for all species. Decays and inverse decays may be inefficient for thermalising the heavy-(s)neutrino distribution function, leading to significant deviations from kinetic equilibrium. We analyse the impact of using the full kinetic equations in the case of a previously generated lepton asymmetry, and find that the washout of this initial asymmetry due to the interactions of the right-handed neutrino is larger than when calculated via the integrated equations. We also solve the full Boltzmann equations for soft leptogenesis, where the lepton asymmetry induced by the soft SUSY-breaking terms in sneutrino decays is a purely thermal effect, since at T=0 the asymmetry in leptons cancels the one in sleptons. In this case, we obtain that in the weak washout regime (K ~< 1) the final lepton asymmetry can change up to a factor four with respect to previous estimates.Comment: 34 pages, 6 figures, to be published in JCA

Examining leptogenesis with lepton flavor violation and the dark matter abundance

Within a supersymmetric (SUSY) type-I seesaw framework with flavor-blind universal boundary conditions, we study the consequences of requiring that the observed baryon asymmetry of the Universe be explained by either thermal or non-thermal leptogenesis. In the former case, we find that the parameter space is very constrained. In the bulk and stop-coannihilation regions of mSUGRA parameter space (that are consistent with the measured dark matter abundance), lepton flavor-violating (LFV) processes are accessible at MEG and future experiments. However, the very high reheat temperature of the Universe needed after inflation (of about 10^{12} GeV) leads to a severe gravitino problem, which disfavors either thermal leptogenesis or neutralino dark matter. Non-thermal leptogenesis in the preheating phase from SUSY flat directions relaxes the gravitino problem by lowering the required reheat temperature. The baryon asymmetry can then be explained while preserving neutralino dark matter, and for the bulk or stop-coannihilation regions LFV processes should be observed in current or future experiments.Comment: 20 pages, 5 figures, 1 tabl

Hard-Thermal-Loop Corrections in Leptogenesis II: Solving the Boltzmann Equations

We investigate hard-thermal-loop (HTL) corrections to the final lepton asymmetry in leptogenesis. To this end we solve the Boltzmann equations with HTL-corrected rates and CP asymmetries, which we calculated in paper I of this series. We pay special attention to the influence of the two leptonic quasiparticles that arise at non-zero temperature. We include only decays and inverse decays and allow for the lepton modes to be either decoupled from each other, or to be in chemical equilibrium by some strong interaction, simulating the interaction with gauge bosons. In two additional cases, we approximate the full HTL lepton propagators with zero-temperature propagators, where we replace the zero-temperature mass by the thermal mass of the leptons $m_\ell(T)$ or the asymptotic mass $\sqrt{2} \, m_\ell(T)$. We compare the final lepton asymmetries of the four thermal cases and the zero-temperature case for zero, thermal and dominant initial neutrino abundance. The final lepton asymmetries of the thermal cases differ considerably from the vacuum case and from each other in the weak washout regime for zero initial neutrino abundance and in the intermediate regime for dominant initial neutrino abundance. In the strong washout regime, the final lepton asymmetry can be enhanced by a factor of two in the case of strongly interacting lepton modes.Comment: 51 pages, 27 figure

Thermal production of relativistic Majorana neutrinos: Strong enhancement by multiple soft scattering

The production rate of heavy Majorana neutrinos is relevant for models of thermal leptogenesis in the early Universe. In the high temperature limit the production can proceed via the 1 2 (inverse) decays which are allowed by the thermal masses. We consider new production mechanisms which are obtained by including additional soft gauge interactions with the plasma. We show that an arbitrary number of such interactions gives leading order contributions, and we sum all of them. The rate turns out to be smooth in the region where the 1 2 processes are kinematically forbidden. At higher temperature it is enhanced by a factor 3 compared to the 1 2 rate.Comment: 26 pages, 8 figures; added references, added comments on 2 to 2 scattering processes, improved appearance of fig. 8, corrected typos; matches published versio

Supersymmetric Leptogenesis and the Gravitino Bound

Supersymmetric thermal leptogenesis with a hierarchical right-handed neutrino mass spectrum requires the mass of the lightest right-handed neutrino to be heavier than about 10^9 GeV. This is in conflict with the upper bound on the reheating temperature which is found by imposing that the gravitinos generated during the reheating stage after inflation do not jeopardize successful nucleosynthesis. In this paper we show that a solution to this tension is actually already incorporated in the framework, because of the presence of flat directions in the supersymmetric scalar potential. Massive right-handed neutrinos are efficiently produced non-thermally and the observed baryon asymmetry can be explained even for a reheating temperature respecting the gravitino bound if two conditions are satisfied: the initial value of the flat direction must be close to Planckian values and the phase-dependent terms in the flat direction potential are either vanishing or sufficiently small.Comment: 9 pages. References added, version for Physics Letters