Reconciling resonant leptogenesis and baryogenesis via neutrino oscillations

We derive non-equilibrium quantum transport equations for flavour-mixing fermions. We develop the formalism mostly in the context of resonant leptogenesis with two mixing Majorana fermions and one lepton flavour, but our master equations are valid more generally in homogeneous and isotropic systems. We give a hierarchy of quantum kinetic equations, valid at different approximations, that can accommodate helicity and arbitrary mass differences. In the mass-degenerate limit the equations take the familiar form of density matrix equations. We also derive the semiclassical Boltzmann limit of our equations, including the CP-violating source, whose regulator corresponds to the flavour coherence damping rate. Boltzmann equations are accurate and insensitive to the particular form of the regulator in the weakly resonant case ∆m » Γ, but for ∆m ≲ Γ they are qualitatively correct at best, and their accuracy crucially depends on the form of the CP-violating source.

Section: Jhep09(2021)119mentioning

confidence: 91%

Section: Jhep09(2021)119mentioning

confidence: 99%

Flavour mixing transport theory and resonant leptogenesis

Jukkala

Kainulainen

Rahkila

2021

“…In particular, it was found that the Majorana mass scale of right-handed neutrinos could be as low as the TeV, GeV or even MeV scale [7,[26][27][28][29][30]; for a recent overview see e.g. [31,32]. While two HNLs are sufficient to explain neutrino masses and oscillations as well as the origin of the matter-antimatter asymmetry, a third particle can play the role of dark matter [6-8, 33, 34] within the Neutrino Minimal Standard Model (νMSM).…”

Section: Heavy Neutral Leptonsmentioning

confidence: 99%

Reinterpreting the ATLAS bounds on heavy neutral leptons in a realistic neutrino oscillation model

Tastet

Ruchayskiy

Timiryasov

2021

Heavy neutral leptons (HNLs) are hypothetical particles, motivated in the first place by their ability to explain neutrino oscillations. Experimental searches for HNLs are typically conducted under the assumption of a single HNL mixing with a single neutrino flavor. However, the resulting exclusion limits may not directly constrain the corresponding mixing angles in realistic HNL models — those which can explain neutrino oscillations. The reinterpretation of the results of these experimental searches turns out to be a non-trivial task, that requires significant knowledge of the details of the experiment. In this work, we perform a reinterpretation of the latest ATLAS search for HNLs decaying promptly to a tri-lepton final state. We show that in a realistic model with two HNLs, the actual limits can vary by several orders of magnitude depending on the free parameters of the model. Marginalizing over the unknown model parameters leads to an exclusion limit on the total mixing angle which can be up to 3 orders of magnitude weaker than the limits reported in ref. [1]. This demonstrates that the reinterpretation of results from experimental searches is a necessary step to obtain meaningful limits on realistic models. We detail a few steps that can be taken by experimental collaborations in order to simplify the reuse of their results.

“…Both have been studied carefully and with different formalisms (see [4] and [5] for comprehensive reviews and references). In the last few years there have also been works addressing the case of neutrinos in the intermediate mass range of several tens to hundreds of GeV, which requires a careful implementation of the helicity degree of freedom in the transport equations [6][7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

CP violation in mixing and oscillations for leptogenesis. Part II. The highly degenerate case

Racker

2021

We extend to the highly degenerate case a recent approach for analyzing the sources of CP violation in baryogenesis models with quasi-degenerate neutrinos. In this approach an expansion of the resummed propagator around the poles is plugged into a quantum field theory model of neutrino oscillations and a source term for the time evolution of the lepton asymmetry is built directly from the probabilities of lepton number violating processes involving only stable particles. This allows for a transparent consideration of unitarity requirements. The source term has contributions that can be identified with CP violation from mixing, oscillations and interference between both. For the highly degenerate case, i.e. when the mass difference between two neutrinos is similar or smaller than their decay widths, we find that in general the mixing and oscillation terms contribute with opposite signs to the generation of lepton asymmetry and the contribution of the interference term is typically very relevant and crucial to ensure unitarity is satisfied. Moreover, the expressions we obtain are finite in the double degenerate limit of equal masses and couplings. The calculations are done in a simple scalar toy model.