Resonant Leptogenesis

TL;DR

This paper demonstrates that baryogenesis via resonant leptogenesis can be realized with TeV-scale heavy Majorana neutrinos while remaining consistent with solar and atmospheric neutrino data. It develops a robust field-theoretic framework that combines RIS subtraction with a resummation of unstable-particle mixing to obtain finite, gauge-invariant CP asymmetries, and couples these to a comprehensive Boltzmann-equation network that includes gauge-mediated scatterings. The authors show that resonant enhancement allows sizable CP violation and efficient lepton-number generation even for large out-of-equilibrium parameters, and that the resulting BAU can match observations for realistic neutrino textures and phases. The work provides a versatile framework applicable to broad leptogenesis scenarios and highlights phenomenological implications for LFV and collider searches at the TeV scale.

Abstract

We study the scenario of thermal leptogenesis in which the leptonic asymmetries are resonantly enhanced through the mixing of nearly degenerate heavy Majorana neutrinos that have mass differences comparable to their decay widths. Field-theoretic issues arising from the proper subtraction of real intermediate states from the lepton-number-violating scattering processes are addressed in connection with an earlier developed resummation approach to unstable particle mixing in decay amplitudes. The pertinent Boltzmann equations are numerically solved after the enhanced heavy-neutrino self-energy effects on scatterings and the dominant gauge-mediated collision terms are included. We show that resonant leptogenesis can be realized with heavy Majorana neutrinos even as light as about 1 TeV, in complete accordance with the current solar and atmospheric neutrino data.

Figures (9)

• Figure 1: Feynman diagrams contributing to the $L$-violating decays of heavy Majorana neutrinos, $N_i \to L^C \Phi^\dagger$, where $L$ and $\Phi$ represent lepton and Higgs-boson iso-doublets, respectively: (a) tree-level graph, and one-loop (b) self-energy and (c) vertex graphs.
• Figure 2: Resummed diagrams contributing to the resonant part of the $2\to 2$ scattering amplitude of the process $L\Phi \to L^C\Phi^\dagger$. Depending on the context, $L,\ N_{1,2}$ may denote scalar or fermion particles (see also text).
• Figure 3: $\varepsilon$- and $\varepsilon'$-types of CP violation in the decays of heavy Majorana neutrinos.
• Figure 4: Numerical estimates of $\eta_L$, $\eta_{N_{1,2}}$ as functions of $z = m_{N_1}/T$, for a model where $m_{N_1}=1$ TeV, $x_N = \frac{m_{N_2}}{m_{N_1}}-1= 7.7\times 10^{-10}$, $\varepsilon = 4.3\times10^{-7}$, $\bar{\varepsilon}= -i\,4.3\times10^{-7}$, and for (a)$\eta^{\,\mathrm{in}}_{L}=0$ and (b)$\eta^{\,\mathrm{in}}_{L}=1$. The horizontal dotted line shows the value of $\eta_L$ needed to produce the observed $\eta_B$. The vertical dotted line corresponds to $T = T_c = 200$ GeV. "Improved" and "partial" refer to whether or not the CP-violating scattering terms proportional to $\delta_{N_i}\left(\Gamma^{S\;(i)}_{\rm Yukawa} + \Gamma^{S\;(i)}_{\rm Gauge}\right)$ are included in the BE (\ref{['BEL']}).
• Figure 5: Numerical estimates of $\eta_L$, $\eta_{N_{1,2}}$ as functions of $z = m_{N_1}/T$, for two scenarios with $m_{N_1}=1$ TeV, $x_N = \frac{m_{N_2}}{m_{N_1}} - 1 = \varepsilon^2$ and $\eta^{\rm in}_L = 0$, $\eta^{\rm in}_{N_{1,2}} = 1$: (a)$\bar{\varepsilon} = e^{i\theta} \varepsilon$ and $\varepsilon = 4.3\times10^{-7}$; (b)$\bar{\varepsilon} = i\xi \varepsilon$ and $|\varepsilon \bar{\varepsilon}| = 1.85 \times10^{-13}$. The meaning of the horizontal and vertical dotted lines is the same as in Fig. \ref{['fig:num1']}.