Electroweak-Scale Resonant Leptogenesis

TL;DR

This work presents a minimal, electroweak-scale realization of resonant leptogenesis that leverages single-lepton flavour dynamics and sphaleron effects. By constructing a flavour-resolved Boltzmann framework and a nearly degenerate heavy Majorana neutrino sector with controlled symmetry breaking, the authors demonstrate robust generation of the baryon asymmetry with reduced sensitivity to initial conditions. The approach yields concrete, testable predictions: sizable $0\\nu\\beta\\beta$ decay with $|\\langle m \\rangle| \sim 0.013$ eV, measurable LFV signals such as $\\mu \\to e\\gamma$ and $\\mu \\to e$ conversion, and collider-accessible heavy neutrinos with appreciable couplings to $e$ and $\\mu$. These connections provide a tangible link between cosmology and upcoming experiments across low-energy precision tests and high-energy colliders.

Abstract

We study minimal scenarios of resonant leptogenesis near the electroweak phase transition. These models offer a number of testable phenomenological signatures for low-energy experiments and future high-energy colliders. Our study extends previous analyses of the relevant network of Boltzmann equations, consistently taking into account effects from out of equilibrium sphalerons and single lepton flavours. We show that the effects from single lepton flavours become very important in variants of resonant leptogenesis, where the observed baryon asymmetry in the Universe is created by lepton-to-baryon conversion of an individual lepton number, for example that of the tau lepton. The predictions of such resonant tau-leptogenesis models for the final baryon asymmetry are almost independent of the initial lepton-number and heavy neutrino abundances. These models accommodate the current neutrino data and have a number of testable phenomenological implications. They contain electroweak-scale heavy Majorana neutrinos with appreciable couplings to electrons and muons, which can be probed at future e+ e- and mu+ mu- high-energy colliders. In particular, resonant tau-leptogenesis models predict sizeable 0νββdecay, as well as e- and mu-number-violating processes, such as mu -> e gamma and mu -> e conversion in nuclei, with rates that are within reach of the experiments proposed by the MEG and MECO collaborations.

Figures (10)

• Figure 1: Finite radiative effects contributing to the light-neutrino mass matrix.
• Figure 2: The predicted evolution of $\eta_{L_l}$ and $\eta_B$, for models with $m_N =$ 100, 250, 500 and 1000 GeV, and $\eta_{N_{\alpha}}^{\mathrm{in}} = 1$. The model parameters are given in (\ref{['nupars1']}), (\ref{['nupars2']}), and Tables \ref{['mnu-params']} and \ref{['baryon-param']}. The horizontal grey dashed line shows the baryon asymmetry needed to agree with observational data.
• Figure 3: The (in)dependence of the final baryon asymmetry on the initial lepton, baryon and heavy Majorana neutrino abundances for (a) $m_N =$ 250 GeV and (b) $m_N =$ 100 GeV. The model parameters and the meaning of the horizontal grey line are the same as in Fig. \ref{['evolution-all']}.
• Figure 4: The complete independence of the final BAU on the initial lepton and baryon abundances for the $m_N = 500$ GeV scenario, with model parameters the same as in Fig. \ref{['evolution-all']}.
• Figure 5: The ratio of various collision terms to the Hubble parameter plotted for the $m_N = 250$ GeV scenario presented in Fig. \ref{['evolution-all']}.