Lepton asymmetry from mixing and oscillations

TL;DR

This paper clarifies how CP-asymmetry sources from mixing and oscillations in leptogenesis can be distinctly identified using the Kadanoff-Baym formalism, revealing their spectral structures and interference effects.

Contribution

It unambiguously isolates mixing and oscillation CP-asymmetry sources within the Kadanoff-Baym framework, analyzing their spectral structures without relying on particle number definitions.

Findings

Identifies mixing and oscillation contributions on different spectral shells.

Shows interference effects between mixing and oscillations.

Demonstrates consistency across different formalism realizations.

Abstract

We show how the two physically-distinct sources of CP-asymmetry relevant to scenarios of leptogenesis: (i) resonant mixing and (ii) oscillations between different flavours can be unambiguously identified within the Kadanoff-Baym formalism. These contributions are isolated by analyzing the spectral structure of the non-equilibrium propagators without relying on the definition of particle number densities. The mixing source is associated with the usual mass shells, whereas the oscillation source is identified with a third intermediate shell. In addition, we identify terms lying on the oscillation shell that can be interpreted as the destructive interference between mixing and oscillation. We confirm that identical shell structure is obtained in both the Heisenberg- and interaction-picture realizations of the Kadanoff-Baym formalism. In so doing, we illustrate the self-consistency and complementarity of these two approaches. The interaction-picture approach in particular has the advantage that it may be used to analyze all forms of mass spectra from quasi-degenerate through to hierarchical.