Flavoured quantum Boltzmann equations from cQPA

TL;DR

This paper develops a quantum transport theory incorporating flavour and particle-antiparticle mixing using the coherent quasiparticle approximation, revealing significant effects on CP violation in baryogenesis models.

Contribution

It introduces an extended phase-space formalism with new spectral shells for coherence, providing explicit propagators and rules for quantum transport with flavour and particle-antiparticle mixing.

Findings

Particle-antiparticle coherence influences CP-violating flavour mixing.

Coherence effects are significant even in slowly-varying backgrounds.

The formalism relates coherence solutions to squeezed states.

Abstract

We develop a Boltzmann-type quantum transport theory for interacting fermion and scalar fields including both flavour and particle-antiparticle mixing. Our formalism is based on the coherent quasiparticle approximation (cQPA) for the 2-point correlation functions, whose extended phase-space structure contains new spectral shells for flavour- and particle-antiparticle coherence. We derive explicit cQPA propagators and Feynman rules for the transport theory. In particular the nontrivial Wightman functions can be written as composite operators $\sim {\cal A} F {\cal A}$, which generalize the usual Kadanoff-Baym ansatz. Our numerical results show that particle-antiparticle coherence can strongly influence CP-violating flavour mixing even for relatively slowly-varying backgrounds. Thus, unlike recently suggested, these correlations cannot be neglected when studying asymmetry generation due to time-varying mass transition, for example in electroweak-type baryogenesis models. Finally, we show that the cQPA coherence solutions are directly related to squeezed states in the more familiar operator formalism.