Coherent quasiparticle approximation cQPA and nonlocal coherence

TL;DR

This paper introduces an extended quasiparticle approximation (cQPA) that captures quantum coherence effects in noninteracting and interacting fermions and bosons, with applications to particle production and baryogenesis.

Contribution

It develops a novel phase space structure for Wigner functions, incorporating coherence solutions into the quasiparticle framework for the first time.

Findings

New shell solutions encode quantum coherence between states.

Derived a self-consistent evolution equation for the density matrix.

Demonstrated applications to baryogenesis and decoherence studies.

Abstract

We show that the dynamical Wigner functions for noninteracting fermions and bosons can have complex singularity structures with a number of new solutions accompanying the usual mass-shell dispersion relations. These new shell solutions are shown to encode the information of the quantum coherence between particles and antiparticles, left and right moving chiral states and/or between different flavour states. Analogously to the usual derivation of the Boltzmann equation, we impose this extended phase space structure on the full interacting theory. This extension of the quasiparticle approximation gives rise to a self-consistent equation of motion for a density matrix that combines the quantum mechanical coherence evolution with a well defined collision integral giving rise to decoherence. Several applications of the method are given, for example to the coherent particle production, electroweak baryogenesis and study of decoherence and thermalization.