Cutting rules on a cylinder: a bottom-up approach to quantum kinetic theory for the early universe

Abstract

Nonequilibrium quantum field theory is often used to derive an approximation for the evolution of number densities and asymmetries in astroparticle models when a more precise treatment of quantum thermal effects is required. This work presents an alternative framework using the zero-temperature quantum field theory, $S$-matrix unitarity, and classical Boltzmann equation as starting points leading to a set of rules for calculations of thermal corrections to reaction rates. Statistical factors due to on-shell intermediate states are obtained from the cuts of forward diagrams with multiple spectator lines. It turns out that it is equivalent to cutting closed diagrams on a cylindrical surface.

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Cited by in corpus (9)

• What is the $i\epsilon$ for the S-matrix?
• Exposing the threshold structure of loop integrals
• Mass-derivative relations for leptogenesis
• Mass-derivative relations and unitarity constraints for $CP$ asymmetries at finite temperature
• Dirac leptogenesis from asymmetry wash-in via scatterings
• Cutting rules and positivity in finite temperature many-body theory
• Asymmetric dark matter from semi-annihilation: unitarity constraints and long-lived final states
• $CPT$ and unitarity constraints for higher-order $CP$ asymmetries at finite temperature
• Cutting rules on a cylinder and simplified diagrammatic approach to $CP$ violation in quantum kinetic theory