https://doi.org/10.1140/epjc/s10052-021-09874-3
Regular Article - Theoretical Physics
Cutting rules on a cylinder: a simplified diagrammatic approach to quantum kinetic theory
Department of Theoretical Physics, Comenius University in Bratislava, Mlynská dolina, 84248, Bratislava, Slovak Republic
Received:
13
October
2021
Accepted:
23
November
2021
Published online:
1
December
2021
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.
© The Author(s) 2021
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