Esteban Calzetta

TL;DR: This paper treats a system of self-interacting bosons described by λφ4 scalar fields in flat space and adopts the closed-time-path (CTP) functional formalism and uses a two-particle irreducible (2PI) representation for the effective action.

TL;DR: The capability of the closed-time-path formalism of dealing with Feynman, causal, and correlation functions on the same footing makes it a potentially powerful and versatile technique for treating nonequilibrium statistical properties of dynamical systems as in early-Universe quantum processes.

TL;DR: In this paper, the key ideas from nonequilibrium statistical mechanics and powerful methodology from quantum field theory are brought together to capture the essence of none-quilibrium quantum field theories.

TL;DR: It is shown that when the quantum to classical transition is properly treated, with due consideration of the relation of decoherence, noise, fluctuation and dissipation, the amplitude of density contrast predicted falls in the acceptable range without requiring a fine tuning of the coupling constant of the inflation field.

TL;DR: The old framework of semiclassical gravity is extended to that based on a Langevin-type equation, where the dynamics of the fluctuations of spacetime is driven by the quantum fluctuations of the matter field, useful for the investigation of quantum processes in the early Universe involving fluctuations, vacuum instability, and phase transition phenomena as well as the nonequilibrium thermodynamics of black holes.