Semiclassical Approximation meets Keldysh-Schwinger diagrammatic technique: Scalar ${\phi }^4$

Abstract

We study the evolution of the non-equilibrium quantum fields from a highly excited initial state in two approaches: the standard Keldysh-Schwinger diagram technique and the semiclassical expansion. We demonstrate explicitly that these two approaches coincide if the coupling constant $g$ and the Plank constant $\hslash$ are small simultaneously. Also, we discuss loop diagrams of the perturbative approach, which are summed up by the leading order term of the semiclassical expansion. As an example, we consider shear viscosity for the scalar field theory at the leading semiclassical order. We introduce the new technique that unifies both semiclassical and diagrammatic approaches and open the possibility to perform the resummation of the semiclassical contributions.

arXiv comment10 pages, many diagrams

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Cited by in corpus (10)

• The Open Effective Field Theory of Inflation
• The Schwinger-Keldysh Coset Construction
• An Open Effective Field Theory for light in a medium
• Quantum quenches in an interacting field theory: full quantum evolution vs. semi-classical approximations
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• Enhancement of particle creation in nonlinear resonant cavities
• Local quench within the Keldysh technique
• Quantitative classicality in cosmological interactions during inflation
• The Propagator Matrix Reloaded