Special cosmological models derived from the semiclassical Einstein equation on flat FLRW space-times

Review Astronomy & Astrophysics

Backreaction in Cosmology

S. Schander et al.

Summary: This review investigates the question of backreaction in different approaches to cosmological perturbation theory, with a special focus on quantum theoretical aspects. It covers classical cosmological backreaction, semiclassical approaches such as semiclassical or stochastic gravity, and backreaction in quantum cosmology for the very early Universe. The main emphasis is on a recently proposed implementation of backreaction in quantum cosmology using a Born-Oppenheimer inspired method.

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES (2021)

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Article Physics, Multidisciplinary

Existence and Uniqueness of Solutions of the Semiclassical Einstein Equation in Cosmological Models

Paolo Meda et al.

Summary: The research establishes the existence and uniqueness of solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a quantum massive scalar field with arbitrary coupling. By using a linear unbounded operator, the inversion of the highest derivative is achieved in the expectation values of the stress-energy tensor, leading to a more regular inverse operator in the form of a retarded product. The proof of local existence and uniqueness of the solution is then obtained by applying the Banach fixed point theorem.

ANNALES HENRI POINCARE (2021)

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Article Physics, Multidisciplinary

The Cosmological Semiclassical Einstein Equation as an Infinite-Dimensional Dynamical System

Hanno Gottschalk et al.

Summary: The study presents a comprehensive framework for solving the semiclassical Einstein equation in cosmological spacetimes, demonstrating the existence of solutions for different quantum states. The approach involves a regularization procedure and methods related to Ovsyannikov's method, leading to the identification of maximal/global solutions for vacuum-like states and local solutions for thermal-like states. The equations developed do not exhibit the instability of the Minkowski solution as observed in previous works.

ANNALES HENRI POINCARE (2021)

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Article Astronomy & Astrophysics