787 research outputs found
Validity of semiclassical gravity in the stochastic gravity approach
In semiclassical gravity the back-reaction of the classical gravitational
field interacting with quantum matter fields is described by the semiclassical
Einstein equations. A criterion for the validity of semiclassical gravity based
on the stability of the solutions of the semiclassical Einstein equations with
respect to quantum metric perturbations is discussed. The two-point quantum
correlation functions for the metric perturbations can be described by the
Einstein-Langevin equation obtained in the framework of stochastic gravity.
These correlation functions agree, to leading order in the large limit,
with the quantum correlation functions of the theory of gravity interacting
with matter fields. The Einstein-Langevin equations exhibit runaway
solutions and methods to deal with these solutions are discussed. The validity
criterion is used to show that flat spacetime as a solution of semiclassical
gravity is stable and, consequently, a description based on semiclassical
gravity is a valid approximation in that case.Comment: Second Intenational Workshop DICE200
Quantum Noise and Fluctuations in Gravitation and Cosmology
We give a short update of our research program on nonequilibrium statistical
field theory applied to quantum processes in the early universe and black
holes, as well as the development of stochastic gravity theory as an extension
of semiclassical gravity and an intermediary in the 'bottom-up' approach to
quantum gravity.Comment: 16 pages Latex; small changes in a couple of footnote
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