Noise and fluctuations in semiclassical gravity

Journal Article · Wed Jun 15 00:00:00 EDT 1994 · Physical Review, D (Particles Fields); (United States)

DOI:https://doi.org/10.1103/PhysRevD.49.6636· OSTI ID:7239163

Calzetta, E ^[1]; Hu, B L ^[2]

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1. Instituto de Astronomia y Fisica del Espacio and Facultad de Ciencias Exactas y Naturales, Buenos Aires (Argentina)
2. Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)

We continue our earlier investigation of the back reaction problem in semiclassical gravity with the Schwinger-Keldysh or closed-time-path (CTP) functional formalism using the language of the decoherent history formulation of quantum mechanics. Making use of its intimate relation with the Feynman-Vernon influence functional method, we examine the statistical mechanical meaning and show the interrelation of the many quantum processes involved in the back reaction problem, such as particle creation, decoherence, and dissipation. We show how noise and fluctuation arise naturally from the CTP formalism. We derive an expression for the CTP effective action in terms of the Bogolubov coefficients and show how noise is related to the fluctuations in the number of particles created. In so doing we have extended the old framework of semiclassical gravity, based on the mean field theory of Einstein equation with a source given by the expectation value of the energy-momentum tensor, 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. This generalized framework is useful for the investigation of quantum processes in the early Universe involving fluctuations, vacuum stability, and phase transition phenomena as well as the nonequilibrium thermodynamics of black holes. It is also essential to an understanding of the transition from any quantum theory of gravity to classical general relativity.

• OSTI ID: 7239163
• Journal Information: Physical Review, D (Particles Fields); (United States), Vol. 49:12; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
FLUCTUATIONS
GRAVITATION
SEMICLASSICAL APPROXIMATION
NOISE
CREATION OPERATORS
QUANTUM MECHANICS
STATISTICAL MECHANICS
MATHEMATICAL OPERATORS
MECHANICS
QUANTUM OPERATORS
VARIATIONS
661310* - Relativity & Gravitation- (1992-)
661100 - Classical & Quantum Mechanics- (1992-)
661300 - Other Aspects of Physical Science- (1992-)