Nonequilibrium evolution of scalar fields in FRW cosmologies

Journal Article · Tue Mar 15 04:00:00 EST 1994 · Physical Review, D (Particles Fields); (United States)

DOI:https://doi.org/10.1103/PhysRevD.49.2769· OSTI ID:5213548

Boyanovsky, D ^[1]; de Vega, H J ^[2]; Holman, R ^[3]

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1. Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)
2. Laboratoire de Physique Theorique et Hautes Energies, Universite Pierre et Marie Curie (Paris VI), Tour 16, 1er. etage, 4, Place Jussieu 75252 Paris, Cedex 05 (France)
3. Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

We derive the effective equations for the out of equilibrium time evolution of the order parameter and the fluctuations of a scalar field theory in spatially flat FRW cosmologies. The calculation is performed both to one loop and in a nonperturbative, self-consistent Hartree approximation. The method consists of evolving an initial functional thermal density matrix in time and is suitable for studying phase transitions out of equilibrium. The renormalization aspects are studied in detail and we find that the counterterms depend on the initial state. We investigate the high temperature expansion and show that it breaks down at long times. We also obtain the time evolution of the initial Boltzmann distribution functions, and argue that to one-loop order or in the Hartree approximation the time evolved state is a squeezed'' state. We illustrate the departure from thermal equilibrium by numerically studying the case of a free massive scalar field in de Sitter and radiation-dominated cosmologies. It is found that a suitably defined nonequilibrium entropy per mode increases linearly with comoving time in a de Sitter cosmology, whereas it is [ital not] a monotonically increasing function in the radiation-dominated case.

• OSTI ID: 5213548
• Journal Information: Physical Review, D (Particles Fields); (United States), Journal Name: Physical Review, D (Particles Fields); (United States) Vol. 49:6; ISSN 0556-2821; ISSN PRVDAQ
• Country of Publication: United States
• Language: English

Related Subjects

662110* -- General Theory of Particles & Fields-- Theory of Fields & Strings-- (1992-)
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CALCULATION METHODS
COSMOLOGICAL MODELS
DENSITY MATRIX
DISTRIBUTION FUNCTIONS
ENTROPY
EQUILIBRIUM
FLUCTUATIONS
FUNCTIONS
HARTREE-FOCK METHOD
MATHEMATICAL MODELS
MATRICES
ORDER PARAMETERS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
RENORMALIZATION
SCALAR FIELDS
THERMAL EQUILIBRIUM
THERMODYNAMIC PROPERTIES
VARIATIONS