Energy-momentum tensor of particles created in an expanding universe
- Theoretical Division T-8, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
We present a general formulation of the time-dependent initial value problem for a quantum scalar field of arbitrary mass and curvature coupling in a Friedmann-Robertson-Walker (FRW) cosmological model. We introduce an adiabatic number basis which has the virtue that the divergent parts of the quantum expectation value of the energy-momentum tensor <T{sub ab}> are isolated in the vacuum piece of <T{sub ab}>, and may be removed using adiabatic subtraction. The resulting renormalized <T{sub ab}> is conserved, independent of the cutoff, and has a physically transparent, quasiclassical form in terms of the average number of created adiabatic ''particles.'' By analyzing the evolution of the adiabatic particle number in de Sitter spacetime we exhibit the time structure of the particle creation process, which can be understood in terms of the time at which different momentum scales enter the horizon. A numerical scheme to compute <T{sub ab}> as a function of time with arbitrary adiabatic initial states (not necessarily de Sitter invariant) is described. For minimally coupled, massless fields, at late times the renormalized <T{sub ab}> goes asymptotically to the de Sitter invariant state previously found by Allen and Folacci, and not to the zero mass limit of the Bunch-Davies vacuum. If the mass m and the curvature coupling {xi} differ from zero, but satisfy m{sup 2}+{xi}R=0, the energy density and pressure of the scalar field grow linearly in cosmic time demonstrating that, at least in this case, back reaction effects become significant and cannot be neglected in de Sitter spacetime. (c) 1999 The American Physical Society.
- OSTI ID:
- 20215157
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 61, Issue 2; Other Information: PBD: 15 Jan 2000; ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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