Physics
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phrvd..56.6351d&link_type=abstract
Physical Review D (Particles, Fields, Gravitation, and Cosmology), Volume 56, Issue 10, 15 November 1997, pp.6351-6362
Physics
4
Wave Generation And Sources, Quantum Field Theory In Curved Spacetime, Thermodynamic Processes, Conduction, Convection, Equations Of State
Scientific paper
The inequivalence of vacua at different instants of time leads to the production of tensor perturbations (``gravitational waves'') in scales larger than the Hubble radius. During noninflationary periods of expansion, the very long tensor perturbations become effective gravitational waves as they enter the Hubble length, thus adding new contributions to the energy density associated with the subhorizon waves ρg. It is shown that this phenomenom can be described as a process of production of effective gravitons by using the macroscopic formalism to matter creation based on the thermodynamics of open systems. A creation pressure term is introduced in the continuity equation obeyed by ρg in order to deal with this process. This allows the derivation of a dynamical equation for the scale factor a(t) that takes into account the effective gravitons back reaction. This equation is numerically solved for a model in which the universe suffers a transition from an arbitrary initial phase to a radiation-dominated period. If the barotropic index of the equation of state in the first epoch is close to 2/3, the back reaction of the effective gravitational waves makes a(t) deviate noticeably from the standard behavior a(t)~t1/2. The same phenomenom may happen during the matter-dominated era, which could affect theoretical calculations involving the age of the universe.
Alcaniz Jailson S.
Carvalho João C.
de Garcia Maia Márcio Roberto
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