Transition from accelerated to decelerated regimes in JT and CGHS cosmologiesM. H. Christmann, F. P. Devecchi, G. M. Kremer and C. M. Zanetti
Departamento de Física, Universidade Federal do Paraná Caixa Postal 19044, 81531-990, Curitiba, Brazil
(Received 14 April 2004; accepted in final form 29 June 2004)
In this work we discuss the possibility of positive-acceleration regimes, and their transition to decelerated regimes, in two-dimensional (2D) cosmological models. We use general relativity and the thermodynamics in a 2D space-time, where the gas is seen as the sources of the gravitational field. An early-Universe model is analyzed where the state equation of van der Waals is used, replacing the usual barotropic equation. We show that this substitution permits the simulation of a period of inflation, followed by a negative-acceleration era. The dynamical behavior of the system follows from the solution of the Jackiw-Teitelboim equations (JT equations) and the energy-momentum conservation laws. In a second stage we focus the Callan-Giddings-Harvey-Strominger model (CGHS model); here the transition from the inflationary period to the decelerated period is also present between the solutions, although this result depends strongly on the initial conditions used for the dilaton field. The temporal evolution of the cosmic-scale function, its acceleration, the energy density and the hydrostatic pressure are the physical quantities obtained through the analysis.
04.50.+h - Gravity in more than four dimensions, Kaluza-Klein theory, unified field theories; alternative theories of gravity.
98.80.-k - Cosmology.
© EDP Sciences 2004