Content area
Full Text
Astrophys Space Sci (2009) 323: 103106 DOI 10.1007/s10509-009-0052-4
L E T T E R
Lambda-universe in scalar-tensor gravity
Marcelo Samuel Berman
Received: 11 April 2009 / Accepted: 2 June 2009 / Published online: 12 June 2009 Springer Science+Business Media B.V. 2009
Abstract We present a lambda-Universe, in scalar-tensor gravity, reviewing Berman and Trevisans inationary case (Berman and Trevisan in Int. J. Theor. Phys., 2009) and then we nd a solution for an accelerating power-law scale-factor.
The negativity of cosmic pressure implies acceleration of the expansion, even with < 0. The cosmological term, and the coupling constant, are in fact, time-varying.
Keywords Lambda-term Scalar-tensor Power-laws
Scale-factors Cosmology
PACS 98.80.-k 98.80.Jk 98.80.Hw
1 Introduction
It would be very deceiving whether a scalar-tensor gravity accelerating lambda-model, would not reduce to the General Relativistic eld equations in the long run. We show here, that this is not the case.
New evidence for the acceleration of the expansion of the present Universe, has been recently gathered from many sources (Weinberg 2008). Barrow (1993) has pointed out the possible relevance of scalar-tensor gravity theories in the study of the Universe. He obtained exact solutions for homogeneous and isotropic cosmologies in vacuum and radiation cases, for a variable coupling constant, = (),
where stands for the scalar eld. The inationary phase
M.S. Berman ( )
Instituto Albert Einstein/Latinamerica, Av. Candido Hartmann, 575 #17, 80730-440, Curitiba, PR, Brazile-mail: mailto:[email protected]
Web End [email protected]
in such theory was studied by us recently (Berman and Trevisan 2009). We now tackle the present accelerating phase, and employ the same method of the prior paper, in order to obtain an adequate solution.
For Brans-Dicke original theory, Berman (1990a) has compared the solutions thereof obtained, with general relativistic ones. Furthermore, Berman (1990b) has studied B.D. theory with power-law scale-factors and time-dependent cosmological terms. At the same time, Berman (1991a) studied the same problem in General Relativity, and, then, a variable gravitational constant in an ad-hoc general relativistic format, was dealt with by Berman (1991b).
Berman and Som (1990) studied the same problem in the context of a B.D. theory endowed with a variable cosmological constant. For scalar-tensor theories, consult the books by Berman (2007a), Faraoni (2004), and Fujii and Maeda (2003). In Berman (2007b), we nd a rationale for...