Tensor-Scalar Cosmological Models and Their Relaxation toward General Relativity

摘要

Cosmological models within general tensor-multi-scalar theories of gravity are studied. By isolating an autonomous evolution equation for the scalar fields, one shows that the expansion of the universe during the matter-dominated era tends to drive the scalar fields toward a minimum of the function alpha(phi) describing their coupling to matter, i.e. toward a state where the tensor-scalar theory becomes indistinguishable from general relativity. The two main parameters determining the efficiency of this natural attractor mechanism toward general relativity are the redshift at the beginning of the matter era (or equivalently the present cosmological matter density) and the curvature of the coupling function alpha(phi). Quantitative estimates for the present level of deviation from general relativity, as measured by the post-Newtonian parameters gamma - 1, beta - 1 and (G dot)/G, are derived, which give greater significance to future improvements of solar-system gravitational tests.