MULTIPLE FIELD SCALAR-TENSOR THEORIES OF GRAVITY AND COSMOLOGY

We consider multiple scalar fields coupled to gravity, with special attention given to two-field theories. First, the conditions necessary for these theories to exactly meet solar system tests are given. We find, in particular, that these constraints require that some scalar kinetic terms be non-positive-definite. Next, we investigate the cosmological evolution of the fields to see if these conditions can be met. Solutions are found in the dust era, as well as radiation- and cosmological-constant-dominated epochs. The possibility of inflation in these theories is discussed. While power law growth of the scalar fields can yield the appropriate conditions to meet solar system constraints, these solutions are unstable.