Some Cosmological Applications of Two Measures Theory

Abstract

Scale invariance is considered in the context of a gravitational theory where the action, in the first order formalism, is of the form S = \int L_{1} \Phi d^4x + \int L_{2}\sqrt{-g}d^4x where \Phi is a density built out of degrees of freedom independent of the metric. For global scale invariance, a "dilaton" \phi has to be introduced, with non-trivial potentials V(\phi)=f_{1}e^{\alpha\phi} in L_1 and U(\phi) = f_{2}e^{2\alpha\phi} in L_2. In the effective Einstein frame, this leads to a non-trivial \phi potential (of the Morse type) which has a flat region with energy density f_{1}^{2}/4f_{2} as \phi\to\infty. The addition of an R^{2} term produces an effective potential with two connected flat regions: one of the Planck scale, that can be responsible for early inflation, and another for the description of the present universe.