Scalar-tensor cosmologies in a minisuperspace formulation: A case study

Abstract

We revisit a general minisuperspace (MSS) formalism for scalar tensor Friedmann-Lema\^{\i}tre-Robertson-Walker type cosmological models in an arbitrary frame with a perfect fluid source. We discuss how to impose Cauchy data on the corresponding dynamical system in order to reconstruct a standard ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$) cosmological model. So far, the integrability of such models has been extensively studied in the Einstein or Jordan frames mainly. We extend these studies to an arbitrary frame taking into account nonminimal coupling between matter and gravity. To this aim we explore a gauge freedom associated with a choice of lapse function. We show that particular isothermal MSS coordinates are related with Einstein frames representing solution equivalent classes and have some invariant meaning. This provides a new universal framework for investigating cosmic evolution in an arbitrary frame: analytical solutions obtained in the Einstein frame can be transformed back to the physical frame by making use of a conformal transformation and field redefinition. We also show how such a technique can be useful when applied to Wheeler-DeWitt quantum cosmology.