Isotropic LQC and LQC--inspired Models with a massless scalar field as Generalised Brans--Dicke theories

Abstract

We explore whether generalised Brans -- Dicke theories, which have a scalar field $\Phi$ and a function $\omega(\Phi)$, can be the effective actions leading to the effective equations of motion of the LQC and the LQC--inspired models, which have a massless scalar field $\sigma$ and a function $f(m) \;$. We find that this is possible for isotropic cosmology. We relate the pairs $(\sigma, f)$ and $(\Phi, \omega)$ and, using examples, illustrate these relations. We find that near the bounce of the LQC evolutions for which $f(m) = sin \; m$, the corresponding field $\Phi \to 0$ and the function $\omega(\Phi) \propto \Phi^2 \;$. We also find that the class of generalised Brans -- Dicke theories, which we had found earlier to lead to non singular isotropic evolutions, may be written as an LQC--inspired model. The relations found here in the isotropic cases do not apply to the anisotropic cases, which perhaps require more general effective actions.