Induced non-local cosmology
First author: Leonardo Giani
We investigate the cosmological implications of an effective gravitational action, inspired by Sakharov’s idea of induced gravity, containing non-local contributions from the operator $\left(\Box +\beta \right)^{-1} R$. The $\beta$ term is a novel feature in the panorama of non-local models of gravity, and arises naturally within Sakharov theory from the potential of a non-minimally coupled scalar field after a spontaneous symmetry breaking takes place. In this class of models the non-local contribution can acquire an oscillatory behaviour, thereby avoiding the divergence of the Hubble parameter at late times, which is another characteristic feature of the non-local models treated in the literature. Furthermore, the effective gravitational coupling $G_{\rm eff}$ inherits the oscillatory behaviour, resulting in alternating epochs of stronger and weaker gravity. Interestingly, this framework can describe a higher value for the Hubble factor today whilst potentially suppressing the growth of structures during the matter dominated epoch, providing a tool to catch \textit{two birds with one stone}, i.e. addressing at the same time both the $H_0$ and the $\sigma_8$ tensions.