Effective dynamics of scalar cosmological perturbations from quantum gravity

Abstract: We derive an effective dynamics for scalar cosmological perturbations from quantum gravity, in the framework of group field theory (GFT) condensate cosmology. The emergent spacetime picture is obtained from the mean field hydrodynamic regime of the fundamental theory, and physical observables are defined using a relational strategy applied at the same level of approximation, in terms of suitable collective states of the GFT field. The dynamical equations we obtain for volume and matter perturbations lead to the same solutions as those of classical general relativity in the long-wavelength, super-horizon limit, but differ in other regimes. These differences could be of phenomenological interest and make contact between fundamental quantum gravity models and cosmological observations, indicating new physics or limitations of the fundamental models or of the approximations leading to the effective cosmological dynamics.