Speaker
Description
In loop quantum cosmology (LQC), the classical big bang singularity is replaced by a quantum bounce. This raises the possibility that pre-inflationary quantum gravity effects could leave observable imprints on primordial cosmological perturbations. However, extracting such signatures requires assumptions about the evolution of perturbations through the high curvature regime and their initial quantum state.
This talk examines the robustness of analytic predictions for the primordial power spectrum in hybrid LQC, focusing on the recently proposed non-oscillatory vacuum state with asymptotic Hamiltonian diagonalisation. Following a brief overview of different approaches to cosmological perturbations in LQC, the extent to which predicted primordial signatures depend on detailed modelling of the bounce will be investigated. In particular, the talk compares within the hybrid approach different approximations to the time dependent effective mass of the perturbations near the bounce, including the Pöschl-Teller potential commonly used in analytic treatments. The resulting power spectra are found to be largely insensitive to these details, provided that the characteristic scale associated with the bounce is correctly captured.
As an outlook, the possible implications of moving beyond the treatment of perturbations on an effective modified cosmological background are discussed, together with the first steps towards deriving their dynamics from an underlying 4D covariant theory of modified gravity with a homogeneous cosmological sector that reproduces the effective dynamics of LQC.