No-boundary wave function, Wheeler-DeWitt equation, and path integral analysis of the bouncing quantum cosmology

Bouncing models are alternatives to inflationary cosmology that replace the initial big bang singularity by a "bouncing" phase. A deeper understanding of the initial conditions of the universe, in these scenarios, requires knowledge of quantum aspects of bouncing models. In this work, we propose two classes of bouncing models that can be studied with great analytical ease and hence, provide a test bed for investigating more profound problems in quantum cosmology of bouncing universes. Our model's two key ingredients enable us to do straightforward analytical calculations: (i) a convenient parametrization of the minisuperspace of FRLW spacetimes and (ii) two distinct choices of the effective perfect fluids that source the background geometry of the bouncing universe. We study the quantum cosmology of these models using both the Wheeler-de Witt equations and the path integral approach. In particular, we found a bouncing model analogue of the no-boundary wave function and presented a Lorentzian path integral representation for the same. We also discuss the introduction of real scalar perturbations.