Theory HEP Seminar

Backreaction in Quantum Cosmology

Susanne Schander

FAU Erlangen and Perimeter Institute

Several approaches to quantum gravity suggest that the big bang singularity is resolved and is often replaced by a big bounce. This raises the question of whether there are phenomenological consequences of such a scenario. As the physics involved in particular concerns the Planck era before inflation, one expects that quantum backreaction between the homogeneous and inhomogeneous degrees of freedom cannot be neglected in this regime. After a brief introduction to these concepts and the current status of the phenomenology involved, we review space adiabatic perturbation theory (SAPT) which was invented by Panati, Spohn and Teufel as an extension of the well known Born-Oppenheimer approach (BOA) for quantum mechanical systems with backreaction. We explain why BOA is insufficient for quantum cosmology and why an extension of SAPT to quantum field theory is non-trivial. Finally we apply SAPT to quantum backreaction in cosmology, list which challenges had to be overcome and present the current status of our calculations.