Varun Kher: Matter Spectral Functions from Quantum Gravity

We present a Lorentzian quantum gravity study coupled to a template matter sector with gauge fields, scalars and fermions. Provided quantum gravity offers an asymptotically safe UV-completion, we determine the photon and scalar two-point functions in the presence of gravitational fluctuations, and show that both possess a Källén-Lehmann spectral representation. Our results are achieved using functional renormalisation adapted for theories in Lorentzian signature. We explain why and how interactions with gravity modify both the infrared as well as the ultraviolet behaviour of matter spectral functions. We further present the corresponding form factors on the level of the quantum effective action. We conclude with a discussion on the implications of unitarity in the context of quantum gravity with particle physics.