June 28, 2022 at 2 p.m. in Lorentz room (Staudingerweg 7, 5th floor) and via Zoom

Mathias Becker

Sebastian Schenk

Yong Xu

Spectral functions in quantum gravity and gauge theories
Manuel Reichert (University of Sussex)

Over the past decades, the asymptotic safety scenario has matured into a viable contender for a consistent theory of quantum gravity. A pressing open question concerns the unitarity of the theory. I will present important steps towards tackling this issue and show the first direct computation of the graviton spectral function in asymptotically safe quantum gravity with a novel Lorentzian renormalisation group approach. The resulting graviton spectral function displays a massless one-graviton peak and a positive multi-graviton continuum with an asymptotically safe scaling for large spectral values, though being gauge-dependent. To understand the intricacies, I will contrast this to a perturbatively well-controlled computation of spectral functions in gauge theories with an infrared Banks-Zaks fixed point. I will indicate consequences for scattering amplitudes and unitarity.