Speaker
Description
Using modern functional renormalisation adapted for theories in Lorentzian signature, and enhanced by new symmetry conditions to account for underlying Ward identities, we derive and solve flow equations directly for the Källén-Lehmann representation of propagators. Consistent results are found for several sets of renormalisation conditions yielding normalisable spectral functions for the graviton and the scalar graviton mode, in agreement with effective theory in the infrared. All resulting spectral functions are compatible with causality and unitarity. They provide direct access to the full quantum propagators and the quantum effective action up to quadratic order in the curvature. Renormalisation schemes that simplify the RG flows are identified, which paves the way for the computations of non-perturbative scattering amplitudes directly in Lorentzian signatures.
We also present several extensions of this framework. This includes the first Lorentzian spectral flow for the Newton coupling, and graviton spectral flows in schemes with improved control over diffeomorphism symmetry breaking. Implications for convergence of spectral flows are also indicated.
| Affiliation | University of Sussex |
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| Career status | PhD student |