From Gaussian Reference Fluids to Primordial Perturbations: the Role of Time in Quantum Gravity, Dr. Giulia Maniccia, Sapienza University of Rome

The absence of an external time parameter in General Relativity creates a conflict with Quantum Field Theory, commonly referred to as the “problem of time”. Various approaches, ranging from the canonical framework to relational formalisms, have been proposed to address this issue.
In the first part of the talk, I will examine time constructions within the canonical WKB (perturbative) framework, demonstrating how certain conceptual challenges can be addressed by introducing a “Gaussian reference fluid”. Inspired by the work of Kuchař and Torre, this fluid is here treated as a fast-matter component within a Born-Oppenheimer-like scheme.
In the second part, I will present the ongoing effort to reformulate such models within a fully gauge-invariant formalism, taking fluid perturbations into account, incorporating fluid perturbations as suggested by recent studies in the reduced phase space framework.
On a cosmological scale, I will demonstrate how the perturbative Gaussian fluid approach leads to a breaking of scale invariance in the primordial power spectrum in the exact de Sitter phase.