Renormalization of Perturbative Quantum Gravity

Abstract: General Relativity and Quantum Theory are the two main achievements of physics in the 20th century. Even though they have greatly enlarged the physical understanding of our universe, there are still situations which are completely inaccessible to us, most notably the Big Bang and the inside of black holes: These circumstances require a theory of Quantum Gravity — the unification of General Relativity with Quantum Theory. The most natural approach for that would be the application of the astonishingly successful methods of perturbative Quantum Field Theory to the graviton field, defined as the deviation of the metric with respect to a fixed background metric. Unfortunately, this approach seemed impossible due to the non-renormalizable nature of General Relativity. In this talk, I aim to give a pedagogical introduction to this topic, in particular to the Lagrange density, the Feynman graph expansion and the renormalization problem of their associated Feynman integrals. Finally, I will explain how this renormalization problem could be overcome by an infinite tower of gravitational Ward identities, as was established in my dissertation and the articles it is based upon, cf. arXiv:2210.17510 [hep-th].

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Gravitational redshift induces quantum interference

Abstract: General relativity and quantum mechanics are the two frameworks through which we understand Nature. To date, they have remained valid to great extent in their respective domains. Regardless of the myriad of attempts to find a unified theory that can describe all of observable phenomena, the quest for unification continues. One avenue for investigating the overlap of general relativity and quantum mechanics that is less ambitious but can still provide potentially observable and measurable predictions is that of quantum field theory in curved spacetime viewed through the lens of quantum information. In recent years, a great deal of attention has been given to this approach, which has provided novel and intriguing insights into phenomena that can be tested in the laboratory. We present an investigation in the quantum nature of the gravitational redshift, seeking to understand which are the expected quantum dynamics that lead to the effective classical observable effect. We discuss the classical regime and show that more intriguing aspects are expected. We conclude discussing potential for detection in space-based experiments.

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N-body simulation of the large-scale structure formation: manifestation of the cosmic screening effect

Abstract: In my talk, I consider the large-scale structure formation within the cosmic screening approach. The main feature of this approach is that a careful analysis of the perturbed Einstein equations leads to the conclusion that there is an exponential cutoff of the gravitational interaction on large (of the order of 2–3 Gpc) cosmological scales. This is a purely relativistic effect associated with the non-linearity of Einstein's equations. To confirm this effect numerically, we perform the N-body simulation employing the relativistic code “gevolution” modified to our approach. First, we obtain power spectra for scalar and vector metric perturbations to show that both “gevolution” and “screening” approaches are in very good agreement between each other. However, the “screening” code consumes less computational time, saving almost 40% of CPU (central processing unit) hours. Then, we perform N-body simulations of the power spectra of the mass density contrast in a box with a comoving size of 5.632 Gps. We find that these spectra cease to depend on time for scales beyond the cosmic screening length. This is a clear manifestation of the cosmic screening effect.

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