The Reissner-Nordstr\"om-Tangherlini solution from graviton and photon emission processes

Abstract

It is known that the canonical quantization of general relativity leads to a non-renormalizable theory, which however with the modern tools of effective field theories it is possible to make well-defined at low energies. What is emerging nowadays is that recovering general relativity from the classical limit of scattering amplitudes seems more efficient than actually solve the Einstein equations. The thesis then aims to explore the state-of-the-art strategies to recover classical gravitational observables from quantum computations and apply them in order to reconstruct the Reissner-Nordstr\"om-Tangherlini solution, which is the generalization to arbitrary dimensions of the Reissner-Nordstr\"om one, from the classical limit of scattering amplitudes of charged scalars. In the first part of the thesis, we recover the most generic energy-ordered effective action which is compatible with the symmetries of the theory, and then we discuss the classical limit from which it is possible to obtain back classical gravitational observables out of quantum computations. The state-of-the-art techniques to extract the classical contributions out of graviton emission amplitudes are reviewed, and they are applied to the context of a theory which is also coupled to the electromagnetic field. Since divergences arise in four and five dimensions it is crucial to define non-minimal couplings with the purpose of canceling such singularities and obtaining finite results. In the end, the considerations employed in the metric case are used to recover the electromagnetic potential associated to the black hole solution through the classical limit of photon emission processes. Also in this case there appear divergences that have to be renormalized. One of the most important outcomes is that the counter-terms that have to be fixed in order to eliminate the poles are the same throughout the theory.