Canonical formalism for compact sources

This thesis aims to describe the ADM formalism of General Relativity and to use the latter to describe a spherical compact source consisting of a perfect fluid. With two different choices for three-dimensional metric on hypersurfaces, we analyze the constraints of the system in the non-static case and the resulting equations of motion, both for canonical gravitational variables and those of matter. After examining some special cases, we also show that it is possible, in the case of static nature, to obtain the value of the Misner-Sharp mass from the Hamiltonian constraint, while near the trapping surfaces we obtain a relationship between the density of matter and the dynamic variables of the metric. Finally we propose a possible method for quantizing the constraints using the procedure that in the vacuum leads to the Wheeler-DeWitt equations

How-To compute EPRL spin foam amplitudes

Spin foam theory is a concrete framework for quantum gravity where numerical calculations of transition amplitudes are possible. Recently, the field became very active, but the entry barrier is steep, mainly because of its unusual language and notions scattered around the literature. This paper is a pedagogical guide to spin foam transition amplitude calculations. We show how to write an EPRL-FK transition amplitude, from the definition of the 2-complex to its numerical implementation using \texttt{sl2cfoam-next}. We guide the reader using an explicit example balancing mathematical rigor with a practical approach. We discuss the advantages and disadvantages of this approach and provide a novel look at a recently proposed approximation scheme.Comment: 28 pages with many colored figures. Paper published in the special issue "Probing the Quantum Space-Time" of Universe. v-2 Added introductory section. Matching published versio

Primordial fluctuations from quantum gravity: 16-cell topological model

We present a numerical analysis of an Hartle-Hawking state for the early universe, in the deep quantum regime, computed using the covariant Loop Quantum Gravity formalism, in a truncation defined by 16-cell and in a simplified case where the dynamics is defined by SU(2) BF theory. We compute mean geometry, fluctuations and correlations. The results are consistent with the hypothesis that refining the triangulation does not affect the global physical picture substantially.Comment: 17 page

Radiative corrections to the Lorentzian EPRL spin foam propagator

We numerically estimate the divergence of several two-vertex diagrams that contribute to the radiative corrections for the Lorentzian EPRL spin foam propagator. We compute the amplitudes as functions of a homogeneous cutoff over the bulk quantum numbers, fixed boundary data, and different Immirzi parameters, and find that for a class of two-vertex diagrams, those with fewer than six internal faces are convergent. The calculations are done with the numerical framework sl2cfoam-next.Comment: 20 pages, 11 figure

Preliminary evaluations of the environmental impact for the production of 99Mo by fusion neutrons

ENEA is developing an accelerator-driven 14 MeV neutron source exploiting the deuterium–tritium fusion reaction to produce 99Mo medical radioisotope as an alternative production route not based on fission reactors. It is expected that, during normal operation, a number of radionuclides, generated by means of neutron irradiation on the raw material (natural Molybdenum), will be produced and managed. The present manuscript, as foreseen by national law, discusses a hypothetical scenario to test the environmental screening models, in turn evaluating the mechanisms and parameters which affect and control the path of liquid effluents potentially released during normal operation of the facility. The aim is to estimate the amount of radioactivity to be operated and the fraction potentially discharged in this hypothetical scenario, so as to ensure that the radioactive material can be managed without any risk for the population and the environment, according to national regulations and thoroughly fulfilling the international guidelines

The New Sorgentina Fusion Source-NSFS: 14 MeV neutrons for fusion and beyond

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Preliminary Assessment of Radiolysis for the Cooling Water System in the Rotating Target of {SORGENTINA}-{RF}

The SORGENTINA-RF project aims at developing a 14 MeV fusion neutron source featuring an emission rate in the order of 5-7 x 10(13) s(-1). The plant relies on a metallic water-cooled rotating target and a deuterium (50%) and tritium (50%) ion beam. Beyond the main focus of medical radioisotope production, the source may represent a multi-purpose neutron facility by implementing a series of neutron-based techniques. Among the different engineering and technological issues to be addressed, the production of incondensable gases and corrosion product into the rotating target deserves a dedicated investigation. In this study, a preliminary analysis is carried out, considering the general layout of the target and the present choice of the target material

Studying the EPRL spinfoam self-energy

I present some recent progresses in the study of the EPRL self-energy amplitude. New numerical methods allow to analyze how the divergence scales, for which previous works provided very different lower and upper bounds. I show the role that the Immirzi parameter plays in the asymptotic behavior, and I discuss the dynamical expectation value of the dihedral angle boundary observable.Comment: 19 pages, contribution to the Proceedings of the 16th Marcel Grossmann Meeting (MG16 - July 2021

High-performance computing in covariant Loop Quantum Gravity

This Ph.D. thesis presents a compilation of the scientific papers I published over the last three years during my Ph.D. in loop quantum gravity (LQG). First, we comprehensively introduce spinfoam calculations with a practical pedagogical paper. We highlight LQG\u27s unique features and mathematical formalism and emphasize the computational complexities associated with its calculations. The subsequent articles delve into specific aspects of employing high-performance computing (HPC) in LQG research. We discuss the results obtained by applying numerical methods to studying spinfoams\u27 infrared divergences, or ``bubbles\u27\u27. This research direction is crucial to define the continuum limit of LQG properly. We investigate the self-energy diagram in LQG, analyzing the scaling of the divergence of the associated amplitude. Using the same technique, we compute the spinfoam amplitudes of a class of two-vertex diagrams. Besides divergent graphs, our investigations yield striking and surprising numerical evidence that spinfoam-containing bubbles can have finite transition amplitudes. Furthermore, we adapt Monte Carlo methods to the spinfoam formalism. We employ this technique to analyze the vertex renormalization amplitude. We find numerical solid indications that this amplitude is convergent, opening new perspectives for renormalizing large-volume infrared spinfoam bubbles. In spinfoam cosmology, we investigate the integration of HPC with Markov Chain Monte Carlo simulations, proving the potential to analyze the macroscopic properties of quantum spacetime. We perform a spinfoam refinement process starting from the simplest diagram, demonstrating the effectiveness of this hybrid approach and elucidating the connection of LQG observables with spacetime geometry. Furthermore, we apply the same technique to investigate the spinfoam with a 16-cell boundary using a topological model. Finally, we outline a numerical algorithm to compute the transition amplitude from a black hole to a ``white hole\u27\u27. The recently proposed hypothetical decay process via gravitational quantum tunneling is one of the most intriguing hypotheses on the future of black holes. We use the spinfoam approach and HPC to investigate this phenomenon by explicitly computing the associated transition amplitude. The advancements of HPC-assisted LQG research will hopefully enable the study of complex gravitational phenomena at unprecedented scales, paving the way for exploring previously inaccessible physical regimes