*Review* **Fundamental Theory of Torsion Gravity**

**Luca Fabbri**

DIME, Metodi e Modelli Matematici, Università di Genova, Via all'Opera Pia 15, 16145 Genova, Italy; fabbri@dime.unige.it

**Abstract:** In this work, we present the general differential geometry of a background in which the space–time has both torsion and curvature with internal symmetries being described by gauge fields, and that is equipped to couple spinorial matter fields having spin and energy as well as gauge currents: torsion will turn out to be equivalent to an axial-vector massive Proca field and, because the spinor can be decomposed in its two chiral projections, torsion can be thought as the mediator that keeps spinors in stable configurations; we will justify this claim by studying some limiting situations. We will then proceed with a second chapter, where the material presented in the first chapter will be applied to specific systems in order to solve problems that seems to affect theories without torsion: hence the problem of gravitational singularity formation and positivity of the energy are the most important, and they will also lead the way for a discussion about the Pauli exclusion principle and the concept of macroscopic approximation. In a third and final chapter, we are going to investigate, in the light of torsion dynamics, some of the open problems in the standard models of particles and cosmology which would not be easily solvable otherwise.

**Keywords:** torsion-gravity; electrodynamics; spinors

**Citation:** Fabbri, L. Fundamental Theory of Torsion Gravity. *Universe* **2021**, *7*, 305. https://doi.org/ 10.3390/universe7080305

Academic Editors: Antonino Del Popolo and Matteo Luca Ruggiero

Received: 8 July 2021 Accepted: 15 August 2021 Published: 18 August 2021

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