# Torsion in quantum field theory through time-loops on Dirac materials

## TL;DR

This paper explores how torsion, modeled as time-loops, could influence Dirac materials like graphene, proposing theoretical scenarios and potential experimental signatures involving electromagnetic fields and dislocations.

## Contribution

It introduces a novel approach to incorporate time and torsion in Dirac materials, proposing the concept of time-loops and their measurable effects on electronic responses.

## Key findings

- Theoretical framework for torsion as time-loops in Dirac materials.
- Proposal of Gedankenexperiments involving electromagnetic fields and dislocations.
- Potential observable effects in nonlinear optical responses of graphene.

## Abstract

Assuming dislocations could be meaningfully described by torsion, we propose here a scenario based on the role of time in the low-energy regime of two-dimensional Dirac materials, for which coupling of the fully antisymmetric component of the torsion with the emergent spinor is not necessarily zero. Appropriate inclusion of time is our proposal to overcome well-known geometrical obstructions to such a program, that stopped further research of this kind. In particular, our approach is based on the realization of an exotic $time-loop$, that could be seen as oscillating particle-hole pairs. Although this is a theoretical paper, we moved the first steps toward testing the realization of these scenarios, by envisaging $Gedankenexperiments$ on the interplay between an external electromagnetic field (to excite the pair particle-hole and realize the time-loops), and a suitable distribution of dislocations described as torsion (responsible for the measurable holonomy in the time-loop, hence a current). Our general analysis here establishes that we need to move to a nonlinear response regime. We then conclude by pointing to recent results from the interaction laser-graphene that could be used to look for manifestations of the torsion-induced holonomy of the time-loop, e.g., as specific patterns of suppression/generation of higher harmonics.