On gravitational defects, particles and strings

TL;DR

This paper develops a formalism for incorporating point particles and strings into four-dimensional gravity using a gauge theory approach, revealing how spinning matter and string dynamics emerge within this framework.

Contribution

It introduces a gauge-invariant method to include spinning particles and strings in gravity, connecting worldline and worldsheet actions to known physical models.

Findings

Worldline action describes a massive spinning particle.

Worldsheet action extends Nambu-Goto string with spinning effects.

Potential applications to quantum gravity models like spinfoams.

Abstract

We study the inclusion of point and string matter in the deSitter gauge theory, or MacDowell-Mansouri formulation of four dimensional gravity. We proceed by locally breaking the gauge symmetries of general relativity along worldlines and worldsheets embedded in the spacetime manifold. Restoring full gauge invariance introduces new dynamical fields which describe the dynamics of spinning matter coupled to gravity. We discuss the physical interpretation of the obtained formalism by studying the flat limit and the spinless case on arbitrary backgrounds. It turns out that the worldline action describes a massive spinning particle, while the worldsheet action contains the Nambu-Goto string augmented with spinning contributions. Finally, we study the gravity/matter variational problem and conclude by discussing potential applications of the formalism to the inclusion of the Nambu-Goto string in spinfoam models of four dimensional quantum gravity.