The loop gravity string
Laurent Freidel, Alejandro Perez, Daniele Pranzetti

TL;DR
This paper explores boundary degrees of freedom in loop quantum gravity, revealing they can be described by auxiliary strings and a conformal field theory structure with Virasoro algebra at punctures.
Contribution
It introduces a generalized boundary term with the Immirzi parameter, leading to a novel string-like description of boundary degrees of freedom in quantum gravity.
Findings
Boundary degrees of freedom localize at punctures on the boundary sphere.
These degrees of freedom are effectively described by auxiliary strings with a 3D internal target space.
The boundary charges satisfy a Virasoro algebra with central charge c=3.
Abstract
In this work we study canonical gravity in finite regions for which we introduce a generalisation of the Gibbons-Hawking boundary term including the Immirzi parameter. We study the canonical formulation on a spacelike hypersuface with a boundary sphere and show how the presence of this term leads to an unprecedented type of degrees of freedom coming from the restoration of the gauge and diffeomorphism symmetry at the boundary. In the presence of a loop quantum gravity state, these boundary degrees of freedom localize along a set of punctures on the boundary sphere. We demonstrate that these degrees of freedom are effectively described by auxiliary strings with a 3-dimensional internal target space attached to each puncture. We show that the string currents represent the local frame field, that the string angular momenta represent the area flux and that the string stress tensor…
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