Edge modes of gravity. Part II. Corner metric and Lorentz charges

• Published in: The journal of high energy physics Vol. 2020; no. 11; pp. 1 - 64
• Main Authors: Freidel, Laurent, Geiller, Marc, Pranzetti, Daniele
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.11.2020; Springer Nature B.V; Springer; SpringerOpen
• Subjects: Algebra; Classical and Quantum Gravitation; Classical Theories of Gravity; Decomposition; Elementary Particles; Gauge Symmetry; High energy physics; High Energy Physics - Theory; Isomorphism; Mathematical analysis; Models of Quantum Gravity; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum gravity; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; Space-Time Symmetries; String Theory; Symmetry; Classical Theories of Gravity; Space-Time Symmetries; Gauge Symmetry; Models of Quantum Gravity; symmetry: algebra; simplex; quantum gravity; unitarity; diffeomorphism; Casimir; gravitation: tetrad; phase space; sphere; invariance: Lorentz; noncommutative; BF model; potential: symplectic; space-time: foliation; quantization
• ISSN: 1029-8479; 1126-6708; 1029-8479
• DOI: 10.1007/JHEP11(2020)027

A bstract In this second paper of the series we continue to spell out a new program for quantum gravity, grounded in the notion of corner symmetry algebra and its representations. Here we focus on tetrad gravity and its corner symplectic potential. We start by performing a detailed decomposition of the various geometrical quantities appearing in BF theory and tetrad gravity. This provides a new decomposition of the symplectic potential of BF theory and the simplicity constraints. We then show that the dynamical variables of the tetrad gravity corner phase space are the internal normal to the spacetime foliation, which is conjugated to the boost generator, and the corner coframe field. This allows us to derive several key results. First, we construct the corner Lorentz charges. In addition to sphere diffeomorphisms, common to all formulations of gravity, these charges add a local sl (2 , ℂ) component to the corner symmetry algebra of tetrad gravity. Second, we also reveal that the corner metric satisfies a local sl (2 , ℝ) algebra, whose Casimir corresponds to the corner area element. Due to the space-like nature of the corner metric, this Casimir belongs to the unitary discrete series, and its spectrum is therefore quantized. This result, which reconciles discreteness of the area spectrum with Lorentz invariance, is proven in the continuum and without resorting to a bulk connection. Third, we show that the corner phase space explains why the simplicity constraints become non-commutative on the corner. This fact requires a reconciliation between the bulk and corner symplectic structures, already in the classical continuum theory. Understanding this leads inevitably to the introduction of edge modes.