Abstract
A quantum physical projector is proposed for generally covariant theories which are derivable from a Lagrangian. The projector is the quantum analogue of the integral over the generators of finite one-parameter subgroups of the gauge symmetry transformations which are connected to the identity. Gauge variables are retained in this formalism, thus permitting the construction of spacetime area and volume operators in a tentative spacetime loop formulation of quantum general relativity.
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Salisbury, D.C. Quantum General Invariance and Loop Gravity. Foundations of Physics 31, 1105–1118 (2001). https://doi.org/10.1023/A:1017530508201
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DOI: https://doi.org/10.1023/A:1017530508201