S. Carlip, MODULAR GROUP, OPERATOR ORDERING, AND TIME IN (2-DIMENSIONAL GRAVITY(1)), Physical review. D. Particles and fields, 47(10), 1993, pp. 4520-4524
A choice of time slicing in classical general relativity permits the c
onstruction of time-dependent wave functions in the ''frozen time'' Ch
ern-Simons formulation of (2 + 1)-dimensional quantum gravity. Because
of operator-ordering ambiguities, however, these wave functions are n
ot unique. It is shown that when space has the topology of a torus, su
itable operator orderings give rise to wave functions that transform u
nder the modular group as automorphic functions of arbitrary weights,
with dynamics determined by the corresponding Maass Laplacians on modu
li space.