Quantum Fluctuations and Curvature Singularities in Jackiw-Teitelboim Gravity

The Jackiw-Teitelboim gravity with the matter degrees of freedom is considered. The classical model is exactly solvable and its solutions describe non-trivial gravitational scattering of matter wave-packets. For huge amount of the solutions the scattering space-times are free of curvature singularities. However, the quantum corrections to the field equations inevitably cause the formation of (thunderbolt) curvature singularities, vanishing only in the limit $\hbar\to 0$. The singularities cut the space-time and disallow propagation to the future.The model is inspired by the dimensional reduction of 4-d pure Einstein gravity, restricted to the space-times with two commuting space-like Killing vectors. The matter degrees of freedom also stem from the 4-d ansatz. The measures for the continual integrations are judiciously chosen and one loop contributions (including the graviton and the dilaton ones) are evaluated. For the number of the matter fields $N=24$ we obtain even the exact effective action, applying the DDK-procedure. The effective action is nonlocal, but the semiclassical equations can be solved by using some theory of the Hankel transformations.