Quantum effects near a point mass in 2+1 dimensional gravity
  We investigate the behaviour of classical and quantum fields in the conical space-time associated with a point mass in 2+1 dimensions. We show that the presence of conical boundary conditions alters the electrostatic field of a point charge leading to the presence of a finite self-force on the charge from the direction of the point mass exactly as if the point mass itself were charged. The conical space-time geometry also affects the zero point fluctuations of a quantum scalar field leading to the existence of a vacuum polarisation --- $\langle T_\mn \rangle$, in the 2+1 dimensional analog of the Schwarzschild metric. The resulting linearised semi-classical Einstein equations --- $G_\mn = 8 \pi G \langle T_\mn \rangle$, possess a well defined Newtonian limit, in marked contrast to the classical case for which no Newtonian limit is known to exist. An elegant reformulation of our results in terms of the method of images is also presented.   Our analysis also covers the non-static de Sitter--Schwarzschild metric in 2+1 dimensions, in which in addition to the vacuum polarisation, a non-zero vacuum flux ofenergy -- $\langle T_{rt} \rangle $ is also found to exist.As part of this analysis, we evaluate the scalar field propagator in an $n$-dimensional de Sitter space, 
Tarun Souradeep and Varun Sahni