Two-point function for a Massless Minimally Coupled Scalar Field in a Collapsing Null Shell Spacetime*

The computation of the two-point function for a quantized massless minimally coupled scalar field will be discussed for a spacetime in which a black hole forms from the collapse of a spherically symmetric null shell in four dimensions. The focus will be on the contribution from the spherically symmetric modes.  These are computed in the region outside the shell and the event horizon using a recently developed method.  The results will be compared with the two-dimensional case which has previously been computed.  Understanding the behavior of the two-point function is a preliminary step toward the full numerical computation of the renormalized expected value of the stress-energy tensor.