We calculate the expectation value of the stress energy tensor for a massless dilaton-coupled 2D scalar field propagating on an extremal Reissner-Nordstrom black hole formed by the collapse of a timelike shell, showing its regularity on the horizon.
@article{arxiv.hep-th/0503090,
title = {Stress tensor for extreme 2D dilatonic Reissner-Nordstrom black holes},
author = {Serena Fagnocchi and Sara Farese},
journal= {arXiv preprint arXiv:hep-th/0503090},
year = {2009}
}