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AbstactWe quantize the tachyon field in a static two dimensional dilaton gravity black hole background,and we calculate the Hawking radiation rate.We find that the thermal radiation flux,due to the tachyon field, is larger than the conformal matter one.We also find that massive scalar fields which do not couple to the dilaton,do not give any contribution to the thermal radiation, up to terms quadratic in the scalar curvature.

In an ungauged N = 1 supergravity theory defined on an arbitrary Kahlerian manifold we compute the divergent one-loop corrections to the bosonic part of the effective action. Although the theory is not renormalizable such a calculation may be of relevance in view of the fact that N = 1 supergravities emerge as effective nonrenormalizable theories in the low-energy limit of some superstring models. In our calculations we have committed ourselves neither to a particular four-dimensional geometry nor to a particular Kahlerian manifold. We pay special attention to the one-loop scalar potential of the theory. We show that, by a proper redefinition of the metric, geometric objects such as scalar curvature can be made not to interact with the scalars and the definition of the potential of the theory becomes in this way unambiguous.PACS number(s): 04.65. +e 534

We examine background solutions of black hole type arising from the string effective action in five dimensions. We derive the unique metric -dilaton vacuum which is a Schwarzschild type black hole. It is found that it can be extended to incorporate electric charge without changing the topology of the three space. Kalb-Ramond charge may also be introduced if the three space is closed. The basic features of the cosmology induced on a three brane evolving in this background are also discussed. 1