Space-time aspects of string theory are studied in the context of the low engery effective string theory. We consider d-dimensional charged dilaton gravity theories which can be interpreted as various low energy effective string theories in the d-dimensional target space. The theories have naked singularities, asymptotically flat and non-flat black holes. We show no-scalar-hair property and clarify the relationship between asymptotically flat and non-flat black holes.
The implications of the string duality to the space-time of the low energy effective string theory is considered using the (2+1)-dimensional gravity theories including a particular effective string theory. We find an analog of electric-magnetic duality trasformation in the axially symmetric and static cases. It is shown that the transformation can be related to T-duality and also can be used to generate new solutions from the known solutions.
We can describe physics of D-branes by supergravity for the distance scale much logner than the string size. The type IIB supergravity which describes intersecting D-strings and D 5-branes is studied. It is shown that their static S-wave sector contains naked singularity, asymptotically flat and non-flat black holes. We show no-hair property and clarify the relationship between asymptotically flat and non-flat black holes.