TIME-SYMMETRICAL INITIAL DATA SETS IN 4-DIMENSIONAL DILATON GRAVITY

I study the time-symmetric initial-data problem in theories with a mas sless scalar field (dilaton), free or coupled to a Maxwell held in the stringy way, finding different initial-data sets describing an arbitr ary number of black holes with arbitrary masses, charges, and asymptot ic value of the dilaton. The presence of the scalar held gives rise to a number of interesting effects. The mass and charges of a single bla ck hole are different in its two asymptotically hat regions across the Einstein-Rosen bridge. The same happens to the value of the dilaton a t infinity. This forbids the identification of these asymptotic region s in order to build (Misner) wormholes in the most naive way. Using di fferent techniques, I find regular initial data for stringy wormholes. The price paid is the existence singularities in the dilaton held. Th e presence of a single-valued scalar seems to constrain strongly the a llowed topologies of the initial spacelike surface. Other kinds of sca lar fields (taking values on a circle or being defined up to an additi ve constant) are also briefly considered.