Spacelike Branes

Scalar field theories with appropriate potentials in Minkowski space can have timedependent classical solutions containing topological defects which correspond to S-branes i.e. branes all of whose tangential dimensions are spacelike. It is argued that such Sbranes arise in string theory as time-dependent solutions of the worldvolume tachyon field of an unstable D-brane or D-brane-anti-D-brane pair. Using the known coupling of the spacetime RR fields to the worldvolume tachyon it is shown that these S-branes carry a charge, defined as the integral of a RR field strength over a sphere (containing a time as well as spatial dimensions) surrounding the S-brane. This same charge is carried by SDbranes, i.e. Dirichlet branes arising from open string worldsheet conformal field theories with a Dirichlet boundary condition on the timelike dimension. The corresponding SDbrane boundary state is constructed. Supergravity solutions carrying the same charges are also found for a few cases.