Block-orthogonal brane systems, black holes and wormholes

Multidimensional cosmological, static spherically symmetric and Euclidean configurations are described in a unified way for gravity interacting with several dilatonic fields and antisymmetric forms, associated with electric and magnetic p -branes. Exact solutions are obtained when certain vectors, built from the input parameters of the model, are either orthogonal in minisuperspace, or form mutually orthogonal subsystems. Some properties of black hole solutions are indicated, in particular, a no-hair-type theorem and restrictions in models with multiple times. From the non-existence of Lorentzian wormholes, a universal restriction is obtained, applicable to orthogonal or blockorthogonal subsystems of any p -brane system. Euclidean wormhole solutions are found, their action and radii are explicitly calculated. Non-existence of Euclidean wormholes among the solutions of 11-dimensional supergravity is stated.