Novel ‘‘no-scalar-hair’’ theorem for black holes

We formulate a new ‘‘no-hair’’ theorem for black holes in general relativity which rules out a multicomponent scalar field dressing of any asymptotically flat, static, spherically symmetric black hole. The field is assumed to be minimally coupled to gravity, and to bear a non-negative energy density as seen by any observer, but its field Lagrangian need not be quadratic in the field derivatives. The proof centers on energy-momentum conservation and the Einstein equations. One kind of field ruled out is the Higgs field with a double (or multiple) well potential. The theorem is also proved for scalar-tensor gravity.