Gravitating monopole and its black hole solution in Brans-Dicke theory - art. no. 104049

We find a self-gravitating monopole and its black hole solution in Brans-Di cke (BD) theory. We mainly discuss the properties of these solutions in the Einstein frame and compare the solutions with those in general relativity (GR) on the following points. From the held distributions of the generic ty pe of self-gravitating monopole solutions, we find that the Yang-Mills pote ntial and the Higgs field hardly depend on the ED parameter for most of the solution. There is an upper Limit of the vacuum expectation value of the H iggs field to which a solution exists, as in GR. Since the ED scalar field has the effect of lessening an effective gauge charge, the upper limit in E D theory (in the omega=0 case) becomes about 30% larger than in GR. In some parameter ranges, then are two nontrivial solutions with the same mass, on e of which can be regarded as the excited state of the other. This is confi rmed by the analysis by catastrophe theory, which states that the excited s olution is unstable. We also find that the ED scalar field varies more for solutions of smaller horizon radii, which can be understood from the differ ences of the nontrivial structure outside the horizon. A scalar mass and th e thermodynamical properties of new solutions are also examined. Our analys is may give insight into solutions in other theories of gravity; particular ly, a theory with a dilaton field may show similar effects because of its c oupling to a gauge field. [S0556-2821(99)07220-3].