Arbitrary static, spherically symmetric space-times as solutions of scalar-tensor gravity

It is shown that an arbitrary static, spherically symmetric metric can be presented as an exact solution of a scalar-tensor theory (STT) of gravity with certain nonminimal coupling function $f(\phi)$ and potential $U(\phi)$. The scalar field in this representation can change its nature from canonical to phantom on certain coordinate spheres. This representation, however, is valid in general not in the full range of the radial coordinate but only piecewise. Two examples of STT representations are discussed: for the Reissner-Nordstr\"om metric and for the Simpson-Visser regularization of the Schwarzschild metric (the so-called black bounce space-time).Comment: 8 pages, 1 figur

On the stability of spherically symmetric space-times in scalar-tensor gravity

We study the linear stability of vacuum static, spherically symmetric solutions to the gravitational field equations of the Bergmann-Wagoner-Nordtvedt class of scalar-tensor theories (STT) of gravity, restricting ourselves to nonphantom theories, massless scalar fields and configurations with positive Schwarzschild mass. We consider only small radial (monopole) perturbations as the ones most likely to cause an instability. The problem reduces to the same Schroedinger-like master equation as is known for perturbations of Fisher's solution of general relativity (GR), but the corresponding boundary conditions that affect the final result of the study depend on the choice of the STT and a particular solution within it. The stability or instability conclusions are obtained for the Brans-Dicke, Barker and Schwinger STT as well as for GR nonminimally coupled to a scalar field with an arbitrary parameter $\xi$.Comment: 16 pages, 4 figures, each of 2 part

Gravitating Sphaleron-Antisphaleron Systems

We present new classical solutions of Einstein-Yang-Mills-Higgs theory, representing gravitating sphaleron-antisphaleron pair, chain and vortex ring solutions. In these static axially symmetric solutions, the Higgs field vanishes on isolated points on the symmetry axis, or on rings centered around the symmetry axis. We compare these solutions to gravitating monopole-antimonopole systems, associating monopole-antimonopole pairs with sphalerons.Comment: 7 pages, 3 figure

New Black Hole Solutions with Axial Symmetry in Einstein-Yang-Mills Theory

We construct new black hole solutions in Einstein-Yang-Mills theory. They are static, axially symmetric and asymptotically flat. They are characterized by their horizon radius and a pair of integers (k,n), where k is related to the polar angle and n to the azimuthal angle. The known spherically and axially symmetric EYM black holes have k=1. For k>1, pairs of new black hole solutions appear above a minimal value of n, that increases with k. Emerging from globally regular solutions, they form two branches, which merge and end at a maximal value of the horizon radius. The difference of their mass and their horizon mass equals the mass of the corresponding regular solution, as expected from the isolated horizon framework.Comment: 11 pages, 3 figure

New Regular Solutions with Axial Symmetry in Einstein-Yang-Mills Theory

We construct new regular solutions in Einstein-Yang-Mills theory. They are static, axially symmetric and asymptotically flat. They are characterized by a pair of integers (k,n), where k is related to the polar angle and $n$ to the azimuthal angle. The known spherically and axially symmetric EYM solutions have k=1. For k>1 new solutions arise, which form two branches. They exist above a minimal value of n, that increases with k. The solutions on the lower mass branch are related to certain solutions of Einstein-Yang-Mills-Higgs theory, where the nodes of the Higgs field form rings.Comment: 11 pages, 7 figure