Dark energy fingerprints in the nonminimal Wu-Yang wormhole structure

We discuss new exact solutions to nonminimally extended Einstein-Yang-Mills equations describing spherically symmetric static wormholes supported by the gauge field of the Wu-Yang type in a dark energy environment. We focus on the analysis of three types of exact solutions to the gravitational field equations. Solutions of the first type relate to the model, in which the dark energy is anisotropic, i.e., the radial and tangential pressures do not coincide. Solutions of the second type correspond to the isotropic pressure tensor; in particular, we discuss the exact solution, for which the dark energy is characterized by the equation of state for a string gas. Solutions of the third type describe the dark energy model with constant pressure and energy density. For the solutions of the third type, we consider in detail the problem of horizons and find constraints for the parameters of nonminimal coupling and for the constitutive parameters of the dark energy equation of state, which guarantee that the nonminimal wormholes are traversable.Comment: 11 pages, 2 figures, accepted for publication in Phys. Rev.

Einstein-Maxwell-axion theory: Dyon solution with regular electric field

In the framework of Einstein-Maxwell-axion theory we consider static spherically symmetric solutions, which describe a magnetic monopole in the axionic environment. These solutions are interpreted as the solutions for an axionic dyon, the electric charge of which is composite, i.e., in addition to the standard central electric charge, it includes an effective electric charge induced by the axion-photon coupling. We focus on the analysis of that solutions, which are characterized by the electric field regular at the center. Special attention is paid to the solutions with the electric field, which is vanishing at the center, has the Coulombian asymptote and thus display an extremum at some distant sphere. Constraints on the electric and effective scalar charges of such an object are discussed.Comment: 11 pages, 4 figure

Nonminimal black holes with regular electric field

We discuss the problem of identification of coupling constants, which describe interactions between photons and space-time curvature, using exact regular solutions to the extended equations of the nonminimal Einstein-Maxwell theory. We argue the idea that three nonminimal coupling constants in this theory can be reduced to the single guiding parameter, which plays the role of nonminimal radius. We base our consideration on two examples of exact solutions obtained earlier in our works: the first of them describes a nonminimal spherically symmetric object (star or black hole) with regular radial electric field; the second example represents a nonminimal Dirac-type object (monopole or black hole) with regular metric. We demonstrate that one of the inflexion points of the regular metric function identifies a specific nonminimal radius, thus marking the domain of dominance of nonminimal interactions.Comment: 10 pages, 2 figures; based on talks presented at VII Black Holes Workshop, Aveiro, Portuga