Non-abelian magnetic black strings versus black holes

We present $d+1-$dimensional pure magnetic Yang-Mills (YM) black strings (or $1-$branes) induced by the $d-$dimensional Einstein-Yang-Mills-Dilaton black holes. Born-Infeld version of the YM field makes our starting point which goes to the standard YM field through a limiting procedure. The lifting from black holes to black strings, (with less number of fields) is by adding an extra, compact coordinate. This amounts to the change of horizon topology from $S^{d-2}$ to a product structure. Our black string in $5-$dimensions is a rather special one, with uniform Hawking temperature and non-asymptotically flat structure. As the YM charge becomes large the string gets thinner to tend into a breaking point and transform into a $4-$% dimensional black hole.Comment: 5 pages no figure; Final version to appear in EPJ

Torsion-induced spin precession

We investigate the motion of a spinning test particle in a spatially-flat FRW-type space-time in the framework of the Einstein-Cartan theory. The space-time has a torsion arising from a spinning fluid filling the space-time. We show that for spinning particles with nonzero transverse spin components, the torsion induces a precession of particle spin around the direction of the fluid spin. We also show that a charged spinning particle moving in a torsion-less spatially-flat FRW space-time in the presence of a uniform magnetic field undergoes a precession of a different character.Comment: latex, 4 eps figure

Constraining spacetime torsion with LAGEOS

We compute the corrections to the orbital Lense-Thirring effect (or frame-dragging) in the presence of spacetime torsion. We derive the equations of motion of a test body in the gravitational field of a rotating axisymmetric massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi. We calculate the secular variations of the longitudes of the node and of the pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be used to constrain torsion parameters. We report the experimental constraints obtained using both the nodes and perigee measurements of the orbital Lense-Thirring effect. This makes LAGEOS and Gravity Probe B (GPB) complementary frame-dragging and torsion experiments, since they constrain three different combinations of torsion parameters

Hairy black holes in theories with massive gravitons

This is a brief survey of the known black hole solutions in the theories of ghost-free bigravity and massive gravity. Various black holes exist in these theories, in particular those supporting a massive graviton hair. However, it seems that solutions which could be astrophysically relevant are the same as in General Relativity, or very close to them. Therefore, the no-hair conjecture essentially applies, and so it would be hard to detect the graviton mass by observing black holes.Comment: References added. 20 pages, 3 figures, based on the talk given at the 7-th Aegean Summer School "Beyond Einstein's theory of gravity", September 201

Constant curvature f(R) gravity minimally coupled with Yang-Mills field

We consider the particular class of f(R) gravities minimally coupled with Yang - Mills (YM) field in which the Ricci scalar =R_{0}= constant in all dimensions d\geq4. Even in this restricted class the spacetime has unlimited scopes determined by an equation of state of the form P_{eff}={\omega}{\rho}. Depending on the distance from the origin (or horizon of a black hole) the state function {\omega}(r) takes different values. It is observed that {\omega}\rightarrow(1/3) (the ultra relativistic case in 4 - dimensions) and {\omega}\rightarrow-1 (the cosmological constant) are the limiting values of our state function {\omega}(r) in a spacetime centered by a black hole. This suggests that having a constant {\omega} throughout spacetime around a charged black hole in f(R) gravity with constant scalar curvature is a myth.Comment: 12 pages 2 figures, Some references and 2 figures are added with minor changes. Final version for publication in European Physical Journal

Classical Yang-Mills Black hole hair in anti-de Sitter space

The properties of hairy black holes in Einstein–Yang–Mills (EYM) theory are reviewed, focusing on spherically symmetric solutions. In particular, in asymptotically anti-de Sitter space (adS) stable black hole hair is known to exist for frak su(2) EYM. We review recent work in which it is shown that stable hair also exists in frak su(N) EYM for arbitrary N, so that there is no upper limit on how much stable hair a black hole in adS can possess