632 research outputs found

    Cosmic Colored Black Holes

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    We present spherically symmetric static solutions (a particle-like solution and a black hole solution) in the Einstein-Yang-Mills system with a cosmological constant.Although their gravitational structures are locally similar to those of the Bartnik-McKinnon particles or the colored black holes, the asymptotic behavior becomes quite different because of the existence of a cosmological horizon. We also discuss their stability by means of a catastrophe theory as well as a linear perturbation analysis and find the number of unstable modes.Comment: 12 pages, latex, 4 figures (available upon request

    THE NUMBER OF SPHALERON INSTABILITIES OF THE BARTNIK-McKINNON SOLITONS AND NON-ABELIAN BLACK HOLES

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    It is proven that there are precisely nn odd-parity sphaleron-like unstable modes of the nn-th Bartnik-McKinnon soliton and the nn-th non-abelian black hole solution of the Einstein-Yang-Mills theory for the gauge group SU(2)SU(2).Comment: one reference is adde

    Critical behavior of gravitating sphalerons

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    We examine the gravitational collapse of sphaleron type configurations in Einstein--Yang--Mills--Higgs theory. Working in spherical symmetry, we investigate the critical behavior in this model. We provide evidence that for various initial configurations, there can be three different critical transitions between possible endstates with different critical solutions sitting on the threshold between these outcomes. In addition, we show that within the dispersive and black hole regimes, there are new possible endstates, namely a stable, regular sphaleron and a stable, hairy black hole.Comment: Latex, 14 pages, 8 figure

    Mass of Colored Black Holes

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    New results pertaining to colored static black hole solutions to the Einstein-Yang-Mills equations are obtained. The isolated horizons framework is used to define the concept of Hamiltonian Horizon Mass of the black hole. An unexpected relation between the ADM and Horizon masses of the black hole solution with the ADM mass of the corresponding Bartnik-McKinnon soliton is found. These results can be generalized to other non-linear theories and they suggest a general testing bed for the instability of the corresponding hairy black holes.Comment: 8 pages, no figures, Revtex file. Minor changes made to clarify some formulas. References updated. Final version to appear in PRD/15

    Superplastic Deformation Behavior of High-Temperature Titanium Alloys VT8 and Ti6242S

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    Superplastic forming (SPF) is an effective process that allows for forming the sheet metal parts of complex configuration. Superplastic deformation behavior of conventional sheets of a high temperature titanium alloys VT8 и Ti6242S was studied by constant strain rate tests in a temperature range of 850–950 ∘C. The research identified the optimum superplastic temperature of studied alloys in a constant strain rate of 3 × 10−4 s −1 with elongation above 150 %.     Keywords: superplasticity, titanium alloys, stress, elongation

    Rotating Einstein-Yang-Mills Black Holes

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    We construct rotating hairy black holes in SU(2) Einstein-Yang-Mills theory. These stationary axially symmetric black holes are asymptotically flat. They possess non-trivial non-Abelian gauge fields outside their regular event horizon, and they carry non-Abelian electric charge. In the limit of vanishing angular momentum, they emerge from the neutral static spherically symmetric Einstein-Yang-Mills black holes, labelled by the node number of the gauge field function. With increasing angular momentum and mass, the non-Abelian electric charge of the solutions increases, but remains finite. The asymptotic expansion for these black hole solutions includes non-integer powers of the radial variable.Comment: 63 pages, 10 figure

    New Critical Behavior in Einstein-Yang-Mills Collapse

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    We extend the investigation of the gravitational collapse of a spherically symmetric Yang-Mills field in Einstein gravity and show that, within the black hole regime, a new kind of critical behavior arises which separates black holes formed via Type I collapse from black holes formed through Type II collapse. Further, we provide evidence that these new attracting critical solutions are in fact the previously discovered colored black holes with a single unstable mode.Comment: 13 pages, 4 figure

    Sigma Model on de Sitter Space

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    We discuss spherically symmetric, static solutions to the SU(2) sigma model on a de Sitter background. Despite of its simplicity this model reflects many of the features exhibited by systems of non-linear matter coupled to gravity e.g. there exists a countable set of regular solutions with finite energy; all of the solutions show linear instability with the number of unstable modes increasing with energy.Comment: 11 pages, latex2e, 1 figur

    Hairy black holes in theories with massive gravitons

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    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
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