632 research outputs found

### Cosmic Colored Black Holes

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

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

### Critical behavior of gravitating sphalerons

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

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

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

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

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

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

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

- …