1,728 research outputs found
Global Structure of a Black-Hole Cosmos and its Extremes
We analyze the global structure of a family of Einstein-Maxwell solutions
parametrized by mass, charge and cosmological constant. In a qualitative
classification there are: (i) generic black-hole solutions, describing a
Wheeler wormhole in a closed cosmos of spatial topology ; (ii)
generic naked-singularity solutions, describing a pair of ``point" charges in a
closed cosmos; (iii) extreme black-hole solutions, describing a pair of
``horned" particles in an otherwise closed cosmos; (iv) extreme
naked-singularity solutions, in which a pair of point charges forms and then
evaporates, in a way which is not even weakly censored; and (v) an
ultra-extreme solution. We discuss the properties of the solutions and of
various coordinate systems, and compare with the Kastor-Traschen
multi-black-hole solutions.Comment: 11 pages. Diagrams not include
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
When Black Holes Meet Kaluza-Klein Bubbles
We explore the physical consequences of a recently discovered class of exact
solutions to five dimensional Kaluza-Klein theory. We find a number of
surprising features including: (1) In the presence of a Kaluza-Klein bubble,
there are arbitrarily large black holes with topology S^3. (2) In the presence
of a black hole or a black string, there are expanding bubbles (with de Sitter
geometry) which never reach null infinity. (3) A bubble can hold two black
holes of arbitrary size in static equilibrium. In particular, two large black
holes can be close together without merging to form a single black hole.Comment: 23 pages, 5 figures, v2: few comments on stability modifie
Nonlinear spinor field in cosmology
Within the scope of Bianchi type VI (BVI) model the self-consistent system of
nonlinear spinor and gravitational fields is considered. Exact self-consistent
solutions to the spinor and gravitational field equations are obtained for some
special choice of spatial inhomogeneity and nonlinear spinor term. The role of
inhomogeneity in the evolution of spinor and gravitational field is studied.
Oscillatory mode of expansion of the BVI universe is obtained for some special
choice of spinor field nonlinearity.Comment: RevTex4, 19 pages, 4 figure
Making Anti-de Sitter Black Holes
It is known from the work of Banados et al. that a space-time with event
horizons (much like the Schwarzschild black hole) can be obtained from 2+1
dimensional anti-de Sitter space through a suitable identification of points.
We point out that this can be done in 3+1 dimensions as well. In this way we
obtain black holes with event horizons that are tori or Riemann surfaces of
genus higher than one. They can have either one or two asymptotic regions.
Locally, the space-time is isometric to anti-de Sitter space.Comment: LaTeX, 10 pages, 6 postscript figures, uses epsf.te
The Isaacson expansion in quantum cosmology
This paper is an application of the ideas of the Born-Oppenheimer (or
slow/fast) approximation in molecular physics and of the Isaacson (or
short-wave) approximation in classical gravity to the canonical quantization of
a perturbed minisuperspace model of the kind examined by Halliwell and Hawking.
Its aim is the clarification of the role of the semiclassical approximation and
the backreaction in such a model. Approximate solutions of the quantum model
are constructed which are not semiclassical, and semiclassical solutions in
which the quantum perturbations are highly excited.Comment: Revtex, 11 journal or 24 preprint pages. REPLACEMENT: A comment on
previous work by Dowker and Laflamme is corrected. Utah preprint
UU-REL-93/3/1
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