1,098 research outputs found
Black strings in (4+1)-dimensional Einstein-Yang-Mills theory
We study two classes of static uniform black string solutions in a
(4+1)-dimensional SU(2) Einstein-Yang-Mills model. These configurations possess
a regular event horizon and corresponds in a 4-dimensional picture to axially
symmetric black hole solutions in an Einstein-Yang-Mills-Higgs-U(1)-dilaton
theory. In this approach, one set of solutions possesses a nonzero magnetic
charge, while the other solutions represent black holes located in between a
monopole-antimonopole pair. A detailed analysis of the solutions' properties is
presented, the domain of existence of the black strings being determined. New
four dimensional solutions are found by boosting the five dimensional
configurations. We also present an argument for the non-existence of finite
mass hyperspherically symmetric black holes in SU(2) Einstein-Yang-Mills
theory.Comment: 19 Revtex pages, 27 eps-figures; discussion on rotating black holes
modifie
Palatini Variational Principle for -Dimensional Dilaton Gravity
We consider a Palatini variation on a general -Dimensional second order,
torsion-free dilaton gravity action and determine the resulting equations of
motion. Consistency is checked by considering the restraint imposed due to
invariance of the matter action under simple coordinate transformations, and
the special case of N=2 is examined. We also examine a sub-class of theories
whereby a Palatini variation dynamically coincides with that of the "ordinary"
Hilbert variational principle; in particular we examine a generalized
Brans-Dicke theory and the associated role of conformal transformations.Comment: 16 pages, LaTe
Rotating Boson Stars and Q-Balls
We consider axially symmetric, rotating boson stars. Their flat space limits
represent spinning Q-balls. We discuss their properties and determine their
domain of existence. Q-balls and boson stars are stationary solutions and exist
only in a limited frequency range. The coupling to gravity gives rise to a
spiral-like frequency dependence of the boson stars. We address the flat space
limit and the limit of strong gravitational coupling. For comparison we also
determine the properties of spherically symmetric Q-balls and boson stars.Comment: 22 pages, 18 figure
A Note on the correspondence between Qubit Quantum Operations and Special Relativity
We exploit a well-known isomorphism between complex hermitian
matrices and , which yields a convenient real vector
representation of qubit states. Because these do not need to be normalized we
find that they map onto a Minkowskian future cone in , whose
vertical cross-sections are nothing but Bloch spheres. Pure states are
represented by light-like vectors, unitary operations correspond to special
orthogonal transforms about the axis of the cone, positive operations
correspond to pure Lorentz boosts. We formalize the equivalence between the
generalized measurement formalism on qubit states and the Lorentz
transformations of special relativity, or more precisely elements of the
restricted Lorentz group together with future-directed null boosts. The note
ends with a discussion of the equivalence and some of its possible
consequences.Comment: 6 pages, revtex, v3: revised discussio
Focusing and the Holographic Hypothesis
The ``screen mapping" introduced by Susskind to implement 't Hooft's
holographic hypothesis is studied. For a single screen time, there are an
infinite number of images of a black hole event horizon, almost all of which
have smaller area on the screen than the horizon area. This is consistent with
the focusing equation because of the existence of focal points. However, the
{\it boundary} of the past (or future) of the screen obeys the area theorem,
and so always gives an expanding map to the screen, as required by the
holographic hypothesis. These considerations are illustrated with several
axisymmetric static black hole spacetimes.Comment: 8 pages, plain latex, 5 figures included using psfi
Averaged Energy Conditions and Evaporating Black Holes
In this paper the averaged weak (AWEC) and averaged null (ANEC) energy
conditions, together with uncertainty principle-type restrictions on negative
energy (``quantum inequalities''), are examined in the context of evaporating
black hole backgrounds in both two and four dimensions. In particular,
integrals over only half-geodesics are studied. We determine the regions of the
spacetime in which the averaged energy conditions are violated. In all cases
where these conditions fail, there appear to be quantum inequalities which
bound the magnitude and extent of the negative energy, and hence the degree of
the violation. The possible relevance of these results for the validity of
singularity theorems in evaporating black hole spacetimes is discussed.Comment: Sections 2.1 and 2.2 have been revised and some erroneous statements
corrected. The main conclusions and the figures are unchanged. 27 pp, plain
Latex, 3 figures available upon reques
Algebraic approach to quantum field theory on non-globally-hyperbolic spacetimes
The mathematical formalism for linear quantum field theory on curved
spacetime depends in an essential way on the assumption of global
hyperbolicity. Physically, what lie at the foundation of any formalism for
quantization in curved spacetime are the canonical commutation relations,
imposed on the field operators evaluated at a global Cauchy surface. In the
algebraic formulation of linear quantum field theory, the canonical commutation
relations are restated in terms of a well-defined symplectic structure on the
space of smooth solutions, and the local field algebra is constructed as the
Weyl algebra associated to this symplectic vector space. When spacetime is not
globally hyperbolic, e.g. when it contains naked singularities or closed
timelike curves, a global Cauchy surface does not exist, and there is no
obvious way to formulate the canonical commutation relations, hence no obvious
way to construct the field algebra. In a paper submitted elsewhere, we report
on a generalization of the algebraic framework for quantum field theory to
arbitrary topological spaces which do not necessarily have a spacetime metric
defined on them at the outset. Taking this generalization as a starting point,
in this paper we give a prescription for constructing the field algebra of a
(massless or massive) Klein-Gordon field on an arbitrary background spacetime.
When spacetime is globally hyperbolic, the theory defined by our construction
coincides with the ordinary Klein-Gordon field theory on aComment: 21 pages, UCSBTH-92-4
Continuous Hawking-Page transitions in Einstein-scalar gravity
We investigate continuous Hawking-Page transitions in Einstein's gravity
coupled to a scalar field with an arbitrary potential in the weak gravity
limit. We show that this is only possible in a singular limit where the
black-hole horizon marginally traps a curvature singularity. Depending on the
subleading terms in the potential, a rich variety of continuous phase
transitions arise. Our examples include second and higher order, including the
Berezinskii-Kosterlitz-Thouless type. In the case when the scalar is dilaton,
the condition for a continuous phase transition lead to (asymptotically)
linear-dilaton background. We obtain the scaling laws of thermodynamic
functions, as well as the viscosity coefficients near the transition. In the
limit of weak gravitational interactions, the bulk viscosity asymptotes to a
universal constant, independent of the details of the scalar potential. As a
byproduct of our analysis we obtain a one-parameter family of kink solutions in
arbitrary dimension d that interpolate between AdS near the boundary and
linear-dilaton background in the deep interior. The continuous Hawking-Page
transitions found here serve as holographic models for normal-to superfluid
transitions.Comment: 35 pages + appendice
Stress-energy tensor in the Bel-Szekeres space-time
In a recent work an approximation procedure was introduced to calculate the
vacuum expectation value of the stress-energy tensor for a conformal massless
scalar field in the classical background determined by a particular colliding
plane wave space-time. This approximation procedure consists in appropriately
modifying the space-time geometry throughout the causal past of the collision
center. This modification in the geometry allows to simplify the boundary
conditions involved in the calculation of the Hadamard function for the quantum
state which represents the vacuum in the flat region before the arrival of the
waves. In the present work this approximation procedure is applied to the
non-singular Bel-Szekeres solution, which describes the head on collision of
two electromagnetic plane waves. It is shown that the stress-energy tensor is
unbounded as the killing-Cauchy horizon of the interaction is approached and
its behavior coincides with a previous calculation in another example of
non-singular colliding plane wave space-time.Comment: 17 pages, LaTex file, 2 PostScript figure
A simple theorem to generate exact black hole solutions
Under certain conditions imposed on the energy-momentum tensor, a theorem
that characterizes a two-parameter family of static and spherically symmetric
solutions to Einstein's field equations (black holes), is proved. A discussion
on the asymptotics, regularity, and the energy conditions is provided. Examples
that include the best known exact solutions within these symmetries are
considered. A trivial extension of the theorem includes the cosmological
constant {\it ab-initio}, providing then a three-parameter family of solutions.Comment: 14 pages; RevTex; no figures; typos corrected; references adde
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