269 research outputs found
Lensing in an interior Kottler solution
We derive the interior Kottler solution of the incompressible fluid and show
that the bending of light in this solution does depend on the cosmological
constant.Comment: The inner Kottler solution derived and used in this paper is not new.
Corresponding references to Stuchlik (2000) and Boehmer (2003) are added.
Also added: a numerical example and a figure. This is the version accepted by
Gen. Rel. Grav. However it includes a short passage that an anonymous referee
had me suppress
From AdS Black Holes to Supersymmetric Flux-branes
We show that AdS black hole solutions admit an analytical continuation to
become magnetic flux-branes. Although a BPS AdS black hole generally has a
naked singularity, the BPS flux-brane can be regular everywhere with an
appropriate choice of U(1)-charges. This flux-brane interpolates from AdS_{D-2}
\times H^2 at small distance to an asymptotic AdS_D-type metric with an
AdS_{D-2}\times S^1 boundary. We also obtain a smooth cosmological solution of
de Sitter Einstein-Maxwell gravity which flows from dS_2\times S^{D-2} in the
infinite past to a dS_D-type metric, with an S^{D-2}\times S^1 boundary, in the
infinite future.Comment: Plain latex, 25 pages, references adde
Born-Infeld Theory and Stringy Causality
Fluctuations around a non-trivial solution of Born-Infeld theory have a
limiting speed given not by the Einstein metric but the Boillat metric. The
Boillat metric is S-duality invariant and conformal to the open string metric.
It also governs the propagation of scalars and spinors in Born-Infeld theory.
We discuss the potential clash between causality determined by the closed
string and open string light cones and find that the latter never lie outside
the former. Both cones touch along the principal null directions of the
background Born-Infeld field. We consider black hole solutions in situations in
which the distinction between bulk and brane is not sharp such as space filling
branes and find that the location of the event horizon and the thermodynamic
properties do not depend on whether one uses the closed or open string metric.
Analogous statements hold in the more general context of non-linear
electrodynamics or effective quantum-corrected metrics. We show how Born-Infeld
action to second order might be obtained from higher-curvature gravity in
Kaluza-Klein theory. Finally we point out some intriguing analogies with
Einstein-Schr\"odinger theory.Comment: 31 pages, 4 figures, LaTex; Some comments and references adde
Phenomenological implications of light stop and higgsinos
We examine the phenomenological implications of light and
higgsinos in the Minimal Supersymmetric Standard Model, assuming and heavy and gauginos. In this simplified setting,
we study the contributions to , , , , , and their interplay.Comment: plain LATEX, 6 figures, 23 A4 page
Resolution of Overlapping Branes
We obtain singularity resolutions for various overlapping brane
configurations, including those of two heterotic 5-branes, type II 5-branes or
D4-branes. In these solutions, the ``harmonic'' function H for each brane
component depends only on the associated four-dimensional relative transverse
space. The resolution is achieved by replacing these transverse spaces with
Eguchi-Hanson or Taub-NUT spaces, both of which admit a normalisable self-dual
(or anti-self-dual) harmonic 2-form. Due to the manner in which the interaction
terms for the form fields modify their Bianchi identities or equations of
motion, these normalisable harmonic 2-forms provide regular sources for the
branes. We also obtain resolved 5-branes and D4-branes wrapped on S^1, which is
fibred over the transverse Eguchi-Hanson or Taub-NUT spaces. The T-duality
invariance of the NS-NS 5-brane is retained after the resolution. The resolved
5-branes and D4-branes provide regular supergravity duals of certain
supersymmetric Yang-Mills theories in five and four dimensions.Comment: Latex, 13 pages, typo corrected, references added, resolved D4-brane
wrapped on S^1 adde
Twistor geometry of a pair of second order ODEs
We discuss the twistor correspondence between path geometries in three
dimensions with vanishing Wilczynski invariants and anti-self-dual conformal
structures of signature . We show how to reconstruct a system of ODEs
with vanishing invariants for a given conformal structure, highlighting the
Ricci-flat case in particular. Using this framework, we give a new derivation
of the Wilczynski invariants for a system of ODEs whose solution space is
endowed with a conformal structure. We explain how to reconstruct the conformal
structure directly from the integral curves, and present new examples of
systems of ODEs with point symmetry algebra of dimension four and greater which
give rise to anti--self--dual structures with conformal symmetry algebra of the
same dimension. Some of these examples are analogues of plane wave
space--times in General Relativity. Finally we discuss a variational principle
for twistor curves arising from the Finsler structures with scalar flag
curvature.Comment: Final version to appear in the Communications in Mathematical
Physics. The procedure of recovering a system of torsion-fee ODEs from the
heavenly equation has been clarified. The proof of Prop 7.1 has been
expanded. Dedicated to Mike Eastwood on the occasion of his 60th birthda
Ultrarelativistic black hole in an external electromagnetic field and gravitational waves in the Melvin universe
We investigate the ultrarelativistic boost of a Schwarzschild black hole
immersed in an external electromagnetic field, described by an exact solution
of the Einstein-Maxwell equations found by Ernst (the ``Schwarzschild-Melvin''
metric). Following the classical method of Aichelburg and Sexl, the
gravitational field generated by a black hole moving ``with the speed of
light'' and the transformed electromagnetic field are determined. The
corresponding exact solution describes an impulsive gravitational wave
propagating in the static, cylindrically symmetric, electrovac universe of
Melvin, and for a vanishing electromagnetic field it reduces to the well known
Aichelburg-Sexl pp-wave. In the boosting process, the original Petrov type I of
the Schwarzschild-Melvin solution simplifies to the type II on the impulse, and
to the type D elsewhere. The geometry of the wave front is studied, in
particular its non-constant Gauss curvature. In addition, a more general class
of impulsive waves in the Melvin universe is constructed by means of a
six-dimensional embedding formalism adapted to the background. A coordinate
system is also presented in which all the impulsive metrics take a continuous
form. Finally, it is shown that these solutions are a limiting case of a family
of exact gravitational waves with an arbitrary profile. This family is
identified with a solution previously found by Garfinkle and Melvin. We thus
complement their analysis, in particular demonstrating that such spacetimes are
of type II and belong to the Kundt class.Comment: 11 pages, REVTeX
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