298 research outputs found
A note on the hidden conformal structure of non-extremal black holes
We study, following Bertini et al. \cite{Bertini:2011ga}, the hidden
conformal symmetry of the massless Klein-Gordon equation in the background of
the general, charged, spherically symmetric, static black-hole solution of a
class of d-dimensional Lagrangians which includes the relevant parts of the
bosonic Lagrangian of any ungauged supergravity. We find that a hidden
SL(2,\mathbb{R}) symmetry appears at the near event and Cauchy-horizon limit.Comment: 9 pages. The 2 sl(2) algebras have been extended to two complete Witt
algebras. A discussion has been adde
Massless Black Holes as Black Diholes and Quadruholes
Massless black holes can be understood as bound states of a (positive mass)
extreme a=\sqrt{3} black hole and a singular object with opposite (i.e.
negative) mass with vanishing ADM (total) mass but non-vanishing gravitational
field. Supersymmetric balance of forces is crucial for the existence of this
kind of bound states and explains why the system does not move at the speed of
light. We also explain how supersymmetry allows for negative mass as long as it
is never isolated but in bound states of total non-negative mass.Comment: Version to be published in Physical Review Letters. Latex2e fil
The Internal Spin Angular Momentum of an Asymptotically Flat Spacetime
In this paper we investigate the manner in which the internal spin angular
momentum of a spinor field is encoded in the gravitational field at asymptotic
infinity. The inclusion of internal spin requires us to re-analyze our notion
of asymptotic flatness. In particular, the Poincar\'{e} symmetry at asymptotic
infinity must replaced by a spin-enlarged Poincar\'{e} symmetry. Likewise, the
generators of the asymptotic symmetry group must be supplemented to account for
the internal spin. In the Hamiltonian framework of first order Einstein-Cartan
gravity, the extra generator comes from the boundary term of the Gauss
constraint in the asymptotically flat context. With the additional term, we
establish the relations among the Noether charges of a Dirac field, the Komar
integral, and the asymptotic ADM-like geometric integral. We show that by
imposing mild restraints on the generating functionals of gauge transformations
at asymptotic infinity, the phase space is rendered explicitly finite. We
construct the energy-momentum and the new total (spin+orbital) angular momentum
boundary integrals that satisfy the appropriate algebra to be the generators of
the spin-enlarged Poincar\'{e} symmetry. This demonstrates that the internal
spin is encoded in the tetrad at asymptotic infinity. In addition, we find that
a new conserved and (spin-enlarged) Poincar\'{e} invariant charge emerges that
is associated with the global structure of a gauge transformation.Comment: V2: No major changes, journal reference adde
The FGK formalism for black p-branes in d dimensions
We present a generalization to an arbitrary number of spacetime (d) and
worldvolume (p+1) dimensions of the formalism proposed by Ferrara, Gibbons and
Kallosh to study black holes (p=0) in d=4 dimensions. We include the special
cases in which there can be dyonic and self- or anti-self-dual black branes.
Most of the results valid for 4-dimensional black holes (relations between
temperature, entropy and non-extremality parameter, and between entropy and
black-hole potential on the horizon) are straightforwardly generalized.
We apply the formalism to the case of black strings in N=2,d=5 supergravity
coupled to vector multiplets, in which the black-string potential can be
expressed in terms of the dual central charge and work out an explicit example
with one vector multiplet, determining supersymmetric and non-supersymmetric
attractors and constructing the non-extremal black-string solutions that
interpolate between them.Comment: 28 pages no figures; v2: some references adde
Geometric Properties of Static EMdL Horizons
We study non-degenerate and degenerate (extremal) Killing horizons of
arbitrary geometry and topology within the Einstein-Maxwell-dilaton model with
a Liouville potential (the EMdL model) in d-dimensional (d>=4) static
space-times. Using Israel's description of a static space-time, we construct
the EMdL equations and the space-time curvature invariants: the Ricci scalar,
the square of the Ricci tensor, and the Kretschmann scalar. Assuming that
space-time metric functions and the model fields are real analytic functions in
the vicinity of a space-time horizon, we study behavior of the space-time
metric and the fields near the horizon and derive relations between the
space-time curvature invariants calculated on the horizon and geometric
invariants of the horizon surface. The derived relations generalize the similar
relations known for horizons of static four and 5-dimensional vacuum and
4-dimensional electrovacuum space-times. Our analysis shows that all the
extremal horizon surfaces are Einstein spaces. We present necessary conditions
for existence of static extremal horizons within the EMdL model.Comment: 10 page
Torsion cosmological dynamics
In this paper, the dynamical attractor and heteroclinic orbit have been
employed to make the late-time behaviors of the model insensitive to the
initial condition and thus alleviate the fine-tuning problem in the torsion
cosmology. The late-time de Sitter attractor indicates that torsion cosmology
is an elegant scheme and the scalar torsion mode is an interesting geometric
quantity for physics. The numerical solutions obtained by Nester et al. are not
periodic solutions, but are quasi-periodic solutions near the focus for the
coupled nonlinear equations.Comment: 4 pages, 3 figure
Quadratic superconducting cosmic strings revisited
It has been shown that 5-dimensional general relativity action extended by
appropriate quadratic terms admits a singular superconducting cosmic string
solution. We search for cosmic strings endowed with similar and extended
physical properties by directly integrating the non-linear matrix field
equations thus avoiding the perturbative approach by which we constructed the
above-mentioned \textsl{exact} solution. The most general superconducting
cosmic string, subject to some constraints, will be derived and shown to be
mathematically \textsl{unique} up to linear coordinate transformations mixing
its Killing vectors. The most general solution, however, is not globally
equivalent to the old one due to the existence of Killing vectors with closed
orbits.Comment: 6 page
Gravity from a fermionic condensate of a gauge theory
The most prominent realization of gravity as a gauge theory similar to the
gauge theories of the standard model comes from enlarging the gauge group from
the Lorentz group to the de Sitter group. To regain ordinary Einstein-Cartan
gravity the symmetry must be broken, which can be accomplished by known
quasi-dynamic mechanisms. Motivated by symmetry breaking models in particle
physics and condensed matter systems, we propose that the symmetry can
naturally be broken by a homogenous and isotropic fermionic condensate of
ordinary spinors. We demonstrate that the condensate is compatible with the
Einstein-Cartan equations and can be imposed in a fully de Sitter invariant
manner. This lends support, and provides a physically realistic mechanism for
understanding gravity as a gauge theory with a spontaneously broken local de
Sitter symmetry.Comment: 16 page
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