217 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
Hairy black holes, scalar charges and extended thermodynamics
We explore the use of the recently defined scalar charge which satisfies a
Gauss law in stationary spacetimes, in the context of theories with a scalar
potential. We find new conditions that this potential has to satisfy in order
to allow for static, asymptotically-flat black-hole solutions with regular
horizons and non-trivial scalar field. These conditions are equivalent to some
of the known ``no-hair'' theorems (such as Bekenstein's). We study the extended
thermodynamics of these systems, deriving a first law and a Smarr formula. As
an example, we study the Anabal\'on-Oliva hairy black holeComment: author name correcte
A note on simple applications of the Killing Spinor Identities
We show how the Killing Spinor Identities (KSI) can be used to reduce the
number of independent equations of motion that need to be checked explicitly to
make sure that a supersymmetric configuration is a classical supergravity
solution. We also show how the KSI can be used to compute BPS relations between
masses and charges.Comment: 10 pages, latex2e. Comments and references added. Version to be
published in Physics Letters
A Note on the D-2-Brane of the Massive Type IIA Theory and Gauged Sigma Models
Gauging the M-2-brane effective action with respect to an Abelian isometry in
such a way that the invariance under gauge transformations of the 3-form
potential is maintained (slightly modified) we obtain a fully covariant action
with 11-dimensional target space that gives the massive D-2-brane effective
action upon dimensional reduction in the direction of the gauged isometry.Comment: Latex file. A reference adde
Supersymmetry as a Cosmic Censor
In supersymmetric theories the mass of any state is bounded below by the
values of some of its charges. The corresponding bounds in case of
Schwarzschild and Reissner-Nordstr\"om black holes are known to coincide with
the requirement that naked singularities be absent. Here we investigate charged
dilaton black holes in this context. We show that the extreme solutions
saturate the supersymmetry bound of supergravity, or dimensionally
reduced superstring theory. Specifically, we have shown that extreme dilaton
black holes, with electric and magnetic charges, admit super-covariantly
constant spinors. The supersymmetric positivity bound for dilaton black holes,
, takes care of the absence of naked
singularities of the dilaton black holes and is, in this sense, equivalent to
the cosmic censorship condition. The temperature, entropy and singularity are
discussed. The Euclidean action (entropy) of the extreme black hole is given by
. We argue that this result, as well as the one for Lorentzian
signature, is not altered by higher order corrections in the supersymmetric
theory. When a black hole reaches its extreme limit, it cannot continue to
evaporate by emitting elementary particles, since this would violate the
supersymmetric positivity bound. We speculate on the possibility that an
extreme black hole may ``evaporate" by emitting smaller extreme black holes.Comment: 42 pages (figures not included
Singular limits of spacetimes and their isometries
We consider spacetime metrics with a given (but quite generic) dependence on
a dimensionful parameter such that in the 0 and infinity limits of that
parameter the metric becomes singular. We study the isometry groups of the
original spacetime metrics and of the singular metrics that arise in the limits
and the corresponding symmetries of the motion of p-branes evolving in them,
showing how the Killing vectors and their Lie algebras can be found in general.
We illustrate our general results with several examples which include limits of
anti-de Sitter spacetime in which the holographic screen is one of the singular
metrics and of pp-waves.Comment: Latex2e paper, 48 page
Black hole chemistry, the cosmological constant and the embedding tensor
We study black-hole thermodynamics in theories that contain dimensionful
constants such as the cosmological constant or coupling constants in Wald's
formalism. The most natural way to deal with these constants is to promote them
to scalar fields introducing a (d-1)-form Lagrange multiplier that forces them
to be constant on-shell. These (d-1)-form potentials provide a dual description
of them and, in the context of superstring/supergravity theories, a
higher-dimensional origin/explanation. In the context of gauged supergravity
theories, all these constants can be collected in the embedding tensor. We show
in an explicit 4-dimensional example that the embedding tensor can also be
understood as a thermodynamical variable that occurs in the Smarr formula in a
duality-invariant fashion. This establishes an interesting link between
black-hole thermodynamics, gaugings and compactifications in the context of
superstring/supergravity theories.Comment: References added, 43 pages, no figure
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
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