269 research outputs found
The CFT dual of AdS gravity with torsion
We consider the Mielke-Baekler model of three-dimensional AdS gravity with
torsion, which has gravitational and translational Chern-Simons terms in
addition to the usual Einstein-Hilbert action with cosmological constant. It is
shown that the topological nature of the model leads to a finite
Fefferman-Graham expansion. We derive the holographic stress tensor and the
associated Ward identities and show that, due to the asymmetry of the left- and
right-moving central charges, a Lorentz anomaly appears in the dual conformal
field theory. Both the consistent and the covariant Weyl and Lorentz anomaly
are determined, and the Wess-Zumino consistency conditions for the former are
verified. Moreover we consider the most general solution with flat boundary
geometry, which describes left-and right-moving gravitational waves on AdS_3
with torsion, and shew that in this case the holographic energy-momentum tensor
is given by the wave profiles. The anomalous transformation laws of the wave
profiles under diffeomorphisms preserving the asymptotic form of the bulk
solution yield the central charges of the dual CFT and confirm the results that
appeared earlier on in the literature. We finally comment on some points
concerning the microstate counting for the Riemann-Cartan black hole.Comment: 17 pages, uses JHEP3.cls. References added, minor errors correcte
Covariant description of the black hole entropy in 3D gravity
We study the entropy of the black hole with torsion using the covariant form
of the partition function. The regularization of infinities appearing in the
semiclassical calculation is shown to be consistent with the grand canonical
boundary conditions. The correct value for the black hole entropy is obtained
provided the black hole manifold has two boundaries, one at infinity and one at
the horizon. However, one can construct special coordinate systems, in which
the entropy is effectively associated with only one of these boundaries.Comment: 12 pages, LaTeX, v2: new material in section IV clarifies the effects
pertaining to the use of different coordinate system
Black hole entropy in 3D gravity with torsion
The role of torsion in quantum three-dimensional gravity is investigated by
studying the partition function of the Euclidean theory in Riemann-Cartan
spacetime. The entropy of the black hole with torsion is found to differ from
the standard Bekenstein-Hawking result, but its form is in complete agreement
with the first law of black hole thermodynamics.Comment: 17 pages, RevTeX, minor revision
Noncommutative gauge theory using covariant star product defined between Lie-valued differential forms
We develop an internal gauge theory using a covariant star product. The
space-time is a symplectic manifold endowed only with torsion but no curvature.
It is shown that, in order to assure the restrictions imposed by the
associativity property of the star product, the torsion of the space-time has
to be covariant constant. An illustrative example is given and it is concluded
that in this case the conditions necessary to define a covariant star product
on a symplectic manifold completely determine its connection.Comment: AMS-LaTeX 19 pages. v2: corrections in language and equations
(typos), expanded sections 3-5, added references. v3: minor presentational
and grammatical corrections, completed, corrected and reordered some
references
AdS-inspired noncommutative gravity on the Moyal plane
We consider noncommutative gravity on a space with canonical noncommutativity
that is based on the commutative MacDowell-Mansouri action. Gravity is treated
as gauge theory of the noncommutative group and the
Seiberg-Witten (SW) map is used to express noncommutative fields in terms of
the corresponding commutative fields. In the commutative limit the
noncommutative action reduces to the Einstein-Hilbert action plus the
cosmological term and the topological Gauss-Bonnet term. After the SW expansion
in the noncommutative parameter the first order correction to the action, as
expected, vanishes. We calculate the second order correction and write it in a
manifestly gauge covariant way.Comment: 22 pages, no figures, final versio
2D Induced Gravity as an Effective WZNW System
We introduced a dynamical system given by a difference of two simple SL(2,R)
WZNW actions in 2D, and defined the related gauge theory in a consistent way.
It is shown that gauge symmetry can be fixed in such a way that, after
integrating out some dynamical variables in the functional integral, one
obtains the induced gravity action.Comment: LaTeX, 16 page
2D induced gravity from canonically gauged WZNW system
Starting from the Kac--Moody structure of the WZNW model for SL(2,R) and
using the general canonical formalism, we formulate a gauge theory invariant
under local SL(2,R) x SL(2,R) and diffeomorphisms. This theory represents a
gauge extension of the WZNW system, defined by a difference of two simple WZNW
actions. By performing a partial gauge fixing and integrating out some
dynamical variables, we prove that the resulting effective theory coincides
with the induced gravity in 2D. The geometric properties of the induced gravity
are obtained out of the gauge properties of the WZNW system with the help of
the Dirac bracket formalism.Comment: LaTeX, 21 page
A Tverberg type theorem for matroids
Let b(M) denote the maximal number of disjoint bases in a matroid M. It is
shown that if M is a matroid of rank d+1, then for any continuous map f from
the matroidal complex M into the d-dimensional Euclidean space there exist t
\geq \sqrt{b(M)}/4 disjoint independent sets \sigma_1,\ldots,\sigma_t \in M
such that \bigcap_{i=1}^t f(\sigma_i) \neq \emptyset.Comment: This article is due to be published in the collection of papers "A
Journey through Discrete Mathematics. A Tribute to Jiri Matousek" edited by
Martin Loebl, Jaroslav Nesetril and Robin Thomas, due to be published by
Springe
Arterijska vaskularizacija mozga malog zelenog majmuna, Cercopithecus aethiops sabeus
Cell cultures from the small green monkey are used for the cultivation of poliovirus in the manufacture of vaccines against poliomyelitis. In addition kidney cultures from the same monkey serve for detection of the virus in biological material. This was the main reason that prompted us to undertake a study of one part of the monkey’s cardiosvascular system and thus contribute to a better understanding of the structure of its body.Glavni krvni sudovi koji dovode arterijsku krv u mozak su A.carotis interna i A. vertebralis. Spajanjem leve i desne kičmene arterije (A. vertebralis sinistra et dextra) nastaje A. basilaris cerebri. A. carotis interna sinistra et dextra pružaju se kroz parafaringealni prostor prema lobanjskoj duplji, u koju ulaze pošto prođu kroz karotidne kanale (canales carotici) piramide slepoočne kosti u kavernozni sinus u kome se povezuju obe Aa. carotides preko A. intercarotica caudalis. Grane A. carotis internae su: A. ophthalmica, A. cerebri media, A. communicans caudalis. A.ophthalmica dovodi krv u optičke i pomoćne delove oka. A. cerebri media daje grane koje ulaze u moždanu masu i dovodi krv u lateralnu površinu moždane hemisfere. A. communicans caudalis povezuje zadnju moždanu arteriju (A. cerebri caudalis) sa unutrašnjom karotidnom arterijom i daje grane za vaskularizaciju hipotalamusa. A.cerebri rostralis je produžetak stabla unutrašnje karotidne arterije. Ona se spaja sa odgovarajućom granom druge strane ispred Chiasma opticum. Iz ovog spoja nastaje A. cerebri rostralis communis. Od A. cerebri rostralis odvajaju se površne i duboke grane koje ulaze u moždanu masu. A. cerebri caudalis, A. communicans caudalis i A. cerebri rostralis obrazuju oko hipofize i raskršća vidnih nerava arterijski krug (Circulus arteriosus Willisi)
Canonical approach to 2D WZNW model, non-abelian bosonization and anomalies
The gauged WZNW model has been derived as an effective action, whose Poisson
bracket algebra of the constraints is isomorphic to the commutator algebra of
operators in quantized fermionic theory. As a consequence, the hamiltonian as
well as usual lagrangian non-abelian bosonization rules have been obtained, for
the chiral currents and for the chiral densities. The expression for the
anomaly has been obtained as a function of the Schwinger term, using canonical
methods.Comment: RevTex, 23 page
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