329 research outputs found
SUSY Enhancements in (0,4) Deformations of AdS_3/CFT_2
We discuss a marginal deformation of the SL(2,R) x SU(2) x U(1)^4 WZW model,
which describes string theory on AdS_3 x S^3 x T^4, that corresponds to warping
the S^3 factor. This deformation breaks part of the N=(4,4) supersymmetry of
the undeformed dual CFT to N=(0,4) supersymmetry. In the spirit of work by
Giveon, Kutasov, and Seiberg, we construct the asymptotic spacetime symmetry
algebra from worldsheet operators and find a restoration of (4,4) supersymmetry
at discrete values of the deformation parameter. We explain this result from
various perspectives: the worldsheet, supergravity, and from the singular D1-D5
CFT. The supergravity analysis includes an asymptotic symmetry computation of
the level of the affine SU(2) R-symmetry, which arises purely from B-field
contributions.Comment: 16 pages; v2: references adde
Global geometry of the 2+1 rotating black hole
The generic rotating BTZ black hole, obtained by identifications in AdS3
space through a discrete subgroup of its isometry group, is investigated within
a Lie theoretical context. This space is found to admit a foliation by
two-dimensional leaves, orbits of a two-parameter subgroup of SL(2,R) and
invariant under the BTZ identification subgroup. A global expression for the
metric is derived, allowing a better understanding of the causal structure of
the black hole.Comment: 9 pages, 1 figur
Flat-Space Chiral Gravity
We provide the first evidence for a holographic correspondence between a
gravitational theory in flat space and a specific unitary field theory in one
dimension lower. The gravitational theory is a flat-space limit of
topologically massive gravity in three dimensions at Chern-Simons level k=1.
The field theory is a chiral two-dimensional conformal field theory with
central charge c=24.Comment: 5 pages, v2: minor rearrangement
Holographic Chern-Simons Theories
Chern-Simons theories in three dimensions are topological field theories that
may have a holographic interpretation for suitable chosen gauge groups and
boundary conditions on the fields. Conformal Chern-Simons gravity is a
topological model of 3-dimensional gravity that exhibits Weyl invariance and
allows various holographic descriptions, including Anti-de Sitter, Lobachevsky
and flat space holography. The same model also allows to address some aspects
that arise in higher spin gravity in a considerably simplified setup, since
both types of models have gauge symmetries other than diffeomorphisms. In these
lectures we summarize briefly recent results.Comment: 20 pp, invited lectures prepared for the 7th Aegean Summer School
"Beyond Einstein's Theory of Gravity", 201
Holography of 3d Flat Cosmological Horizons
We provide a first derivation of the Bekenstein-Hawking entropy of 3d flat
cosmological horizons in terms of the counting of states in a dual field
theory. These horizons appear in the shifted-boost orbifold of R^{1,2}, the
flat limit of non-extremal rotating BTZ black holes. These 3d geometries carry
non-zero charges under the asymptotic symmetry algebra of R^{1,2}, the 3d
Bondi-Metzner-Sachs (BMS3) algebra. The dual theory has the symmetries of the
2d Galilean Conformal Algebra, a contraction of two copies of the Virasoro
algebra, which is isomorphic to BMS3. We study flat holography as a limit of
AdS3/CFT2 to semi-classically compute the density of states in the dual,
exactly reproducing the bulk entropy in the limit of large charges. Our flat
horizons, remnants of the BTZ inner horizons also satisfy a first law of
thermodynamics. We comment on how the dual theory reproduces the bulk first law
and how cosmological bulk excitations are matched with boundary quantum
numbers.Comment: 5 pages; v2: Typos corrected, references update
Inner Mechanics of 3d Black Holes
We investigate properties of the inner horizons of certain black holes in
higher-derivative three-dimensional gravity theories. We focus on BTZ and
Spacelike Warped Anti-de Sitter black holes, as well as on asymptotically
Warped de-Sitter solutions exhibiting both a cosmological and a black hole
horizon. We verify that a First Law is satisfied at the Inner horizon, in
agreement with the proposal of \cite{Castro:2012av}. We then show that, in
Topologically Massive Gravity, the product of the areas of the inner and outer
horizons fails to be independent on the mass, and trace this to the
diffeomorphism anomaly of the theory.Comment: 5 page
The Fuzzy Sphere: From The Uncertainty Relation To The Stereographic Projection
On the fuzzy sphere, no state saturates simultaneously all the Heisenberg
uncertainties. We propose a weaker uncertainty for which this holds. The family
of states so obtained is physically motivated because it encodes information
about positions in this fuzzy context. In particular, these states realize in a
natural way a deformation of the stereographic projection. Surprisingly, in the
large limit, they reproduce some properties of the ordinary coherent states
on the non commutative plane.Comment: 18 pages, Latex. Minor changes in notations. Version to appear in
JHE
A study on PDC drill bits quality
The quality of innovating PDC (Polycrystalline Diamond Compact) bits materials needs to be determined with accuracy by measuring cutting efficiency and wear rate, both related to the overall mechanical properties. An original approach is developed to encompass cutting efficiency and wear contribution to the overall sample quality. Therefore, a lathe-type test device was used to abrade specific samples from various manufacturers. Post-experiment analyzes are based on models establishing coupled relationships between cutting and friction stresses related to the drag bits excavation mechanism. These models are implemented in order to evaluate cutting efficiency and to estimate wear of the diamond insert. Phase analysis by XRD and finite element simulations were performed to explain the role of physicochemical parameters on the calculated quality factor values. Four main properties of PDC material were studied to explain quality results obtained in this study: cobalt content in samples that characterizes hardness/fracture toughness compromise, undesired phase as tungsten carbide weakening diamond structure, diamond grains sizes and residual stresses distribution affecting abrasion resistance
Three-dimensional black holes from deformed anti-de Sitter
We present new exact three-dimensional black-string backgrounds, which
contain both NS--NS and electromagnetic fields, and generalize the BTZ black
holes and the black string studied by Horne and Horowitz. They are obtained as
deformations of the Sl(2,R) WZW model. Black holes resulting from purely
continuous deformations possess true curvature singularities. When discrete
identifications are introduced, extra chronological singularities appear, which
under certain circumstances turn out to be naked. The backgrounds at hand
appear in the moduli space of the Sl(2,R) WZW model. Hence, they provide exact
string backgrounds and allow for a more algebraical CFT description. This makes
possible the determination of the spectrum of primaries.Comment: JHEP style, 33 pages, 1 figur
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