818 research outputs found
Near-horizon geometries of supersymmetric AdS(5) black holes
We provide a classification of near-horizon geometries of supersymmetric,
asymptotically anti-de Sitter, black holes of five-dimensional U(1)^3-gauged
supergravity which admit two rotational symmetries. We find three
possibilities: a topologically spherical horizon, an S^1 \times S^2 horizon and
a toroidal horizon. The near-horizon geometry of the topologically spherical
case turns out to be that of the most general known supersymmetric,
asymptotically anti-de Sitter, black hole of U(1)^3-gauged supergravity. The
other two cases have constant scalars and only exist in particular regions of
this moduli space -- in particular they do not exist within minimal gauged
supergravity. We also find a solution corresponding to the near-horizon
geometry of a three-charge supersymmetric black ring held in equilibrium by a
conical singularity; when lifted to type IIB supergravity this solution can be
made regular, resulting in a discrete family of warped AdS(3) geometries.
Analogous results are presented in U(1)^n gauged supergravity.Comment: Latex, 29 pages. v2: minor improvements, references adde
At the horizon of a supersymmetric AdS_5 black hole: Isometries and half-BPS giants
The near-horizon geometry of an asymptotically AdS_5 supersymmetric black
hole discovered by Gutowski and Reall is analysed. After lifting the solution
to 10 dimensions, we explicitly solve the Killing spinor equations in both
Poincare and global coordinates. It is found that exactly four supersymmetries
are preserved which is twice the number for the full black hole. The full set
of isometries is constructed and the isometry supergroup is shown to be
SU(1,1|1) X SU(2) X U(3). We further study half-BPS configurations of D3-branes
in the near-horizon geometry in Poincare and global coordinates. Both giant
graviton probes and dual giant graviton probes are found.Comment: 26 pages. v2:Typos corrected, minor change
Exchange Interaction in Binuclear Complexes with Rare Earth and Copper Ions: A Many-Body Model Study
We have used a many-body model Hamiltonian to study the nature of the
magnetic ground state of hetero-binuclear complexes involving rare-earth and
copper ions. We have taken into account all diagonal repulsions involving the
rare-earth 4f and 5d orbitals and the copper 3d orbital. Besides, we have
included direct exchange interaction, crystal field splitting of the rare-earth
atomic levels and spin-orbit interaction in the 4f orbitals. We have identified
the inter-orbital repulsion, U and crystal field parameter,
as the key parameters involved in controlling the type of exchange
interaction between the rare earth and copper 3d spins. We have explored
the nature of the ground state in the parameter space of U, ,
spin-orbit interaction strength and the filling n. We find
that these systems show low-spin or high-spin ground state depending on the
filling of the levels of the rare-earth ion and ground state spin is
critically dependent on U and . In case of half-filling
(Gd(III)) we find a reentrant low-spin state as U is increased, for
small values of , which explains the recently reported apparent
anomalous anti-ferromagnetic behaviour of Gd(III)-radical complexes. By varying
U we also observe a switch over in the ground state spin for other
fillings . We have introduced a spin-orbit coupling scheme which goes beyond
L-S or j-j coupling scheme and we find that spin-orbit coupling does not
significantly alter the basic picture.Comment: 22 pages, 11 ps figure
Baryonic Generating Functions
We show how it is possible to use the plethystic program in order to compute
baryonic generating functions that count BPS operators in the chiral ring of
quiver gauge theories living on the world volume of D branes probing a non
compact CY manifold. Special attention is given to the conifold theory and the
orbifold C^2/Z_2 times C, where exact expressions for generating functions are
given in detail. This paper solves a long standing problem for the
combinatorics of quiver gauge theories with baryonic moduli spaces. It opens
the way to a statistical analysis of quiver theories on baryonic branches.
Surprisingly, the baryonic charge turns out to be the quantized Kahler modulus
of the geometry.Comment: 44 pages, 7 figures; fonts change
Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements
Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel
Entropy Function for Non-extremal D1D5 and D2D6NS5-branes
We apply the entropy function formalism to non-extremal D1D5 and
D2D6NS5-branes whose throat approximation is given by the Schwarzschild black
hole in AdS_3\times S^3\times T^4 and AdS_3\times S^2\times S^1\times T^4,
respectively. We find the Bekenstein-Hawking entropy and the (alpha')^3R^4
corrections from the value of the entropy function at its saddle point. While
the higher derivative terms have no effect on the temperature, they decrease
the value of the entropy.Comment: 17 Pages, Latex file; Minor additions, version published in JHE
Extreme air–sea interaction over the North Atlantic subpolar gyre during the winter of 2013–2014 and its sub-surface legacy
Exceptionally low North American temperatures and record-breaking precipitation over the British Isles during winter 2013–2014 were interconnected by anomalous ocean evaporation over the North Atlantic subpolar gyre region (SPG). This evaporation (or oceanic latent heat release) was accompanied by strong sensible heat loss to the atmosphere. The enhanced heat loss over the SPG was caused by a combination of surface westerly winds from the North American continent and northerly winds from the Nordic Seas region that were colder, drier and stronger than normal. A distinctive feature of the air–sea exchange was that the enhanced heat loss spanned the entire width of the SPG, with evaporation anomalies intensifying in the east while sensible heat flux anomalies were slightly stronger upstream in the west. The immediate impact of the strong air–sea fluxes on the ocean–atmosphere system included a reduction in ocean heat content of the SPG and a shift in basin-scale pathways of ocean heat and atmospheric freshwater transport. Atmospheric reanalysis data and the EN4 ocean data set indicate that a longer-term legacy of the winter has been the enhanced formation of a particularly dense mode of Subpolar Mode Water (SPMW)—one of the precursors of North Atlantic Deep Water and thus an important component of the Atlantic Meridional Overturning Circulation. Using particle trajectory analysis, the likely dispersal of newly-formed SPMW is evaluated, providing evidence for the re-emergence of anomalously cold SPMW in early winter 2014/2015
Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture
We consider a cosmological scenario within the KKLT framework for moduli
stabilization in string theory. The universal open string tachyon of decaying
non-BPS D-brane configurations is proposed to drive eternal topological
inflation. Flux-induced `warping' can provide the small slow-roll parameters
needed for successful inflation. Constraints on the parameter space leading to
sufficient number of e-folds, exit from inflation, density perturbations and
stabilization of the Kahler modulus are investigated. The conditions are
difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3
fibrations and other generic Calabi-Yau manifolds. This requires large volume
and magnetic fluxes on the D-brane. The end of inflation may or may not lead to
cosmic strings depending on the original non-BPS configuration. A careful
investigation of initial conditions leading to a phenomenologically viable
model for inflation is carried out. The initial conditions are chosen on the
basis of Sen's open string completeness conjecture. We find time symmetrical
bounce solutions without initial singularities for k=1 FRW models which are
correlated with an inflationary period. Singular big-bang/big-crunch solutions
also exist but do not lead to inflation. There is an intriguing correlation
between having an inflationary universe in 4 dimensions and 6 compact
dimensions or a big-crunch singularity and decompactification.Comment: 43 pages, 9 figures. v3: Typos correcte
Entropy of near-extremal black holes in AdS_5
We construct the microstates of near-extremal black holes in AdS_5 x S^5 as
gases of defects distributed in heavy BPS operators in the dual SU(N)
Yang-Mills theory. These defects describe open strings on spherical D3-branes
in the S^5, and we show that they dominate the entropy by directly enumerating
them and comparing the results with a partition sum calculation. We display new
decoupling limits in which the field theory of the lightest open strings on the
D-branes becomes dual to a near-horizon region of the black hole geometry. In
the single-charge black hole we find evidence for an infrared duality between
SU(N) Yang-Mills theories that exchanges the rank of the gauge group with an
R-charge. In the two-charge case (where pairs of branes intersect on a line),
the decoupled geometry includes an AdS_3 factor with a two-dimensional CFT
dual. The degeneracy in this CFT accounts for the black hole entropy. In the
three-charge case (where triples of branes intersect at a point), the decoupled
geometry contains an AdS_2 factor. Below a certain critical mass, the
two-charge system displays solutions with naked timelike singularities even
though they do not violate a BPS bound. We suggest a string theoretic
resolution of these singularities.Comment: LaTeX; v2: references and a few additional comments adde
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