299 research outputs found
Kaluza-Klein Consistency, Killing Vectors, and Kahler Spaces
We make a detailed investigation of all spaces Q_{n_1... n_N}^{q_1... q_N} of
the form of U(1) bundles over arbitrary products \prod_i CP^{n_i} of complex
projective spaces, with arbitrary winding numbers q_i over each factor in the
base. Special cases, including Q_{11}^{11} (sometimes known as T^{11}),
Q_{111}^{111} and Q_{21}^{32}, are relevant for compactifications of type IIB
and D=11 supergravity. Remarkable ``conspiracies'' allow consistent
Kaluza-Klein S^5, S^4 and S^7 sphere reductions of these theories that retain
all the Yang-Mills fields of the isometry group in a massless truncation. We
prove that such conspiracies do not occur for the reductions on the Q_{n_1...
n_N}^{q_1... q_N} spaces, and that it is inconsistent to make a massless
truncation in which the non-abelian SU(n_i+1) factors in their isometry groups
are retained. In the course of proving this we derive many properties of the
spaces Q_{n_1... n_N}^{q_1... q_N} of more general utility. In particular, we
show that they always admit Einstein metrics, and that the spaces where
q_i=(n_i+1)/\ell all admit two Killing spinors. We also obtain an iterative
construction for real metrics on CP^n, and construct the Killing vectors on
Q_{n_1... n_N}^{q_1... q_N} in terms of scalar eigenfunctions on CP^{n_i}. We
derive bounds that allow us to prove that certain Killing-vector identities on
spheres, necessary for consistent Kaluza-Klein reductions, are never satisfied
on Q_{n_1... n_N}^{q_1... q_N}.Comment: Latex, 43 pages, references added and typos correcte
Toric G_2 and Spin(7) holonomy spaces from gravitational instantons and other examples
Non-compact G_2 holonomy metrics that arise from a T^2 bundle over a
hyper-Kahler space are discussed. These are one parameter deformations of the
metrics studied by Gibbons, Lu, Pope and Stelle in hep-th/0108191.
Seven-dimensional spaces with G_2 holonomy fibered over the Taub-Nut and the
Eguchi-Hanson gravitational instantons are found, together with other examples.
By considering the Apostolov-Salamon theorem math.DG/0303197, we construct a
new example that, still being a T^2 bundle over hyper-Kahler, represents a non
trivial two parameter deformation of the metrics studied in hep-th/0108191. We
then review the Spin(7) metrics arising from a T^3 bundle over a hyper-Kahler
and we find two parameter deformation of such spaces as well. We show that if
the hyper-Kahler base satisfies certain properties, a non trivial three
parameter deformations is also possible. The relation between these spaces with
the half-flat structures and almost G_2 holonomy spaces is briefly discussed.Comment: 27 pages. Typos corrected. Accepted for publication in
Commun.Math.Phy
A New Fractional D2-brane, G_2 Holonomy and T-duality
Recently, a new example of a complete non-compact Ricci-flat metric of G_2
holonomy was constructed, which has an asymptotically locally conical structure
at infinity with a circular direction whose radius stabilises. In this paper we
find a regular harmonic 3-form in this metric, which we then use in order to
obtain an explicit solution for a fractional D2-brane configuration. By
performing a T-duality transformation on the stabilised circle, we obtain the
type IIB description of the fractional brane, which now corresponds to D3-brane
with one of its world-volume directions wrapped around the circle.Comment: Latex, 13 page
Black hole entropy reveals a 12th "dimension"
The Beckenstein-Hawking black hole entropy in string theory and its
extensions, as expressed in terms of charges that correspond to central
extensions of the supersymmetry algebra, has more symmetries than U-duality. It
is invariant under transformations of the charges, involving a 12th (or 13th)
``dimension''. This is an indication that the secret theory behind string
theory has a superalgebra involving Lorentz non-scalar extensions (that are not
strictly central), as suggested in S-theory, and which could be hidden in M- or
F- theories. It is suggested that the idea of spacetime is broader than usual,
and that a larger ``spacetime" is partially present in black holes.Comment: Latex, 20 pages, minor formatting correction
Curved branes from string dualities
We describe a simple method for generating new string solutions for which the
brane worldvolume is a curved space. As a starting point we use solutions with
NS-NS charges combined with 2-d CFT's representing different parts of
space-time. We illustrate our method with many examples, some of which are
associated with conformally invariant sigma models. Using U-duality, we also
obtain supergravity solutions with RR charges which can be interpreted as
D-branes with non-trivial worldvolume geometry. In particular, we discuss the
case of a D5-brane wrapped on AdS_3 x S^3, a solution interpolating between
AdS_3 x S^3 x R^5 and AdS_3 x S^3 x S^3 x R, and a D3-brane wrapped over S^3 x
R or AdS_2 x S^2. Another class of solutions we discuss involves NS5-branes
intersecting over a 3-space and NS5-branes intersecting over a line. These
solutions are similar to D7-brane or cosmic string backgrounds.Comment: 21 pages, harvmac; misprint correcte
Black hole entropy as T-duality invariant
We study the Euler numbers and the entropies of the non-extremal intersecting
D-branes in ten-dimensions. We use the surface gravity to constrain the
compactification radii. We correctly obtain the integer valued Euler numbers
for these radii. Moreover, the entropies are found to be invariant under the
T-duality transformation. In the extremal limit, we obtain the finite entropies
only for two intersecting D-branes. We observe that these entropies are
proportional to the product of the charges of each D-brane. We further study
the entropies of the boosted metrics. We find that their entropies can be
interpreted in term of the microscopic states of D-branes.Comment: 15 pages, Revte
D0-D4 system and QCD_{3+1}
We consider a -dimensional QCD model using a dual supergravity
description with a non-extremal - brane background. We calculate the
spectrum of glueball masses and Wilson loops in the background. The mass
spectrum is shown to coincide with one in non-extremal -brane systems, and
an area low of spatial Wilson loops is established. We show that there is a
region that Kaluza-Klein modes of the Euclidean time direction are decoupled
without decoupling glueball masses.Comment: 10 pages, REVTeX; typos correcte
Fragmentation of Spinning Branes
The near-horizon geometries of the spinning D3-, M2- and M5-branes are
examined by the probes immersed in a co-rotating frame. It is found that the
geometries become unstable at critical values of the spin angular velocity by
emitting the branes. We show that this instability corresponds to the
metastability of the black hole systems and different from the known (local)
thermodynamic instability. For the D3 case, the instability found here is in
complete agreement with the known metastability of the N=4 super-Yang-Mills
theory with R-symmetry chemical potentials.Comment: 16 pages + appendices; v2 is the published version with no essential
change from v1 but a reference adde
Thermodynamics of Kerr-Newman-AdS Black Holes and Conformal Field Theories
We study the thermodynamics of four-dimensional Kerr-Newman-AdS black holes
both in the canonical and the grand-canonical ensemble. The stability
conditions are investigated, and the complete phase diagrams are obtained,
which include the Hawking-Page phase transition in the grand-canonical
ensemble. In the canonical case, one has a first order transition between small
and large black holes, which disappears for sufficiently large electric charge
or angular momentum. This disappearance corresponds to a critical point in the
phase diagram. Via the AdS/CFT conjecture, the obtained phase structure is also
relevant for the corresponding conformal field theory living in a rotating
Einstein universe, in the presence of a global background U(1) current. An
interesting limit arises when the black holes preserve some supersymmetry.
These BPS black holes correspond to highly degenerate zero temperature states
in the dual CFT, which lives in an Einstein universe rotating with the speed of
light.Comment: 27 pages, RevTeX, 12 ps figures. Minor changes, references added.
Final version to appear in Class. Quantum Gra
Time-dependent backgrounds from supergravity with gauged non-compact R-symmetry
We obtain a general class of time-dependent, asymptotically de Sitter
backgrounds which solve the first order bosonic equations that extremize the
action for supergravity with gauged non-compact -symmetry. These backgrounds
correspond only to neutral fields with the correct sign of kinetic energy.
Within N=2 five-dimensional supergravity with vector-superfields we provide
examples of multi-centered charged black holes in asymptotic de Sitter space,
whose spatial part is given by a time-dependent hyper-K\"ahler space. Reducing
these backgrounds to four dimensions yields asymptotically de Sitter
multi-centered charged black hole backgrounds and we show that they are related
to an instanton configuration by a massive T-duality over time. Within N=2
gauged supergravity in four (and five)-dimensions with hyper-multiplets there
could also be neutral cosmological backgrounds that are regular and correspond
to the different de Sitter spaces at early and late times.Comment: 28 pages, Latex; minor changes and add reference
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