2,949 research outputs found
Calibrations, Monopoles and Fuzzy Funnels
We present new non-Abelian solitonic configurations in the low energy
effective theory describing a collection of N parallel D1--branes. These
configurations preserve 1/4, 1/8, 1/16 and 1/32 of the spacetime supersymmetry.
They are solutions to a set of generalised Nahm's equations which are related
to self-duality equations in eight dimensions. Our solutions represent
D1--branes which expand into fuzzy funnel configurations ending on collections
of intersecting D3--branes. Supersymmetry dictates that such intersecting
D3--branes must lie on a calibrated three-surface of spacetime and we argue
that the generalised Nahm's equations encode the data for the construction of
magnetic monopoles on the relevant three-surfaces.Comment: 19 pages. Latex. v2: added references and acknowledgmen
Exotic Scalar States in the AdS/CFT Correspondence
We investigate a family of solutions of Type IIb supergravity which
asymptotically approach AdS_5 X S^5 but contain a non-constant dilaton and
volume scalar for the five-sphere. These solutions preserve an SO(1,3) X SO(6)
symmetry. We discuss the solution in the context of the AdS/CFT correspondence,
and we find that as well as running coupling from the nontrivial dilaton, the
corresponding field theory has no supersymmetry and displays confinement at
least for a certain range of parameters.Comment: 18 pages. 3 figures. Revised discussion section, added references.
Final version to appear in JHE
Spin-Two Glueballs, Positive Energy Theorems and the AdS/CFT Correspondence
We determine the spectrum of graviton excitations in the background geometry
of the AdS soliton in p+2 dimensions. Via the AdS/CFT correspondence this
corresponds to determining the spectrum of spin two excitations in the dual
effective p-dimensional field theories For the cases of D3- and M5-branes these
are the spin two glueballs of QCD_3 and QCD_4 respectively. For all values of p
we find an exact degeneracy of the spectra of these tensor states and certain
scalar excitations. Our results also extend the perturbative proof of a
positive energy conjecture for asymptotically locally AdS spacetimes
(originally proposed for p=3) to an arbritrary number of dimensions.Comment: 25 pages, 3 figure
The Free Energy of N=4 Super-Yang-Mills and the AdS/CFT Correspondence
We compute the high-temperature limit of the free energy for four-dimensional
N=4 supersymmetric SU(N_c) Yang-Mills theory. At weak coupling we do so for a
general ultrastatic background spacetime, and in the presence of slowly-varying
background gauge fields. Using Maldacena's conjectured duality, we calculate
the strong-coupling large-N_c expression for the special case that the
three-space has constant curvature. We compare the two results paying
particular attention to curvature corrections to the leading order expressions.Comment: 26 pages.Minor corrections to eqs.(19),(21). Results and conclusions
unchanged. References adde
Fractional Branes and the Entropy of 4D Black Holes
We reconsider the four dimensional extremal black hole constructed in type
IIB string theory as the bound state of D1-branes, D5-branes, momentum, and
Kaluza-Klein monopoles. Specifically, we examine the case of an arbitrary
number of monopoles. Consequently, the weak coupling calculation of the
microscopic entropy requires a study of the D1-D5 system on an ALE space. We
find that the complete expression for the Bekenstein-Hawking entropy is
obtained by taking into account the massless open strings stretched between the
fractional D-branes which arise in the orbifold limit of the ALE space. The
black hole sector therefore arises as a mixed Higgs-Coulomb branch of an
effective 1+1 dimensional gauge theory.Comment: 12 pages. 1 figure. v2: References adde
Statistics of the geomagnetic secular variation for the past 5Ma
A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions
Non-abelian instantons on a fuzzy four-sphere
We study the compatibility between the instanton and the fuzzy
four-sphere algebra. By using the projective module point of view as an
intermediate step, we are able to identify a non-commutative solution of the
matrix model equations of motion which minimally extends the SU(2) instanton
solution on the classical sphere . We also propose to extend the
non-trivial second Chern class with the five-dimensional noncommutative
Chern-Simons term
Intersecting Branes, Defect Conformal Field Theories and Tensionless Strings
The defect conformal field theory describing intersecting D3-branes at a
C^2/Z_k orbifold is used to (de)construct the theory of intersecting M5-branes,
as well as M5-branes wrapping the holomorphic curve xy=c. The possibility of a
't Hooft anomaly due to tensionless strings at the intersection is discussed.
This note is based on a talk given by Zachary Guralnik at the 35th
International Symposium Ahrenshoop on the Theory of Elementary Particles.Comment: latex, one figure, 9pages. Talk given by Z.G. at the 35th
International Symposium Ahrenshoop on the Theory of Elementary Particle
Education for social work as a self-regulating profession
The paper was given on 5 April 2000 as an invitational paper
at the university of Macerata in Italy upon the opening of
their new program preparing for social work (assistence
sociale) practice in Italy. The paper discusses models of social
work education which would prepare for free-standing,
self-regulated practice (una libera professione) of social
work, similar to professions of physicians, lawyers, accountants,
etc. there is discussion of international models
of social work practice, the general scope of work an advanced,
specialized practice
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