227 research outputs found
Supersymmetric probes on the conifold
We study the supersymmetric embeddings of different D-brane probes in the
AdS_5 x T^{1,1} geometry. The main tool employed is kappa symmetry and the
cases studied include D3-, D5- and D7-branes. We find a family of three-cycles
of the T^{1,1} space over which a D3-brane can be wrapped supersymmetrically
and we determine the field content of the corresponding gauge theory duals.
Supersymmetric configurations of D5-branes wrapping a two-cycle and of
spacetime filling D7-branes are also found. The configurations in which the
entire T^{1,1} space is wrapped by a D5-brane (baryon vertex) and a D7-brane
are also studied. Some other embeddings which break supersymmetry but are
nevertheless stable are also determined.Comment: 44 pages, LaTeX; v2: typos corrected, references added, discussion of
D5-brane embeddings improve
Hobby Lobby, Birth Control and Our Ongoing Cultural Wars: Pleasure and Desire in the Crossfires
On Smooth Time-Dependent Orbifolds and Null Singularities
We study string theory on a non-singular time-dependent orbifold of flat
space, known as the `null-brane'. The orbifold group, which involves only
space-like identifications, is obtained by a combined action of a null Lorentz
transformation and a constant shift in an extra direction. In the limit where
the shift goes to zero, the geometry of this orbifold reproduces an orbifold
with a light-like singularity, which was recently studied by Liu, Moore and
Seiberg (hep-th/0204168). We find that the backreaction on the geometry due to
a test particle can be made arbitrarily small, and that there are scattering
processes which can be studied in the approximation of a constant background.
We quantize strings on this orbifold and calculate the torus partition
function. We construct a basis of states on the smooth orbifold whose tree
level string interactions are nonsingular. We discuss the existence of physical
modes in the singular orbifold which resolve the singularity. We also describe
another way of making the singular orbifold smooth which involves a sandwich
pp-wave.Comment: 24 pages, one figur
Noncomparabilities & Non Standard Logics
Many normative theories set forth in the welfare economics, distributive justice and cognate literatures posit noncomparabilities or incommensurabilities between magnitudes of various kinds. In some cases these gaps are predicated on metaphysical claims, in others upon epistemic claims, and in still others upon political-moral claims. I show that in all such cases they are best given formal expression in nonstandard logics that reject bivalence, excluded middle, or both. I do so by reference to an illustrative case study: a contradiction known to beset John Rawls\u27s selection and characterization of primary goods as the proper distribuendum in any distributively just society. The contradiction is avoided only by reformulating Rawls\u27s claims in a nonstandard form, which form happens also to cohere quite attractively with Rawls\u27s intuitive argumentation on behalf of his claims
Higher-Dimensional Black Holes: Hidden Symmetries and Separation of Variables
In this paper, we discuss hidden symmetries in rotating black hole
spacetimes. We start with an extended introduction which mainly summarizes
results on hidden symmetries in four dimensions and introduces Killing and
Killing-Yano tensors, objects responsible for hidden symmetries. We also
demonstrate how starting with a principal CKY tensor (that is a closed
non-degenerate conformal Killing-Yano 2-form) in 4D flat spacetime one can
"generate" 4D Kerr-NUT-(A)dS solution and its hidden symmetries. After this we
consider higher-dimensional Kerr-NUT-(A)dS metrics and demonstrate that they
possess a principal CKY tensor which allows one to generate the whole tower of
Killing-Yano and Killing tensors. These symmetries imply complete integrability
of geodesic equations and complete separation of variables for the
Hamilton-Jacobi, Klein-Gordon, and Dirac equations in the general
Kerr-NUT-(A)dS metrics.Comment: 33 pages, no figures, updated references and corrected typo
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