22,626 research outputs found
On D0-branes in Gepner models
We show why and when D0-branes at the Gepner point of Calabi-Yau manifolds
given as Fermat hypersurfaces exist.Comment: 22 pages, substantial improvements in sections 2 and 3, references
added, version to be publishe
Drinfeld-Manin Instanton and Its Noncommutative Generalization
The Drinfeld-Manin construction of U(N) instanton is reformulated in the ADHM
formulism, which gives explicit general solutions of the ADHM constraints for
U(N) (N>=2k-1) k-instantons. For the N<2k-1 case, implicit results are given
systematically as further constraints, which can be used to the collective
coordinate integral. We find that this formulism can be easily generalized to
the noncommutative case, where the explicit solutions are as well obtained.Comment: 17 pages, LaTeX, references added, mailing address added,
clarifications adde
Stability and BPS branes
We define the concept of Pi-stability, a generalization of mu-stability of
vector bundles, and argue that it characterizes N=1 supersymmetric brane
configurations and BPS states in very general string theory compactifications
with N=2 supersymmetry in four dimensions.Comment: harvmac, 18 p
Fractional Branes in Non-compact Type IIA Orientifolds
We study fractional D-branes in the Type-IIA theory on a non-compact
orientifold of the orbifold C^3/Z_3 in the boundary state formalism. We find
that the fractional D0-branes of the orbifold theory become unstable due to the
presence of a tachyon, while there is a stable D-instanton whose tachyon gets
projected out. We propose that the D-instanton is obtained after tachyon
condensation. We evidence this by calculating the Whitehead group of the
Abelian category of objects corresponding to the boundary states as being
isomorphic to Z_2.Comment: 29 pages, Latex2e minor corrections. references updated. Version
accepted in JHE
A Point's Point of View of Stringy Geometry
The notion of a "point" is essential to describe the topology of spacetime.
Despite this, a point probably does not play a particularly distinguished role
in any intrinsic formulation of string theory. We discuss one way to try to
determine the notion of a point from a worldsheet point of view. The derived
category description of D-branes is the key tool. The case of a flop is
analyzed and Pi-stability in this context is tied in to some ideas of
Bridgeland. Monodromy associated to the flop is also computed via Pi-stability
and shown to be consistent with previous conjectures.Comment: 15 pages, 3 figures, ref adde
Quantum many-body models with cold atoms coupled to photonic crystals
Using cold atoms to simulate strongly interacting quantum systems represents
an exciting frontier of physics. However, as atoms are nominally neutral point
particles, this limits the types of interactions that can be produced. We
propose to use the powerful new platform of cold atoms trapped near
nanophotonic systems to extend these limits, enabling a novel quantum material
in which atomic spin degrees of freedom, motion, and photons strongly couple
over long distances. In this system, an atom trapped near a photonic crystal
seeds a localized, tunable cavity mode around the atomic position. We find that
this effective cavity facilitates interactions with other atoms within the
cavity length, in a way that can be made robust against realistic
imperfections. Finally, we show that such phenomena should be accessible using
one-dimensional photonic crystal waveguides in which coupling to atoms has
already been experimentally demonstrated
The Breakdown of Topology at Small Scales
We discuss how a topology (the Zariski topology) on a space can appear to
break down at small distances due to D-brane decay. The mechanism proposed
coincides perfectly with the phase picture of Calabi-Yau moduli spaces. The
topology breaks down as one approaches non-geometric phases. This picture is
not without its limitations, which are also discussed.Comment: 12 pages, 2 figure
Meta-Stable Dynamical Supersymmetry Breaking Near Points of Enhanced Symmetry
We show that metastable supersymmetry breaking is generic near certain
enhanced symmetry points of gauge theory moduli spaces. Our model consists of
two sectors coupled by a singlet and combines dynamical supersymmetry breaking
with an O'Raifeartaigh mechanism in terms of confined variables. All relevant
mass parameters, including the supersymmetry breaking scale, are generated
dynamically. The metastable vacua appear as a result of a balance between
non-perturbative and perturbative quantum effects along a pseudo-runaway
direction.Comment: 27 pages, harvmac, 6 figure
Dibaryons from Exceptional Collections
We discuss aspects of the dictionary between brane configurations in del
Pezzo geometries and dibaryons in the dual superconformal quiver gauge
theories. The basis of fractional branes defining the quiver theory at the
singularity has a K-theoretic dual exceptional collection of bundles which can
be used to read off the spectrum of dibaryons in the weakly curved dual
geometry. Our prescription identifies the R-charge R and all baryonic U(1)
charges Q_I with divisors in the del Pezzo surface without any Weyl group
ambiguity. As one application of the correspondence, we identify the cubic
anomaly tr R Q_I Q_J as an intersection product for dibaryon charges in large-N
superconformal gauge theories. Examples can be given for all del Pezzo surfaces
using three- and four-block exceptional collections. Markov-type equations
enforce consistency among anomaly equations for three-block collections.Comment: 47 pages, 11 figures, corrected ref
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