7,810 research outputs found
Attractor Flows from Defect Lines
Deforming a two dimensional conformal field theory on one side of a trivial
defect line gives rise to a defect separating the original theory from its
deformation. The Casimir force between these defects and other defect lines or
boundaries is used to construct flows on bulk moduli spaces of CFTs. It turns
out, that these flows are constant reparametrizations of gradient flows of the
g-functions of the chosen defect or boundary condition. The special flows
associated to supersymmetric boundary conditions in N=(2,2) superconformal
field theories agree with the attractor flows studied in the context of black
holes in N=2 supergravity.Comment: 28 page
Permutation branes and linear matrix factorisations
All the known rational boundary states for Gepner models can be regarded as
permutation branes. On general grounds, one expects that topological branes in
Gepner models can be encoded as matrix factorisations of the corresponding
Landau-Ginzburg potentials. In this paper we identify the matrix factorisations
associated to arbitrary B-type permutation branes.Comment: 43 pages. v2: References adde
D-brane superpotentials and RG flows on the quintic
The behaviour of D2-branes on the quintic under complex structure
deformations is analysed by combining Landau-Ginzburg techniques with methods
from conformal field theory. It is shown that the boundary renormalisation
group flow induced by the bulk deformations is realised as a gradient flow of
the effective space time superpotential which is calculated explicitly to all
orders in the boundary coupling constant.Comment: 24 pages, 1 figure, v2:Typo in (3.14) correcte
Moduli Webs and Superpotentials for Five-Branes
We investigate the one-parameter Calabi-Yau models and identify families of
D5-branes which are associated to lines embedded in these manifolds. The moduli
spaces are given by sets of Riemann curves, which form a web whose intersection
points are described by permutation branes. We arrive at a geometric
interpretation for bulk-boundary correlators as holomorphic differentials on
the moduli space and use this to compute effective open-closed superpotentials
to all orders in the open string couplings. The fixed points of D5-brane moduli
under bulk deformations are determined.Comment: 41 pages, 1 figur
A quantum McKay correspondence for fractional 2p-branes on LG orbifolds
We study fractional 2p-branes and their intersection numbers in non-compact
orbifolds as well the continuation of these objects in Kahler moduli space to
coherent sheaves in the corresponding smooth non-compact Calabi-Yau manifolds.
We show that the restriction of these objects to compact Calabi-Yau
hypersurfaces gives the new fractional branes in LG orbifolds constructed by
Ashok et. al. in hep-th/0401135. We thus demonstrate the equivalence of the
B-type branes corresponding to linear boundary conditions in LG orbifolds,
originally constructed in hep-th/9907131, to a subset of those constructed in
LG orbifolds using boundary fermions and matrix factorization of the
world-sheet superpotential. The relationship between the coherent sheaves
corresponding to the fractional two-branes leads to a generalization of the
McKay correspondence that we call the quantum McKay correspondence due to a
close parallel with the construction of branes on non-supersymmetric orbifolds.
We also provide evidence that the boundary states associated to these branes in
a conformal field theory description corresponds to a sub-class of the boundary
states associated to the permutation branes in the Gepner model associated with
the LG orbifold.Comment: LaTeX2e, 1+39 pages, 3 figures (v2) refs added, typos and report no.
correcte
Colloidal ionic complexes on periodic substrates: ground state configurations and pattern switching
We theoretically and numerically studied ordering of "colloidal ionic
clusters" on periodic substrate potentials as those generated by optical
trapping. Each cluster consists of three charged spherical colloids: two
negatively and one positively charged. The substrate is a square or rectangular
array of traps, each confining one such cluster. By varying the lattice
constant from large to small, the observed clusters are first rod-like and form
ferro- and antiferro-like phases, then they bend into a banana-like shape and
finally condense into a percolated structure. Remarkably, in a broad parameter
range between single-cluster and percolated structures, we have found stable
supercomplexes composed of six colloids forming grape-like or rocket-like
structures. We investigated the possibility of macroscopic pattern switching by
applying external electrical fields.Comment: 14 pages, 13 figure
Direct measurement of superluminal group velocity and of signal velocity in an optical fiber
We present an easy way of observing superluminal group velocities using a
birefringent optical fiber and other standard devices. In the theoretical
analysis, we show that the optical properties of the setup can be described
using the notion of "weak value". The experiment shows that the group velocity
can indeed exceed c in the fiber; and we report the first direct observation of
the so-called "signal velocity", the speed at which information propagates and
that cannot exceed c.Comment: 5 pages, 5 figure
Integrability of the N=2 boundary sine-Gordon model
We construct a boundary Lagrangian for the N=2 supersymmetric sine-Gordon
model which preserves (B-type) supersymmetry and integrability to all orders in
the bulk coupling constant g. The supersymmetry constraint is expressed in
terms of matrix factorisations.Comment: LaTeX, 19 pages, no figures; v2: title changed, minor improvements,
refs added, to appear in J. Phys. A: Math. Ge
The matrix factorisations of the D-model
The fundamental matrix factorisations of the D-model superpotential are found
and identified with the boundary states of the corresponding conformal field
theory. The analysis is performed for both GSO-projections. We also comment on
the relation of this analysis to the theory of surface singularities and their
orbifold description.Comment: 23 pages, LaTe
On Upward Drawings of Trees on a Given Grid
Computing a minimum-area planar straight-line drawing of a graph is known to
be NP-hard for planar graphs, even when restricted to outerplanar graphs.
However, the complexity question is open for trees. Only a few hardness results
are known for straight-line drawings of trees under various restrictions such
as edge length or slope constraints. On the other hand, there exist
polynomial-time algorithms for computing minimum-width (resp., minimum-height)
upward drawings of trees, where the height (resp., width) is unbounded.
In this paper we take a major step in understanding the complexity of the
area minimization problem for strictly-upward drawings of trees, which is one
of the most common styles for drawing rooted trees. We prove that given a
rooted tree and a grid, it is NP-hard to decide whether
admits a strictly-upward (unordered) drawing in the given grid.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
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