1,606 research outputs found
Normal bundles to Laufer rational curves in local Calabi-Yau threefolds
We prove a conjecture by F. Ferrari. Let X be the total space of a nonlinear
deformation of a rank 2 holomorphic vector bundle on a smooth rational curve,
such that X has trivial canonical bundle and has sections. Then the normal
bundle to such sections is computed in terms of the rank of the Hessian of a
suitably defined superpotential at its critical points
Conifold geometries, matrix models and quantum solutions
This paper is a continuation of hepth/0507224 where open topological B-models
describing D-branes on 2-cycles of local Calabi--Yau geometries with conical
singularities were studied. After a short review, the paper expands in
particular on two aspects: the gauge fixing problem in the reduction to two
dimensions and the quantum matrix model solutions.Comment: 17 p. To appear in proc. Symposium QTS-4, Varna (Bulgaria), August
200
Mapping prior information onto LMI eigenvalue-regions for discrete-time subspace identification
In subspace identification, prior information can be used to constrain the
eigenvalues of the estimated state-space model by defining corresponding LMI
regions. In this paper, first we argue on what kind of practical information
can be extracted from historical data or step-response experiments to possibly
improve the dynamical properties of the corresponding model and, also, on how
to mitigate the effect of the uncertainty on such information. For instance,
prior knowledge regarding the overshoot, the period between damped oscillations
and settling time may be useful to constraint the possible locations of the
eigenvalues of the discrete-time model. Then, we show how to map the prior
information onto LMI regions and, when the obtaining regions are non-convex, to
obtain convex approximations.Comment: Under revie
Some comments on the local curve (B-side)
We consider non-compact Calabi-Yau threefolds that are fibrations over
compact Riemann surfaces, the local curves, and study the dynamics of B-branes
wrapped around the curves. We discuss different but closely related possible
approaches to this problem. In particular, we study the open topological string
field theory of the B-brane and the dimensional reduction of the holomorphic
Chern-Simons functional to the curve. The classical (g_s = 0) limit of these
dynamics for one single brane is given by the deformation theory of the curve
inside the Calabi-Yau threefold; we consider this last approach for the Laufer
curve case.Comment: PhD Thesis, 60 pages, 2 PostScript figures. Some sections reshuffled
and some comments added with respect to the version presented at SISSA on
November 28, 2006, according to the suggestions of the examination committee.
A citation removed because of font incompatibilit
Comment on "Nucleon elastic form factors and local duality"
We comment on the papers "Nucleon elastic form factors and local duality"
[Phys. Rev. {\bf D62}, 073008 (2000)] and "Experimental verification of
quark-hadron duality" [Phys. Rev. Lett. {\bf 85}, 1186 (2000)]. Our main
comment is that the reconstruction of the proton magnetic form factor, claimed
to be obtained from the inelastic scaling curve thanks to parton-hadron local
duality, is affected by an artifact.Comment: to appear in Phys. Rev.
Tuning of heat and charge transport by Majorana fermions
We investigate theoretically thermal and electrical conductances for the
system consisting of a quantum dot (QD) connected both to a pair of Majorana
fermions residing the edges of a Kitaev wire and two metallic leads. We
demonstrate that both quantities reveal pronounced resonances, whose positions
can be controlled by tuning of an asymmetry of the couplings of the QD and a
pair of MFs. Similar behavior is revealed for the thermopower, Wiedemann-Franz
law and dimensionless thermoelectric figure of merit. The considered geometry
can thus be used as a tuner of heat and charge transport assisted by MFs
- …