Brane superpotential and local Calabi-Yau manifolds

We briefly report on some recent progress in the computation of B-brane superpotentials for Type II strings compactified on Calabi-Yau manifolds, obtained by using a parametrization of tubular neighborhoods of complex submanifolds, also known as local spaces. In particular, we propose a closed expression for the superpotential of a brane on a genus-g curve in a Calabi-Yau threefold in the case in which there exists a holomorphic projection from the local space around the curve to the curve itself.Comment: 3 pages, contribution to the proceedings of the workshop "Progress of String Theory and Quantum Field Theory", Osaka City University, December 200

Backgrounds in Boundary String Field Theory

We study the role of closed string backgrounds in boundary string field theory. Background independence requires the introduction of dual boundary fields, which are reminiscent of the doubled field formalism. We find a correspondence between closed string backgrounds and collective excitations of open strings described by vertex operators involving dual fields. Renormalization group flow, solutions and stability are discussed in an example.Comment: Contribution to proceedings of SFT09 in 'Theoretical and Mathematical Physics', Russian Academy of Science

On the Correspondence of Open and Closed Strings

This thesis investigates correspondences between open and closed strings. This is done on the level of coupled open-closed moduli spaces and from a string field theoretic point of view. The construction of boundary string field theory on Wess-Zumino-Witten models leads to a conjecture on closed string backgrounds appearing as non-local operators in open string field theory. Sample computations for tachyon condensation leading to curved branes support this conjecture. Additional steps are taken to study supersymmetric string theories on Calabi-Yau manifolds in the presence of bulk and boundary moduli. For the topological B-model effective bulk-induced superpotentials for D5-branes are computed to all orders in the open string couplings.Comment: PhD thesis, 166 page

Tailoring of phononic band structures in colloidal crystals

We report an experimental study of the elastic properties of a two-dimensional (2D) colloidal crystal subjected to light-induced substrate potentials. In agreement with recent theoretical predictions [H.H. von Gruenberg and J. Baumgartl, Phys. Rev. E 75, 051406 (2007)] the phonon band structure of such systems can be tuned depending on the symmetry and depth of the substrate potential. Calculations with binary crystals suggest that phononic band engineering can be also performed by variations of the pair potential and thus opens novel perspectives for the fabrication of phononic crystals with band gaps tunable by external fields.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Open-closed string correspondence: D-brane decay in curved space

This paper analyzes the effect of curved closed string backgrounds on the stability of D-branes within boundary string field theory. We identify the non-local open string background that implements shifts in the closed string background and analyze the tachyonic sector off-shell. The renormalization group flow reveals some characteristic properties, which are expected for a curved background, like the absence of a stable space-filling brane. In 3-dimensions we describe tachyon condensation processes to lower-dimensional branes, including a curved 2-dimensional brane. We argue that this 2-brane is perturbatively stable. This is in agreement with the known maximally symmetric WZW-branes and provides further support to the bulk-boundary factorization approach to open-closed string correspondence.Comment: 23 pages, harvma

Visualization of the birth of an optical vortex using diffraction from a triangular aperture

Funding: EPSRC, UKThe study and application of optical vortices have gained significant prominence over the last two decades. An interesting challenge remains the determination of the azimuthal index (topological charge) l of an optical vortex beam for a range of applications. We explore the diffraction of such beams from a triangular aperture and observe that the form of the resultant diffraction pattern is dependent upon both the magnitude and sign of the azimuthal index and this is valid for both monochromatic and broadband light fields. For the first time we demonstrate that this behavior is related not only to the azimuthal index but crucially the Gouy phase component of the incident beam. In particular, we explore the far field diffraction pattern for incident fields incident upon a triangular aperture possessing non-integer values of the azimuthal index l. Such fields have a complex vortex structure. We are able to infer the birth of a vortex which occurs at half-integer values of l and explore its evolution by observations of the diffraction pattern. These results demonstrate the extended versatility of a triangular aperture for the study of optical vortices. (c) 2011 Optical Society of AmericaPublisher PDFPeer reviewe

Development of a highly precise place recognition module for effective human-robot interactions in changing lighting and viewpoint conditions

We present a highly precise and robust module for indoor place recognition, extending the work by Lemaignan et al. and Robert Jr. by giving the robot the ability to recognize its environment context. We developed a full end-to-end convolutional neural network architecture, using a pre-trained deep convolutional neural network and the explicit inductive bias transfer learning strategy. Experimental results based on the York University and Rzeszów University dataset show excellent performance values (over 94.75 and 97.95 percent accuracy) and a high level of robustness over changes in camera viewpoint and lighting conditions, outperforming current benchmarks. Furthermore, our architecture is 82.46 percent smaller than the current benchmark, making our module suitable for embedding into mobile robots and easily adoptable to other datasets without the need for heavy adjustments