A non-perturbative study of non-commutative U(1) gauge theory

We study U(1) gauge theory on a 4d non-commutative torus, where two directions are non-commutative. Monte Carlo simulations are performed after mapping the regularized theory onto a U(N) lattice gauge theory in d=2. At intermediate coupling strength, we find a phase in which open Wilson lines acquire non-zero vacuum expectation values, which implies the spontaneous breakdown of translational invariance. In this phase, various physical quantities obey clear scaling behaviors in the continuum limit with a fixed non-commutativity parameter theta, which provides evidence for a possible continuum theory. In the weak coupling symmetric phase, the dispersion relation involves a negative IR-singular term, which is responsible for the observed phase transition.Comment: 7 pages, 4 figures, Talk presented by J. Nishimura at the 21st Nishinomiya-Yukawa Memorial Symposium on Theoretical Physics: ``Noncommutative Geometry and Quantum Spacetime in Physics'', Nishinomiya and Kyoto (2006

Optical and SAR data integration for automatic change pattern detection

ISPRS Technical Commission VII Symposium, 29 September – 2 October 2014, Istanbul, TurkeyAutomatic change pattern mapping in urban and sub-urban area is important but challenging due to the diversity of urban land use pattern. With multi-sensor imagery, it is possible to generate multidimensional unique information of Earth surface features that allow developing a relationship between a response of each feature to synthetic aperture radar (SAR) and optical sensors to track the change automatically. Thus, a SAR and optical data integration framework for change detection and a relationship for automatic change pattern detection were developed. It was carried out in three steps: (i) Computation of indicators from SAR and optical images, namely: normalized difference ratio (NDR) from multi-temporal SAR images and the normalized difference vegetation index difference ( NDVI) from multi-temporal optical images, (ii) computing the change magnitude image from NDR and ΔNDVI and delineating the change area and (iii) the development of an empirical relationship, for automatic change pattern detection. The experiment was carried out in an outskirts part of Ho Chi Minh City, one of the fastest growing cities in the world. The empirical relationship between the response of surface feature to optical and SAR imagery has successfully delineated six changed classes in a very complex urban sprawl area that was otherwise impossible with multi-spectral imagery. The improvement of the change detection results by making use of the unique information on both sensors, optical and SAR, is also noticeable with a visual inspection and the kappa index was increased by 0.13 (0.75 to 0.88) in comparison to only optical images

Simulation Results for U(1) Gauge Theory on Non-Commutative Spaces

We present numerical results for U(1) gauge theory in 2d and 4d spaces involving a non-commutative plane. Simulations are feasible thanks to a mapping of the non-commutative plane onto a twisted matrix model. In d=2 it was a long-standing issue if Wilson loops are (partially) invariant under area-preserving diffeomorphisms. We show that non-perturbatively this invariance breaks, including the subgroup SL(2,R). In both cases, d=2 and d=4, we extrapolate our results to the continuum and infinite volume by means of a Double Scaling Limit. In d=4 this limit leads to a phase with broken translation symmetry, which is not affected by the perturbatively known IR instability. Therefore the photon may survive in a non-commutative world

Open Semiclassical Strings and Long Defect Operators in AdS/dCFT Correspondence

We consider defect composite operators in a defect superconformal field theory obtained by inserting an AdS_4 x S^2-brane in the AdS_5 x S^5 background. The one-loop dilatation operator for the scalar sector is represented by an integrable open spin chain. We give a description to construct coherent states for the open spin chain. Then, by evaluating the expectation value of the Hamiltonian with the coherent states in a long operator limit, a Landau-Lifshitz type of sigma model action is obtained. This action is also derived from the string action and hence we find a complete agreement in both SYM and string sides. We see that an SO(3)_H pulsating string solution is included in the action and its energy completely agrees with the result calculated in a different method. In addition, we argue that our procedure would be applicable to other AdS-brane cases.Comment: 22 pages, 1 figure, LaTeX, minor corrections and references added. v3) some new results added. shortened and accepted version in PR

First Simulation Results for the Photon in a Non-Commutative Space

We present preliminary simulation results for QED in a non-commutative 4d space-time, which is discretized to a fuzzy lattice. Its numerical treatment becomes feasible after its mapping onto a dimensionally reduced twisted Eguchi-Kawai matrix model. In this formulation we investigate the Wilson loops and in particular the Creutz ratios. This is an ongoing project which aims at non-perturbative predictions for the photon, which can be confronted with phenomenology in order to verify the possible existence of non-commutativity in nature.Comment: 3 pages, 4 figures, talk presented by J. Volkholz at Lattice2004(theory

Depletion of density of states near Fermi energy induced by disorder and electron correlation in alloys

We have performed high resolution photoemission study of substitutionally disordered alloys Cu-Pt, Cu-Pd, Cu-Ni, and Pd-Pt. The ratios between alloy spectra and pure metal spectra are found to have dips at the Fermi level when the residual resistivity is high and when rather strong repulsive electron-electron interaction is expected. This is in accordance with Altshuler and Aronov's model which predicts depletion of density of states at the Fermi level when both disorder and electron correlation are present.Comment: 1 tex file and 4 ps file

INTEGRATING MULTI-TEMPORAL SAR IMAGES AND GPS DATA TO MONITOR THREE-DIMENSIONAL LAND SUBSIDENCE

Synthetic aperture radar (SAR) is an effective means of monitoring land subsidence, and differential interferometric SAR (DInSAR) is commonly used to acquire the necessary data. In particular, persistent scatterer interferometry (PSI) can be used to measure land subsidence accurately over a wide area from multi-temporal SAR images. However, the estimated displacement is obtained only in the radar line-of-sight (LOS) direction, making it necessary to develop a method for measuring three-dimensional displacements by combining multidirectional observations. Therefore, we propose herein a method for estimating three-dimensional displacement velocities by combining the results from PSI and geodetic deformation measurements, namely, Global Positioning System and leveling data. We apply the least-squares method to Kansai International Airport in Japan by using 13 ALOS-2/PALSAR-2 ascending images from 2014 to 2018 and 17 ALOS-2/PALSAR-2 descending images from 2015 to 2018. In validation, the rootmean- square errors are 14, 16, and 14 mm/year for the east–west, north–south, and vertical components, respectively, showing that combining PSI results and geodetic deformation measurements is effective for monitoring land subsidence

Optical conductivity of the Kondo insulator YbB_12: Gap formation and low-energy excitations

Optical reflectivity experiments have been conducted on single crystals of the Kondo insulator YbB_12 in order to obtain its optical conductivity, \sigma(\omega). Upon cooling below 70 K, a strong supression of \sigma(\omega) is seen in the far-infrared region, indicating the opening of an energy gap of ~ 25 meV. This gap development is coincident with a rapid decrease in the magnetic susceptibility, which shows that the gap opening has significant influence on magnetic properties. A narrow, asymmetric peak is observed at ~40 meV in \sigma(\omega), which is attributed to optical transitions between the Yb 4f-derived states across the gap. In addition, a broad peak is observed at ~0.25 eV. This peak is attributed to transitions between Yb 4f-derived states and p-d band, and is reminiscent of similar peaks previously observed for rare-earth hexaborides.Comment: 4 pages, 4 figure

Two-Dimensional Confinement of 3d1 Electrons in LaTiO3/LaAlO3 Multilayers

We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO3)n(LaAlO3)5 multilayers with n = 1-3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d^1 state of the Ti ions. In combination with LDA+U calculations, we suggest that 2D confinement in the TiO2 slabs lifts the degeneracy of the t_{2g} states leaving only the planar d_xy orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t_{2g} 2D Hubbard model.Comment: 7 pages, 4 figures. Accepted for publication in Phys. Rev. Let