The Hydrodynamical Limit of Quantum Hall system

We study the current algebra of FQHE systems in the hydrodynamical limit of small amplitude, long-wavelength fluctuations. We show that the algebra simplifies considerably in this limit. The hamiltonian is expressed in a current-current form and the operators creating inter-Landau level and lowest Landau level collective excitations are identified.Comment: Revtex, 16 page

Analysis of melt-textured YBCO with nanoscale inclusions

Recently, particles with the chemical composition Y2Ba 4CuMOx where M U, Nb, Zr, etc., and sizes in the range of 50 - 200 nm have been generated within the YBCO matrix of bulk, melt-processed superconductors in order to serve as effective flux pinning sites. By means of AFM and electron backscatter diffraction (EBSD) measurements, we analyse the spatial distribution and the size distribution of these nanoparticles within the superconducting YBCO matrix

Natural Gauge Hierarchy in SO(10)

It is shown that a natural gauge hierarchy and doublet-triplet splitting can be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial cancellations (fine-tuning) and arbitrary forms of the superpotential are avoided, the superpotential being the most general compatible with a symmetry. It is shown by example that the Dimopoulos-Wilczek mechanism can be protected against the effects of higher-dimension operators possibly induced by Planck-scale physics. Natural implementation of the mechanism leads to an automatic Peccei-Quinn symmetry. The same local symmetries that would protect the gauge hierarchy against Planck-scale effects tend to protect the axion also. It is shown how realistic quark and lepton masses might arise in this framework. It is also argued that ``weak suppression'' of proton decay can be implemented more economically than can ``strong suppression'', offering some grounds to hope (in the context of SO(10)) that proton decay could be seen at Superkamiokande.Comment: 26 pages in plain LaTeX, 5 figures available on request, BA-94-0

Recent direct measurement of the Top quark mass and quasi-infrared fixed point

We note that the recent direct measurement of the top quark mass at $173.3 \pm 5.6 (stat) \pm 6.2 (syst)$ by D0 collaboration severely constrains the theoretically attractive infra-red fixed point scenario of the top quark Yukawa coupling in supersymmetric GUTs. For one-step unified models the above mentioned measurement bounds the arbitrary but experimentally determinable parameter $\tan \beta$ to the range $1.3 \le \tan \beta \le 2.1$. Further crunch on the top quark mass may determine $\tan \beta$ even more accurately within the fixed point scenario. On the other hand an experimental value of $\tan \beta > 2.1$ will rule out the fixed point scenario bounding $h^2_t(M_X)/4 \pi$ to 0.022 from above.Comment: 7 pages, Latex with epsf style, 1 figure, captions.st

Micromagnetic Simulation of Spin Transfer Torque Switching of Full-Heusler Co2FeAl0.5Si0.5 Alloy Thin Elliptical Disc

AbstractWe report micromagnetic simulation of spin transfer torque (STT) switching of a thin elliptical disc made of full-Heusler Co2FeAl0.5Si0.5 alloy. The STT results in switching the direction of initial magnetization of the disc to a new state based on the spin-polarization factor (ƞ) of the material and magnitude of current density (J) applied. The value of J required for magnetization switching need to be reduced in the order of 106 A/cm2. In our simulation we obtained 3 × 105 A/cm2 as the critical current density (Jc) required for complete magnetization switching of the disc. We analyzed the effect of ƞ on magnetization switching time by reducing the value of ƞ by 0.10 from the actual value of 0.76. The decrement in ƞ results in the increment of time taken to switch the direction of magnetization. The change in switching time for variable disc thickness was also studied. This simulation result holds a key factor in the study of STT switching in spin-valve nanopillar

New vector-scalar contributions to neutrinoless double beta decay and constraints on R-parity violation

We show that in minimal supersymmetric standard model (MSSM) with R-parity breaking as well as in the left-right symmetric model, there are new observable contributions to neutrinoless double beta decay arising from hitherto overlooked diagrams involving the exchange of one W boson and one scalar boson. In particular, in the case of MSSM, the present experimental bounds on neutrinoless double beta decay lifetime improves the limits on certain R-parity violating couplings by about two orders of magnitude. It is shown that similar diagrams also lead to enhanced rates for $\mu^-\rightarrow e^+$ conversion in nuclei, which are in the range accessible to ongoing experiments.Comment: Latex file; 9 pages; 3 figures available on reques

EBSD characterisation of Y2Ba4CuUOx phase in melttextured YBCO with addition of depleted uranium oxide

Melt-textured YBCO samples processed with added Y2O3 and depleted uranium oxide (DU) contain nano-particles, which have been identified previously as Y2Ba4CuUOx (U-411). This phase has a cubic unit cell, which is clearly distinct from the orthorhombic Y-123 and Y-211 phases within the YBCO system. In samples with a high amount of DU addition (0.8 wt-% DU), U-2411 particles have sizes between 200 nm and several νm, so identification of the Kikuchi patterns of this phase becomes possible. Together with a parallel EDX analysis, the particles embedded in the Y-123 matrix can be identified unambiguously. In this way, a three-phase EBSD scan becomes possible, allowing also the identification of nanometre-sized particles in the sample microstructure