5,140 research outputs found
SU(N) Coherent States
We generalize Schwinger boson representation of SU(2) algebra to SU(N) and
define coherent states of SU(N) using bosonic harmonic
oscillator creation and annihilation operators. We give an explicit
construction of all (N-1) Casimirs of SU(N) in terms of these creation and
annihilation operators. The SU(N) coherent states belonging to any irreducible
representations of SU(N) are labelled by the eigenvalues of the Casimir
operators and are characterized by (N-1) complex orthonormal vectors describing
the SU(N) manifold. The coherent states provide a resolution of identity,
satisfy the continuity property, and possess a variety of group theoretic
properties.Comment: 25 pages, LaTex, no figure
Dark Matter from Early Decays
Two leading dark matter candidates from supersymmetry and other theories of
physics beyond the standard model are WIMPs and weak scale gravitinos. If the
lightest stable particle is a gravitino, then a WIMP will decay into it with a
natural lifetime of order a month ~ M_{pl}^2/M_{weak}^3. We show that if the
bulk of dark matter today came from decays of neutral particles with lifetimes
of order a year or smaller, then it could lead to a reduction in the amount of
small scale substructure, less concentrated halos and constant density cores in
the smallest mass halos. Such beneficial effects may therefore be realized
naturally, as discussed by Cembranos, Feng, Rajaraman, and Takayama, in the
case of supersymmetry.Comment: Matches version accepted for publication in PRD. Added a paragraph to
Sec V. 9 pages, 3 figure
Amenorrhea Due to Defects in Steroid Biosynthesis
Amenorrhea as the first manifestation of a steroid biosynthetic defect is rather unusual. The common forms of congenital adrenal hyperplasia are classic examples of steroid biosynthetic defects. Yet in genotypic females, this disorder is usually evident from birth because of virilization. Effective treatment usually ensues and amenorrhea is only a problem when control is inadequate. However, there are individuals whose disorder will be manifest for the first time in the postnatal or adult period. In addition, multiple other steroid defects have now been clearly delineated. Many of these individuals will have amenorrhea, virilization, or sexual ambiguities as part of the clinical picture. The paper will describe some of the more clearly delineated steroidal biosynthetic defects. Also the clinical management of patients with postnatal onset of 21-hydroxylase deficiency form of congenital adrenal hyperplasia will be discussed
A (1,2) Heterotic String with Gauge Symmetry
We construct a (1,2) heterotic string with gauge symmetry and determine its
particle spectrum. This theory has a local N=1 worldsheet supersymmetry for
left movers and a local N=2 worldsheet supersymmetry for right movers and
describes particles in either two or three space-time dimensions. We show that
fermionizing the bosons of the compactified N=1 space leads to a particle
spectrum which has nonabelian gauge symmetry. The fermionic formulation of the
theory corresponds to a dimensional reduction of self dual Yang Mills. We also
give a worldsheet action for the theory and calculate the one-loop path
integral.Comment: 17 pages, added reference
Fractography, elastic modulus and oxidation resistance of novel metal-intermetallic Ni/Ni 3Al multilayer films
Novel metal–intermetallic Ni/Ni3Al multilayer films are synthesized by a magnetron sputtering technique. The fractography, elastic modulus, and the oxidation resistance of the multilayer films are studied by a series of experimental tests. The scanning electron microscopy fractography of the films shows that both Ni and Ni3Al layers fracture with the appearance of ductile metal failure. No metal–intermetallic delamination appears in the multilayered films. Fluted dimpling in each Ni and Ni3Al layer is
evident and continuous, layer through layer, illustrating very good adherence among the constituent layers. Such adherence makes the toughness of the Ni layers capable of transferring into the Ni3Al layers. Young’s modulus of the Ni/Ni3Al film is found to be 226 and 253 ± 10 GPa by nanoindentation and laser acoustic techniques, respectively. The continuity of elastic modulus between the two phases is revealed by nanoindentation test. The modulus continuity indicates an excellent integration of the
constituent layers with similar crystal structure and close lattice constants. This integration makes the multilayers unsurpassed in comprehensive mechanical properties. Sheet resistance measurements show a good protective ability of the Ni/Ni3Al
multilayers during high temperature oxidation. X-ray photoelectron spectroscopy spectra suggest that crystallized Al2O3 /Ni scales formed during the deposition and subsequent annealing processes are apparently responsible for the stability of these
films under oxidative conditions. The appearance of the crystallized Al2O3 /Ni thin scales on the top of Ni3Al layers provides the Ni/Ni3Al multilayers good thermal oxidation resistance without lowering the fracture toughness.published_or_final_versio
Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3
The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.Comment: 26 pages, 9 figure
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