63,024 research outputs found
Chiral Corrections to Hyperon Axial Form Factors
We study the complete set of flavor changing hyperon axial current matrix
elements at small momentum transfer. Using partially quenched heavy baryon
chiral perturbation theory, we derive the chiral and momentum behavior of the
axial and induced pseudoscalar form factors. The meson pole contributions to
the latter posses a striking signal for chiral physics. We argue that the study
of hyperon axial matrix elements enables a systematic lattice investigation of
the efficacy of three flavor chiral expansions in the baryon sector. This can
be achieved by considering chiral corrections to SU(3) symmetry predictions,
and their partially quenched generalizations. In particular, despite the
presence of eight unknown low-energy constants, we are able to make
next-to-leading order symmetry breaking predictions for two linear combinations
of axial charges.Comment: 23 pages, 3 figures, typos corrected and a new NLO prediction adde
Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3
The dielectric constant of the incipient ferroelectric EuTiO exhibits a
sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering
of the Eu spins simultaneously appears, indicating coupling between the
magnetism and dielectric properties. This may be attributed to the modification
of the soft-phonon mode, , which is the main contribution to the
large dielectric constant, by the Eu spins(7 per Eu). By adding the
coupling term between the magnetic and electrical subsystems as we show that the variation of the frequency of
soft-phonon mode depends on the spin correlation between the nearest neighbors
Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure
Relativistic Ring-Diagram Nuclear Matter Calculations
A relativistic extension of the particle-particle hole-hole ring-diagram
many-body formalism is developed by using the Dirac equation for
single-particle motion in the medium. Applying this new formalism, calculations
are performed for nuclear matter. The results show that the saturation density
is improved and the equation of state becomes softer as compared to
corresponding Dirac-Brueckner-Hartree-Fock calculations. Using the Bonn A
potential, nuclear matter is predicted to saturate at an energy per nucleon of
--15.30 MeV and a density equivalent to a Fermi momentum of 1.38 fm, in
excellent agreement with empirical information. The compression modulus is 152
MeV at the saturation point.Comment: 23 pages text (LaTex) and 2 figures (paper, will be faxed upon
request), UI-NTH-92-0
Biharmonic Riemannian submersions from 3-manifolds
An important theorem about biharmonic submanifolds proved independently by
Chen-Ishikawa [CI] and Jiang [Ji] states that an isometric immersion of a
surface into 3-dimensional Euclidean space is biharmonic if and only if it is
harmonic (i.e, minimal). In a later paper [CMO2], Cadeo-Monttaldo-Oniciuc shown
that the theorem remains true if the target Euclidean space is replaced by a
3-dimensional hyperbolic space form. In this paper, we prove the dual results
for Riemannian submersions, i.e., a Riemannian submersion from a 3-dimensional
space form of non-positive curvature into a surface is biharmonic if and only
if it is harmonic
Extrapolations of Lattice Meson Form Factors
We use chiral perturbation theory to study the extrapolations necessary to
make physical predictions from lattice QCD data for the electromagnetic form
factors of pseudoscalar mesons. We focus on the quark mass, momentum, lattice
spacing, and volume dependence and apply our results to simulations employing
mixed actions of Ginsparg-Wilson valence quarks and staggered sea quarks. To
determine charge radii at quark masses on the lattices currently used, we find
that all extrapolations except the one to infinite volume make significant
contributions to the systematic error.Comment: 14pp, discussion and Ref. added for disconnected diagram
Crack nucleation using combined crystal plasticity modelling, high-resolution digital image correlation and high-resolution electron backscatter diffraction in a superalloy containing non-metallic inclusions under fatigue
A crystal plasticity finite-element model, which explicitly and directly represents the complex microstructures of a non-metallic agglomerate inclusion within polycrystal nickel alloy, has been developed to study the mechanistic basis of fatigue crack nucleation. The methodology is to use the crystal plasticity model in conjunction with direct measurement at the microscale using high (angular) resolution-electron backscatter diffraction (HR-EBSD) and high (spatial) resolution-digital image correlation (HR-DIC) strain measurement techniques. Experimentally, this sample has been subjected to heat treatment leading to the establishment of residual (elastic) strains local to the agglomerate and subsequently loaded under conditions of low cyclic fatigue. The full thermal and mechanical loading history was reproduced within the model. HR-EBSD and HR-DIC elastic and total strain measurements demonstrate qualitative and quantitative agreement with crystal plasticity results. Crack nucleation by interfacial decohesion at the nickel matrix/agglomerate inclusion boundaries is observed experimentally, and systematic modelling studies enable the mechanistic basis of the nucleation to be established. A number of fatigue crack nucleation indicators are also assessed against the experimental results. Decohesion was found to be driven by interface tensile normal stress alone, and the interfacial strength was determined to be in the range of 1270–1480 MPa
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