2,169 research outputs found
Lattice baryons in the 1/N expansion
Results are presented for hadron spectroscopy with gauge groups SU(N) with
N=3, 5, 7. Calculations use the quenched approximation. Lattice spacings are
matched using the static potential. Meson spectra show independence on N and
vacuum-to-hadron matrix elements scale as the square root of N. The baryon
spectrum shows the excitation levels of a rigid rotor.Comment: 19 pages, 11 figure
Implementation of a Two-Dimensional Hydrodynamic Shock Code Based Upon the Weighted Average Flux Method
Numerical modeling of shock propagation and reflection is of interest to the Department of Defense (DoD). Propriety state-of-the-art codes based upon E. F. Toro\u27s weighted average flux (WAF) method are being used to investigate complex shock reflection phenomena. Here we develop, test, and validate a one-dimensional hydrodynamic shock code. We apply WAF to Gudonov\u27s first-order upwind method to achieve second-order accuracy. Oscillations, typical of second-order methods, are then removed using adaptive weight limiter functions based upon total variation diminishing (TVD) flux limiters. An adaptive Riemann solver routine is also implemented to improve computational efficiency. This one-dimensional code is then extended into two dimensions via Warming and Beam\u27s variation on dimensional splitting. The numerical capabilities of the two-dimensional code are demonstrated by modeling the detonation of a cylindrically symmetric explosive with the axis of the cylinder oriented horizontally above an ideal surface
Weak low-energy couplings from topological zero-mode wavefunctions
We discuss a new method to determine the low-energy couplings of the weak Hamiltonian in the -regime. It relies on a matching of the
topological poles in of three-point functions of two pseudoscalar
densities and a four-fermion operator computed in lattice QCD, to the same
observables in the Chiral Effective Theory. We present the results of a NLO
computation in chiral perturbation theory of these correlation functions
together with some preliminary numerical results.Comment: 7 pages. Contribution to Lattice 200
Determination of the weak Hamiltonian in the SU(4) chiral limit through topological zero-mode wave functions
A new method to determine the low-energy couplings of the weak
Hamiltonian is presented. It relies on a matching of the topological poles in
of three-point correlators of two pseudoscalar densities and a
four-fermion operator, measured in lattice QCD, to the same observables
computed in the -regime of chiral perturbation theory. We test this
method in a theory with a light charm quark, i.e. with an SU(4) flavour
symmetry. Quenched numerical measurements are performed in a 2 fm box, and
chiral perturbation theory predictions are worked out up to next-to-leading
order. The matching of the two sides allows to determine the weak low-energy
couplings in the SU(4) limit. We compare the results with a previous
determination, based on three-point correlators containing two left-handed
currents, and discuss the merits and drawbacks of the two procedures.Comment: 38 pages, 9 figure
Nanoscale austenite reversion through partitioning, segregation, and kinetic freezing: Example of a ductile 2 GPa Fe-Cr-C steel
Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite
results in an ultrahigh strength ferritic stainless steel with excellent
ductility. The austenite reversion mechanism is coupled to the kinetic freezing
of carbon during low-temperature partitioning at the interfaces between
martensite and retained austenite and to carbon segregation at
martensite-martensite grain boundaries. An advantage of austenite reversion is
its scalability, i.e., changing tempering time and temperature tailors the
desired strength-ductility profiles (e.g. tempering at 400{\deg}C for 1 min.
produces a 2 GPa ultimate tensile strength (UTS) and 14% elongation while 30
min. at 400{\deg}C results in a UTS of ~ 1.75 GPa with an elongation of 23%).
The austenite reversion process, carbide precipitation, and carbon segregation
have been characterized by XRD, EBSD, TEM, and atom probe tomography (APT) in
order to develop the structure-property relationships that control the
material's strength and ductility.Comment: in press Acta Materialia 201
Leptonic and Semileptonic Decays of Pseudoscalar Mesons
We employ the relativistic constituent quark model to give a unified
description of the leptonic and semileptonic decays of pseudoscalar mesons
(\pi, K, D, D_s, B, B_s). The calculated leptonic decay constants and form
factors are found to be in good agreement with available experimental data and
other approaches. We reproduce the results of spin-flavor symmetry in the heavy
quark limit.Comment: 12 pages LaTeX (elsart.sty) + 4 figures; added references, to appear
in Phys. Lett.
Non-perturbative quark mass renormalization
We show that the renormalization factor relating the renormalization group
invariant quark masses to the bare quark masses computed in lattice QCD can be
determined non-perturbatively. The calculation is based on an extension of a
finite-size technique previously employed to compute the running coupling in
quenched QCD. As a by-product we obtain the --parameter in this theory
with completely controlled errors.Comment: Talk given at LATTICE '97, 6 pages, Latex source, 7 eps figures,
needs epsfi
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