9 research outputs found
Nucleon Axial Form Factor from Lattice QCD
Results for the isovector axial form factors of the proton from a lattice QCD
calculation are presented for both point-split and local currents. They are
obtained on a quenched lattice at with Wilson
fermions for a range of quark masses from strange to charm. We determine the
finite lattice renormalization for both the local and point-split currents of
heavy quarks. Results extrapolated to the chiral limit show that the
dependence of the axial form factor agrees reasonably well with experiment. The
axial coupling constant calculated for the local and the point-split
currents is about 6\% and 12\% smaller than the experimental value
respectively.Comment: 8 pages, 5 figures (included in part 2), UK/93-0
Four-fermion heavy quark operators and light current amplitudes in heavy flavor hadrons
We introduce and study the properties of the "color-straight" four-quark
operators containing heavy and light quark fields. They are of the form (\bar
b\Gamma_b b)(\bar q\Gamma_q q) where both brackets are color singlets. Their
expectation values include the bulk of the nonfactorizable contributions to the
nonleptonic decay widths of heavy hadrons. The expectation values of the
color-straight operators in the heavy hadrons are related to the momentum
integrals of the elastic light-quark formfactors of the respective heavy
hadron. We calculate the asymptotic behavior of the light-current formfactors
of heavy hadrons and show that the actual decrease is 1/(q^2)^3/2 rather than
1/q^4. The two-loop hybrid anomalous dimensions of the four-quark operators and
their mixing (absent in the first loop) are obtained. Using plausible models
for the elastic formfactors, we estimate the expectation values of the
color-straight operators in the heavy mesons and baryons. Improved estimates
will be possible in the future with new data on the radiative decays of heavy
hadrons. We give the Wilson coefficients of the four-fermion operators in the
1/m_b expansion of the inclusive widths and discuss the numerical predictions.
Estimates of the nonfactorizable expectation values are given.Comment: 51 pages. The case of flavor-singlet operators is added for the
two-loop anomalous dimension
Green functions for generalized point interactions in 1D: A scattering approach
Recently, general point interactions in one dimension has been used to model
a large number of different phenomena in quantum mechanics. Such potentials,
however, requires some sort of regularization to lead to meaningful results.
The usual ways to do so rely on technicalities which may hide important
physical aspects of the problem. In this work we present a new method to
calculate the exact Green functions for general point interactions in 1D. Our
approach differs from previous ones because it is based only on physical
quantities, namely, the scattering coefficients, and , to construct .
Renormalization or particular mathematical prescriptions are not invoked. The
simple formulation of the method makes it easy to extend to more general
contexts, such as for lattices of general point interactions; on a line; on
a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR
The Weak Charge of the Proton and New Physics
We address the physics implications of a precision determination of the weak
charge of the proton, QWP, from a parity violating elastic electron proton
scattering experiment to be performed at the Jefferson Laboratory. We present
the Standard Model (SM) expression for QWP including one-loop radiative
corrections, and discuss in detail the theoretical uncertainties and missing
higher order QCD corrections. Owing to a fortuitous cancellation, the value of
QWP is suppressed in the SM, making it a unique place to look for physics
beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and
leptoquarks. We argue that a QWP measurement will provide an important
complement to both high energy collider experiments and other low energy
electroweak measurements. The anticipated experimental precision requires the
knowledge of the order alpha_s corrections to the pure electroweak box
contributions. We compute these contributions for QWP, as well as for the weak
charges of heavy elements as determined from atomic parity violation.Comment: 22 pages of LaTeX, 5 figure
NSM analysis of time-dependent nonlinear buoyancy-driven double-diffusive radiative convection flow in non-Darcy geological porous media
A network numerical simulator is developed and described to simulate the transient, nonlinear buoyancy-driven double diffusive heat and mass transfer of a viscous, incompressible, gray, absorbing–emitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian geological porous regime. The governing boundary-layer equations are formulated in an (X *, Y *, t *) coordinate system with appropriate boundary conditions. An algebraic diffusion approximation is used to simplify the radiation heat transfer contribution. The non-dimensionalized transport equations are solved in an (X, Y, t) coordinate system using the network simulation model (NSM) and the computer code, Pspice. A detailed discussion of the network design is provided. The effects of Prandtl number, radiation–conduction parameter (Stark number), thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the transient dimensionless velocities (U, V), non-dimensional temperature (T) and dimensionless concentration function (C) are illustrated graphically. Additionally, we have computed plots of U, V, T, C versus time and average Nusselt number and Sherwood number versus X, Y coordinate, for various thermophysical parameters. The model finds applications in geological contamination, geothermal energy systems and radioactive waste-repository near-field thermo-geofluid mechanics
ON THE RADIATIVE-CORRECTIONS TO THE ELECTROWEAK PARAMETERS AND PRECISION TESTS OF THE ELECTROWEAK THEORY
GOUNARIS G, Schildknecht D. ON THE RADIATIVE-CORRECTIONS TO THE ELECTROWEAK PARAMETERS AND PRECISION TESTS OF THE ELECTROWEAK THEORY. ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS. 1989;42(1):107-123