2,094 research outputs found
The cutoff-dependence of the Casimir force within an inhomogeneous medium
We consider the ground state energy of the electromagnetic field in a piston
geometry. In the idealised case, where the piston and the walls of the chamber
are taken as perfect mirrors, the Casimir pressure on the piston is finite and
independent of the small scale physics of the media that compose the mirrors;
the Casimir-energy of the system can be regularised and is cutoff-independent.
Yet we find that, when the body of the piston is filled with an inhomogeneous
dielectric medium, the Casimir energy is cutoff-dependent, and the value of the
pressure is thus inextricably dependent on the detailed behaviour of the mirror
and the medium at large wave-vectors. This result is inconsistent with recent
proposals for regularising Casimir forces in inhomogeneous media.Comment: 6 pages, 2 figure
The pi-N Sigma term - a lattice investigation
A lattice calculation of the pi-N sigma term is described using dynamical
staggered fermions. Preliminary results give a sea term comparable in magnitude
to the valence term.Comment: Latex article. 6 pages, uuencoded compressed tar file. Contribution
to the Kyffhaeuser Workshop (Leipzig, Germany, September 1993). HLRZ preprint
93-6
The ``Spin'' Structure of the Nucleon - a lattice investigation
We will discuss here an indirect lattice evaluation of the baryon axial
singlet current matrix element. This quantity may be related to the fraction of
nucleon spin carried by the quarks. The appropriate structure function has
recently been measured (EMC experiment). As in this experiment, we find that
the quarks do not appear to carry a large component of the nucleon spin.Comment: Latex article. 3 pages. Contribution to the Second IMACS Conference
on Computational Physics, Cahokia, U.S.A. October 1993. HLRZ preprint 93-7
Hadronic coupling constants in lattice QCD
We report on calculations of the hadronic coupling constants
and based on lattice QCD with four flavors of dynamical staggered
fermions. By computing 2--point and 3--point Green's functions we have been
able to determine these coupling constants ab initio from QCD; the results are
compatible with the experimental values.Comment: 3 Page
Effective Yukawa Couplings in Noncompact Lattice QED
We investigate effective Yukawa couplings of mesons to the elementary
fermions in noncompact lattice QED. The couplings are extracted from suitable
fermion-antifermion-meson three-point functions calculated by Monte Carlo
simulations with dynamical staggered fermions. The scaling behaviour is
compatible with expectations from perturbation theory, thus indicating
triviality of QED. The lines of constant Yukawa coupling are compared to flows
of other quantities. Consistency is seen, at most, for weak coupling.Comment: 12 pages, uuencoded compressed postscrip
Is the Chiral Phase Transition in Non-Compact Lattice QED Driven by Monopole Condensation?
We investigate the recent conjecture that the chiral phase transition in
non-compact lattice QED is driven by monopole condensation. The comparison of
analytic and numerical results shows that we have a quantitative understanding
of monopoles in both the quenched and dynamical cases. We can rule out monopole
condensation.Comment: 21 pages, 10 postscript figures include
Hadronic Coupling Constants in Lattice QCD
We calculate the hadronic coupling constants and
in QCD, including dynamical quarks in the framework of staggered fermions in
the lattice approach. For the nucleon--pion coupling we obtain , to be compared with the experimental value . The
coupling has been analysed for two different sets of operators
with the averaged result which is to be compared
with the experimental value .Comment: 14 pages uuencoded postscript fil
- …