26,779 research outputs found
Induced pseudoscalar form factor of the nucleon at two-loop order in chiral perturbation theory
We calculate the imaginary part of the induced pseudoscalar form factor of
the nucleon in the framework of two-loop heavy baryon chiral
perturbation theory. The effect of the calculated three-pion continuum on the
pseudoscalar constant measurable in
ordinary muon capture turns out to be negligibly small.
Possible contributions from counterterms at two-loop order are numerically
smaller than the uncertainty of the dominant pion-pole term proportional to the
pion-nucleon coupling constant . We conclude that a
sufficiently accurate representation of the induced pseudoscalar form factor of
the nucleon at low momentum transfers is given by the sum of the pion-pole
term and the Adler-Dothan-Wolfenstein term: , with fm
the axial mean square radius of the nucleon.Comment: 6 pages, 2 figures, accepted for publication in Physical Review
On the analysis of the pion--nucleon --term: The size of the remainder at the Cheng--Dashen point
We calculate the one--loop contributions of order to the difference
between the on--shell pion--nucleon scattering amplitude
at the Cheng--Dashen point , and
the scalar form factor in the framework of heavy baryon
chiral perturbation theory. We proof that to this order contains
chiral logarithms and therefore it vanishes simply as in the
chiral limit. Numerically, we find as an upper limit MeV.Comment: 7 pp, LaTeX, uses epsf, 1 figure in separate PS fil
Poisson algebra of 2d dimensionally reduced gravity
Using a Lax pair based on twisted affine Kac-Moody and Virasoro
algebras, we deduce a r-matrix formulation of two dimensional reduced vacuum
Einstein's equations. Whereas the fundamental Poisson brackets are
non-ultralocal, they lead to pure c-number modified Yang-Baxter equations. We
also describe how to obtain classical observables by imposing reasonable
boundaries conditions.Comment: 16 pages, minor corrections. To appear in JHE
Double neutral pion photoproduction at threshold
We consider the chiral expansion of the threshold amplitude for the reaction
to order . We substantiate a
claim that this photoproduction channel is significantly enhanced close to
threshold due to pion loops. A precise measurement of the corresponding cross
sections is called for which allows to test chiral perturbation theory.Comment: 8 pp, LaTe
Partially Quenched QCD with Non-Degenerate Dynamical Quarks
We discuss the importance of using partially quenched theories with three
degenerate quarks for extrapolating to QCD, and present some relevant results
from chiral perturbation theory.Comment: LATTICE99 talk. 3 pages, 2 figures. Uses epsf and espcrc2.st
Threshold Two-Pion Photo- and Electroproduction: More neutrals than expected
We present an exploratory study of two pion photo-- and electroproduction off
the nucleon in the threshold region. To calculate the pertinent amplitudes, we
make use of heavy baryon chiral perturbation theory. We show that due to finite
chiral loops the production cross section for final states with two neutral
pions is considerably enhanced. The experimental implications are briefly
discussed.Comment: 23pp, plain TeX, 11 figures available upon request, CRN 94/1
Low--Energy Theorems for Weak Pion Production
We derive novel low--energy theorems for single pion production off nucleons
through the isovector axial current. We find that the -dependence of the
multipole at threshold is given by the nucleon scalar form
factor, namely . The relation to
PCAC results for soft pions including electroweak form factors is also
clarified.Comment: 9 pp, TeX, 2 figures available as ps files, CRN 93-5
The Reaction at Threshold
We consider the chiral expansion for the reaction in
heavy baryon chiral perturbation theory. To order we derive novel
low--energy theorems that compare favorably with recent determinations of the
total cross sections for and .Comment: 7 pp, LateX (uses epsf.sty), 3 figures appended as ps files (split
off as ppnf1.ps,ppnf2.ps,ppnf3.ps), CRN 94/1
New Developments in Gaming Taxation and Regulation: an Update
The gaming industry is facing increased regulatory interest. Congress has authorized a commission to investigate gaming in the United States. The Internal Revenue Service continues to interpret ambiguous areas of the tax code in an attempt to raise gaming tax revenues. Regulatory changes in currency transaction reporting have also resulted in some significant changes for the industry. The purpose of this paper is to provide an update on tax and regulatory issues currently facing the gaming industry. Specifically, the paper will address tax and regulatory developments in: (a) tip compliance, (b) cash transaction reporting, (c) complimentaries, (d) employee cafeterias, (e) outstanding chips and tokens, (e) marker discounts, and (f) high-denomination slot win reporting
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