995 research outputs found
Baryon Masses in Chiral Perturbation Theory with Infrared Regularization
The baryon masses are examined in SU(3) chiral perturbation theory to third
order using the recently proposed infrared regularization scheme. Fourth order
is estimated by evaluating the dominant diagram. With this regularization the
magnitude of the loop integrals is reduced so that the convergence of the
series appears to be better than in the heavy baryon approach.Comment: The original third order calculation is supplemented by an estimate
of fourth order using just the dominant diagram. The convergence still
appears to be better than in the heavy baryon approach. To be published in
Phys. Rev. C. 15 pages latex, 2 postscript figure
On the effects of (partial) quenching on penguin contributions to K-> pi pi
Recently, we pointed out that chiral transformation properties of strong
penguin operators change in the transition from unquenched to (partially)
quenched QCD. As a consequence, new penguin-like operators appear in the
(partially) quenched theory, along with new low-energy constants, which should
be interpreted as a quenching artifact. Here, we extend the analysis to the
contribution of the new low-energy constants to the K^0 -> pi^+ pi^- amplitude,
at leading order in chiral perturbation theory, and for arbitrary (momentum
non-conserving) kinematics. Using these results, we provide a detailed
discussion of the intrinsic systematic error due to this (partial) quenching
artifact. We also give a simple recipe for the determination of the
leading-order low-energy constant parameterizing the new operators in the case
of strong penguins.Comment: 17 pages, 1 figure, minor correction
Aspects of Nucleon Compton Scattering
We consider the spin-averaged nucleon forward Compton scattering amplitude in
heavy baryon chiral perturbation theory including all terms to order . The chiral prediction for the spin-averaged forward Compton scattering
amplitude is in good agreement with the data for photon energies MeV. We also evaluate the nucleon electric and magnetic Compton
polarizabilities to this order and discuss the uncertainties of the various
counter terms entering the chiral expansion of these quantities.Comment: 17 pp, TeX, 7 figures available from the authors, preprint CRN-93/5
Scaling tests of the improved Kogut-Susskind quark action
Improved lattice actions for Kogut-Susskind quarks have been shown to improve
rotational symmetry and flavor symmetry. In this work we find improved scaling
behavior of the rho and nucleon masses expressed in units of a length scale
obtained from the static quark potential, and better behavior of the Dirac
operator in instanton backgrounds.Comment: 4 pages, 4 figures, Revte
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