26 research outputs found
Dynamical Polarizabilities of SU(3) Octet of Baryons
We present calculations and an analysis of the spin-independent dipole
electric and magnetic dynamical polarizabilities for the lowest in mass SU(3)
octet of baryons. These extensive calculations are made possible by the recent
implementation of semi-automatized calculations in Chiral Perturbation Theory
which allows evaluating dynamical spin-independent electromagnetic
polarizabilities from Compton scattering up to next-to-the-leading order. Our
results are in good agreement with calculations performed for nucleons found in
the literature. The dependencies for the range of photon energies up to 1 GeV,
covering the majority of the meson photo production channels, are analyzed. The
separate contributions into polarizabilities from the various baryon meson
clouds are studied.Comment: 10 pages, 7 figures, extended analysis of hyperon polarizabilitie
Nucleon polarizabilities in the perturbative chiral quark model
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context
of the perturbative chiral quark model. We demonstrate that meson cloud effects
are sufficient to explain the electric polarizability of nucleon. Contributions
of excite quark states to the paramagnetic polarizability are dominant and
cancel the diamagnetic polarizability arising from the chiral field. The
obtained results are compared to data and other theoretical predictions.Comment: 25 pages, 18 figures, 2 table
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
Virtual Compton Scattering off the Nucleon in Chiral Perturbation Theory
We investigate the spin-independent part of the virtual Compton scattering
(VCS) amplitude off the nucleon within the framework of chiral perturbation
theory. We perform a consistent calculation to third order in external momenta
according to Weinberg's power counting. With this calculation we can determine
the second- and fourth-order structure-dependent coefficients of the general
low-energy expansion of the spin-averaged VCS amplitude based on gauge
invariance, crossing symmetry and the discrete symmetries. We discuss the
kinematical regime to which our calculation can be applied and compare our
expansion with the multipole expansion by Guichon, Liu and Thomas. We establish
the connection of our calculation with the generalized polarizabilities of the
nucleon where it is possible.Comment: 26 pages, 2 Postscript figures, RevTex using epsfi
Pion and Sigma Polarizabilities and Radiative Transitions
Fermilab E781 plans measurements of gamma-Sigma and -pion
interactions using a 600 GeV beam of Sigmas and pions, and a virtual photon
target. Pion polarizabilities and radiative transitions will be measured in
this experiment. The former can test a precise prediction of chiral symmetry;
the latter for a_1(1260) ----> pi + gamma is important for understanding the
polarizability. The experiment also measures polarizabilities and radiative
transitions for Sigma hyperons. The polarizabilities can test predictions of
baryon chiral perturbation theory. The radiative transitions to the
Sigma*(1385) provide a measure of the magnetic moment of the s-quark. Previous
experimental and theoretical results for gamma-pi and gamma-Sigma interactions
are given. The E781 experiment is described.Comment: 13 pages text (tex), Tel Aviv U. Preprint TAUP 2204-94, uses
Springer-Verlag TEX macro package lecproc.cmm (appended at end of tex file,
following \byebye), which requires extracting lecproc.cmm and putting this
file in your directory in addition to the tex file (mmcd.tex) before tex
processing. lecproc.cmm should be used following instructions and guidelines
available from Springer-Verlag. Submitted to the Proceedings of Workshop on
Chiral Dynamics, Massachusetts Institute of Technology, July 1994, Eds. A.
Bernstein, B. Holstein. Replaced Oct. 4 to add TAUP preprint number. Replaced
Oct. 12 to correct Pb target thickness from 1.3% interaction to 0.3
Recent Developments in Chiral Perturbation Theory
I review recent developments in chiral perturbation theory (CHPT) which is
the effective field theory of the standard model below the chiral symmetry
breaking scale. The effective chiral Lagrangian formulated in terms of the
pseudoscalar Goldstone bosons () is briefly discussed. It
is shown how one can gain insight into the ratios of the light quark masses and
to what extent these statements are model--independent. A few selected topics
concerning the dynamics and interactions of the Goldstone bosons are
considered. These are and scattering, some non--leptonic kaon
decays and the problem of strong pionic final state interactions. CHPT also
allows to make precise statements about the temperature dependence of QCD Green
functions and the finite size effects related to the propagation of the
(almost) massless pseudoscalar mesons. A central topic is the inclusion of
matter fields, baryon CHPT. The relativistic and the heavy fermion formulation
of coupling the baryons to the Goldstone fields are discussed. As applications,
photo--nucleon processes, the --term and non--leptonic hyperon
decays are presented. Implications of the spontaneously broken chiral symmetry
on the nuclear forces and meson exchange currents are also described. Finally,
the use of effective field theory methods in the strongly coupled Higgs sector
and in the calculation of oblique electroweak corrections is touched upon.Comment: TeX, 110 pages, 15 figures available upon request, BUTP-93/0