8,582 research outputs found
Generalized Polarizabilities in a Constituent Quark Model
We discuss low-energy virtual Compton scattering off the proton within the
framework of a nonrelativistic constituent quark model. A simple interpretation
of the spin-averaged generalized polarizabilities is given in terms of the
induced electric polarization (and magnetization). Explicit predictions for the
generalized polarizabilities obtained from a multipole expansion are presented
for the Isgur-Karl model and are compared with results of various models.Comment: 10 pages, Latex, 2 figures, uses ws-p8-50x6-00.cls, talk given at
NSTAR2001, Workshop on "The Physics of Excited Nucleons," Mainz, Germany,
March 7-10, 200
Pion polarizabilities: No conflict between dispersion theory and ChPT
Recent attempts to determine the pion polarizability by dispersion relations
yield values that disagree with the predictions of chiral perturbation theory.
These dispersion relations are based on specific forms for the absorptive part
of the Compton amplitudes. The analytic properties of these forms are examined,
and the strong enhancement of intermediate-meson contributions is shown to be
connected to non-analytic structuresComment: 9 pages, 4 figures; Proceedings of 6th International Workshop on
Chiral Dynamics, 6-10 July 2009, Bern, Switzerlan
Path integral quantization for massive vector bosons
A parity-conserving and Lorentz-invariant effective field theory of
self-interacting massive vector fields is considered. For the interaction terms
with dimensionless coupling constants the canonical quantization is performed.
It is shown that the self-consistency condition of this system with the
second-class constraints in combination with the perturbative renormalizability
leads to an SU(2) Yang-Mills theory with an additional mass term.Comment: 16 pages, 2 figures, REVTeX
Complex mass renormalization in EFT
We consider an effective field theory of unstable particles (resonances)
using the complex-mass renormalization. As an application we calculate the
masses and the widths of the meson and the Roper resonance.Comment: 8 pages, 2 figures; Proceedings of 6th International Workshop on
Chiral Dynamics, 6-10 July 2009, Bern, Switzerlan
Improving the ultraviolet behavior in baryon chiral perturbation theory
We introduce a new formulation of baryon chiral perturbation theory which
improves the ultraviolet behavior of propagators and can be interpreted as a
smooth cutoff regularization scheme. It is equivalent to the standard approach,
preserves all symmetries and therefore satisfies the Ward identities. Our
formulation is equally well defined in the vacuum, one- and few-nucleon sectors
of the theory. The equations (Bethe-Salpeter, Lippmann-Schwinger, etc.) for the
scattering amplitudes of the few-nucleon sector are free of divergences in the
new approach. Unlike the usual cutoff regularization, our 'cutoffs' are
parameters of the Lagrangian and do not have to be removed.Comment: 19 pages, 3 figures, REVTeX 4; version to be published in Phys. Rev.
D, additional section on issues of renormalization in few-body sector
include
Chiral expansion of the nucleon mass to order q^6
We present the results of a complete two-loop calculation at order q^6 of the
nucleon mass in manifestly Lorentz-invariant chiral perturbation theory. The
renormalization is performed using the reformulated infrared renormalization,
which allows for the treatment of two-loop integrals while preserving all
relevant symmetries, in particular chiral symmetry.Comment: 6 pages, 2 figures, REVTeX
Complex-mass scheme and resonances in EFT
The complex-mass scheme (CMS) provides a consistent framework for dealing
with unstable particles in quantum field theory and has been successfully
applied to various loop calculations. As applications of the CMS in chiral
effective field theory we consider the form factor of the pion in the time-like
region and the magnetic moment of the Roper resonance.Comment: 4 pages, 2 figures, contribution to the workshop NSTAR 201
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