73 research outputs found
Magnetic moment of the Roper resonance
The magnetic moment of the Roper resonance is calculated in the framework of
a low-energy effective field theory of the strong interactions. A systematic
power-counting procedure is implemented by applying the complex-mass scheme.Comment: 13 pages, 4 figure
Complex-mass scheme and perturbative unitarity
We derive cutting rules for loop integrals containing propagators with
complex masses. Using a field-theoretical model of a heavy vector boson
interacting with a light fermion, we demonstrate that the complex-mass scheme
respects unitarity order by order in a perturbative expansion provided that the
renormalized coupling constant remains real.Comment: Accepted for publication in International Journal of Modern Physics
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
Axial, induced pseudoscalar, and pion-nucleon form factors in manifestly Lorentz-invariant chiral perturbation theory
We calculate the nucleon form factors G_A and G_P of the isovector
axial-vector current and the pion-nucleon form factor G_piN in manifestly
Lorentz-invariant baryon chiral perturbation theory up to and including order
O(p^4). In addition to the standard treatment including the nucleon and pions,
we also consider the axial-vector meson a_1 as an explicit degree of freedom.
This is achieved by using the reformulated infrared renormalization scheme. We
find that the inclusion of the axial-vector meson effectively results in one
additional low-energy coupling constant that we determine by a fit to the data
for G_A. The inclusion of the axial-vector meson results in an improved
description of the experimental data for G_A, while the contribution to G_P is
small.Comment: 21 pages, 9 figures, REVTeX
Infrared renormalization of two-loop integrals and the chiral expansion of the nucleon mass
We describe details of the renormalization of two-loop integrals relevant to
the calculation of the nucleon mass in the framework of manifestly
Lorentz-invariant chiral perturbation theory using infrared renormalization. It
is shown that the renormalization can be performed while preserving all
relevant symmetries, in particular chiral symmetry, and that renormalized
diagrams respect the standard power counting rules. As an application we
calculate the chiral expansion of the nucleon mass to order O(q^6).Comment: Version accepted for publication in Nucl. Phys. A, missing one-loop
diagram added, minor changes in notation, discussion of results improve
Is Heavy Baryon Approach Necessary?
It is demonstrated that using an appropriately chosen renormalization
condition one can respect power counting within the relativistic baryon chiral
perturbation theory without appealing to the technique of the heavy baryon
approach. Explicit calculations are performed for diagrams including two-loops.
It is argued that the introduction of the heavy baryon chiral perturbation
theory was useful but not necessary.Comment: 9 pages, 2 figures, minor changes, references adde
Mass and width of the Roper resonance using complex-mass renormalization
The pole mass and the width of the Roper resonance are calculated as
functions of the pion mass in the framework of low-energy effective field
theory of the strong interactions. We implement a systematic power-counting
procedure by applying the complex-mass renormalization scheme.Comment: 8 pages, 2 fugures, REVTeX
Baryon masses and nucleon sigma terms in manifestly Lorentz-invariant baryon chiral perturbation theory
We discuss the masses of the ground state baryon octet and the nucleon sigma
terms in the framework of manifestly Lorentz-invariant baryon chiral
perturbation theory. In order to obtain a consistent power counting for
renormalized diagrams the extended on-mass-shell renormalization scheme is
applied.Comment: 18 pages, 3 figures, accepted for publication in J. Phys.
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