163 research outputs found
Nucleon mass, sigma term and lattice QCD
We investigate the quark mass dependence of the nucleon mass M_N. An
interpolation of this observable, between a selected set of fully dynamical
two-flavor lattice QCD data and its physical value, is studied using
relativistic baryon chiral perturbation theory up to order p^4. In order to
minimize uncertainties due to lattice discretization and finite volume effects
our numerical analysis takes into account only simulations performed with
lattice spacings a5. We have also restricted ourselves to
data with m_pi<600 MeV and m_sea=m_val. A good interpolation function is found
already at one-loop level and chiral order p^3. We show that the
next-to-leading one-loop corrections are small. From the p^4 numerical analysis
we deduce the nucleon mass in the chiral limit, M_0 approx 0.88 GeV, and the
pion-nucleon sigma term sigma_N= (49 +/- 3) MeV at the physical value of the
pion mass.Comment: 12 pages, 4 figures, revised journal versio
Chiral 3-exchange NN-potentials: Results for dominant next-to-leading order contributions
We calculate in (two-loop) chiral perturbation theory the local NN-potentials
generated by the three-pion exchange diagrams with one insertion from the
second order chiral effective pion-nucleon Lagrangian proportional to the
low-energy constants . The resulting isoscalar central potential
vanishes identically. In most cases these -exchange potentials are larger
than the ones generated by the diagrams involving only leading order vertices
due to the large values of (which mainly represent virtual
-excitation). A similar feature has been observed for the chiral
-exchange. We also give suitable (double-integral) representations for
the spin-spin and tensor potentials generated by the leading-order diagrams
proportional to involving four nucleon propagators. In these cases the
Cutkosky rule cannot be used to calculate the spectral-functions in the
infinite nucleon mass limit since the corresponding mass-spectra start with a
non-vanishing value at the -threshold. Altogether, one finds that chiral
-exchange leads to small corrections in the region fm where
- and chiral -exchange alone provide a very good strong NN-force as
shown in a recent analysis of the low-energy pp-scattering data-base.Comment: 11 pages, 7 figures, to be published in The Physical Review
Bethe-Salpeter Approach for the Elastic Pion-Nucleon Scattering in Heavy Baryon Chiral Perturbation Theory
Heavy Baryon Chiral Perturbation Theory (HBChPT) to leading order provides a
kernel to solve the Bethe-Salpeter equation for the
(-channel) system, in the infinite nucleon mass limit.
Crossed Born terms include, when iterated within the Bethe-Salpeter equation,
both {\it all} one- and {\it some} two-pion intermediate states, hence
preserving elastic unitarity below the two-pion production threshold. This
suggests searching for a solution with the help of dispersion relations and
suitable subtraction constants, when all in-elasticities are explicitly
neglected. The solution allows for a successful description of the experimental
phase shift from threshold up to MeV in terms of four
subtraction constants. Next-to-leading order HBChPT calculations are also used
to estimate the unknown subtraction constants which appear in the solution.
Large discrepancies are encountered which can be traced to the slow convergence
rate of HBChPT.Comment: 11 pages, 3 figure
Towards an understanding of isospin violation in pion-nucleon scattering
We investigate isospin breaking in low-energy pion-nucleon scattering in the
framework of chiral perturbation theory. This work extends the systematic
analysis of [1] to the energy range above threshold. Various relations, which
identically vanish in the limit of isospin symmetry, are used to quantify
isospin breaking effects. We study the energy dependence of the S- and P-wave
projections of these ratios and find dramatic effects in the S-waves of those
two relations which are given in terms of isoscalar quantities only. This
effect drops rather quickly with growing center-of-mass energy.Comment: 12 pp, REVTeX, 8 figs, FZJ-IKP(TH)-2000-2
Baryon chiral perturbation theory with virtual photons and leptons
We construct the general pion-nucleon SU(2) Lagrangian including both virtual
photons and leptons for relativistic baryon chiral perturbation theory up to
fourth order. We include the light leptons as explicit dynamical degrees of
freedom by introducing new building blocks which represent these leptons.Comment: 11 page
Chiral -exchange NN-potentials: Two-loop contributions
We calculate in heavy baryon chiral perturbation theory the local
NN-potentials generated by the two-pion exchange diagrams at two-loop order. We
give explicit expressions for the mass-spectra (or imaginary parts) of the
corresponding isoscalar and isovector central, spin-spin and tensor
NN-amplitudes. We find from two-loop two-pion exchange a sizeable isoscalar
central repulsion which amounts to MeV at fm. There is a
similarly strong isovector central attraction which however originates mainly
from the third order low energy constants entering the chiral -scattering amplitude. We also evaluate the one-loop -exchange diagram
with two second order chiral -vertices proportional to the low
energy constants as well as the first relativistic 1/M-correction
to the -exchange diagrams with one such vertex. The diagrammatic results
presented here are relevant components of the chiral NN-potential at
next-to-next-to-next-to-leading order.Comment: 6 pages, 2 figure
The (1535) and (1650) Resonances in Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory
The wave meson-baryon scattering is analyzed for the strangeness S=0
sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral
Symmetry. Four channels have been considered: , , ,
. The needed two particle irreducible matrix amplitude is taken from
lowest order Chiral Perturbation Theory in a relativistic formalism and low
energy constants are fitted to the elastic phase-shifts and the and cross section data. The position of
the complex poles in the second Riemann sheet of the scattering amplitude
determine masses and widths of the (1535) and (1650)
resonances, in reasonable agreement with experiment. A good overall description
of data, from threshold up to 2 GeV, is achieved keeping in mind that
the two pion production channel has not been included.Comment: 35 pages, LaTeX + 7 ps-figure files. Some minor mistakes have been
corrected for and a new appendix discussing the matching to HBChPT has been
also adde
Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory and the (1405) and (1670) Resonances
The wave meson-baryon scattering is analyzed for the strangeness
and isospin I=0 sector in a Bethe-Salpeter coupled channel formalism
incorporating Chiral Symmetry. Four channels have been considered: , , and . The required input to solve
the Bethe-Salpeter equation is taken from lowest order Chiral Perturbation
Theory in a relativistic formalism. There appear undetermined low energy
constants, as a consequence of the renormalization of the amplitudes, which are
obtained from fits to the mass-spectrum, to the elastic
and --matrices and to the
cross section data. The position and residues of the
complex poles in the second Riemann Sheet of the scattering amplitude determine
masses, widths and branching ratios of the (1405) and
(1670) resonances, in reasonable agreement with experiment. A good
overall description of data, from threshold up to 1.75 GeV, is
achieved despite the fact that three-body channels have not been explicitly
included.Comment: 23 pages, Latex, 10 Figures. In this revised version a new subsection
3.6 on Heavy Baryon Expansion and new references have been adde
Recommended from our members
Disability in Basic Activities of Daily Living Is Associated With Symptom Burden in Older People With Advanced Cancer or Chronic Obstructive Pulmonary Disease: A Secondary Data Analysis.
CONTEXT: Managing activities of daily living is important to people with advanced cancer or chronic obstructive pulmonary disease (COPD). Understanding disability in activities of daily living may inform service planning. OBJECTIVE: To identify the prevalence of disability in activities of daily living, associations and change over time, in older people with advanced cancer or COPD. METHODS: Secondary analysis of International Access, Rights and Empowerment (IARE) studies in adults aged ≥65 years with advanced disease in the United Kingdom, Ireland, and United States, using cross-sectional (IARE I & II) and longitudinal (IARE II, 3 timepoints over 6 months) data. Measures included disability in activities of daily living (Barthel Index), symptom severity (Palliative Outcome Scale), and assistive device use (self-reported). Logistic regression was used to identify relationships between disability and age, sex, living alone, diagnosis, and symptom burden; visual graphical analysis explores individual disability trajectories. RESULTS: One hundred fifty-nine participants were included (140 cancer, 19 COPD). Sixty-five percent had difficulty climbing stairs, 48% bathing, 39% dressing, and 36% mobilizing. Increased disability was independently associated with increased symptom burden (odds ratio, 1.08 [95% CI:1.02-1.15], P = 0.01) and walking unaided (z = 2.35, P = 0.02), but not with primary diagnosis (z = -0.47, P = 0.64). Disability generally increased over time but with wide interindividual variation. CONCLUSION: Disability in activities of daily living in advanced cancer or COPD is common, associated with increased symptom burden, and may be attenuated by use of assistive devices. Individual disability trajectories vary widely, with diverse disability profiles. Services should include rehabilitative interventions, guided by disability in individual activities of daily living
- …