39 research outputs found
Baryon-Baryon Interactions
After a short survey of some topics of interest in the study of baryon-baryon
scattering, the recent Nijmegen energy dependent partial wave analysis (PWA) of
the nucleon-nucleon data is reviewed. In this PWA the energy range for both pp
and np is now 0 < Tlab < 350 MeV and a chi^2_{d.o.f.}=1.08 was reached. The
implications for the pion-nucleon coupling constants are discussed. Comments
are made with respect to recent discussions around this coupling constant in
the literature. In the second part, we briefly sketch the picture of the baryon
in several, more or less QCD-based, quark-models that have been rather
prominent in the literature. Inspired by these pictures we constructed a new
soft-core model for the nucleon-nucleon interaction and present the first
results of this model in a chi^2 -fit to the new multi-energy Nijmegen PWA.
With this new model we succeeded in narrowing the gap between theory and
experiment at low energies. For the energies Tlab = 25-320 MeV we reached a
record low chi^2_{p.d.p.} = 1.16. We finish the paper with some conclusions and
an outlook describing the extension of the new model to baryon-baryon
scattering.Comment: 12 pages LaTeX and one postscript figure included. Invited talk
presented at the XIVth European Conference of Few-Body Problems in Physics,
Amsterdam, August 23-28, 199
Strange two-baryon interactions using chiral effective field theory
We have constructed the leading order strangeness S=-1,-2 baryon-baryon
potential in a chiral effective field theory approach. The chiral potential
consists of one-pseudoscalar-meson exchanges and non-derivative four-baryon
contact terms. The potential, derived using SU(3)_f symmetry constraints,
contains six independent low-energy coefficients. We have solved a regularized
Lippmann-Schwinger equation and achieved a good description of the available
scattering data. Furthermore a correctly bound hypertriton has been obtained.Comment: 3 pages, 2 PostScript figures, talk to appear in the proceedings of
the "20th European Conference on Few-Body Problems in Physics (EFB20), Pisa,
Italy, 10-14 September 2007
Hyperon interaction with dense nuclear matter and link to neutron stars
The theoretical status of the hyperon-nucleon and hyperon-hyperon
interactions is reviewed, paying a special attention to chiral effective field
theories. Results on hyperons in dense matter are presented and the
consequences for the properties of neutron stars are analyzed.Comment: 6 pages, 2 figures, invited plenary talk, published In: Elia D.,
Bruno G.E., Colangelo P., Cosmai L. (eds). The XVIII International Conference
on Strangeness in Quark Matter (SQM 2019
Roy-Steiner equations for pion-nucleon scattering
Starting from hyperbolic dispersion relations, we derive a closed system of
Roy-Steiner equations for pion-nucleon scattering that respects analyticity,
unitarity, and crossing symmetry. We work out analytically all kernel functions
and unitarity relations required for the lowest partial waves. In order to
suppress the dependence on the high-energy regime we also consider once- and
twice-subtracted versions of the equations, where we identify the subtraction
constants with subthreshold parameters. Assuming Mandelstam analyticity we
determine the maximal range of validity of these equations. As a first step
towards the solution of the full system we cast the equations for the
partial waves into the form of a Muskhelishvili-Omn\`es
problem with finite matching point, which we solve numerically in the
single-channel approximation. We investigate in detail the role of individual
contributions to our solutions and discuss some consequences for the spectral
functions of the nucleon electromagnetic form factors.Comment: 106 pages, 18 figures; version published in JHE
Viable Tumor Tissue Adherent to Needle Applicators after Local Ablation: A Risk Factor for Local Tumor Progression
Background. Local tumor progression (LTP) is a serious complication after local ablation of malignant liver tumors, negatively influencing patient survival. LTP may be the result of incomplete ablation of the treated tumor. In this study, we determined whether viable tumor cells attached to the needle applicator after ablation was associated with LTP and disease-free survival. Methods. In this prospective study, tissue was collected of 96 consecutive patients who underwent local liver ablations for 130 liver malignancies. Cells and tissue attached to the needle applicators were analyzed for viability using glucose-6-phosphate-dehydrogenase staining and autofluorescence intensity levels of H&E stained sections. Patients were followed-up until disease progression. Results. Viable tumor cells were found on the needle applicators after local ablation in 26.7% of patients. The type of needle applicator used, an open approach, and the omission of track ablation were significantly correlated with viable tumor tissue adherent to the needle applicator. The presence of viable cells was an independent predictor of LTP. The attachment of viable cells to the needle applicators was associated with a shorter time to LTP. Conclusions. Viable tumor cells adherent to the needle applicators were found after ablation of 26.7% of patients. An independent risk factor for viable cells adherent to the needle applicators is the omission of track ablation. We recommend using only RFA devices that have track ablation functionality. Adherence of viable tumor cells to the needle applicator after local ablation was an independent risk factor for LT
Human Fertility, Molecular Genetics, and Natural Selection in Modern Societies
Research on genetic influences on human fertility outcomes such as number of children ever born (NEB) or the age at first childbirth (AFB) has been solely based on twin and family-designs that suffer from problematic assumptions and practical limitations. The current study exploits recent advances in the field of molecular genetics by applying the genomic-relationship-matrix based restricted maximum likelihood (GREML) methods to quantify for the first time the extent to which common genetic variants influence the NEB and the AFB of women. Using data from the UK and the Netherlands (N = 6,758), results show significant additive genetic effects on both traits explaining 10% (SE = 5) of the variance in the NEB and 15% (SE = 4) in the AFB. We further find a significant negative genetic correlation between AFB and NEB in the pooled sample of –0.62 (SE = 0.27, p-value = 0.02). This finding implies that individuals with genetic predispositions for an earlier AFB had a reproductive advantage and that natural selection operated not only in historical, but also in contemporary populations. The observed postponement in the AFB across the past century in Europe contrasts with these findings, suggesting an evolutionary override by environmental effects and underscoring that evolutionary predictions in modern human societies are not straight forward. It emphasizes the necessity for an integrative research design from the fields of genetics and social sciences in order to understand and predict fertility outcomes. Finally, our results suggest that we may be able to find genetic variants associated with human fertility when conducting GWAS-meta analyses with sufficient sample size
Scalar-meson-baryon coupling constants in QCD sum rules
The external-field QCD Sum Rules method is used to evaluate the coupling
constants of the light-isoscalar scalar meson (``\sigma'' or \epsilon) to the
\Lambda, \Sigma, and \Xi baryons. It is shown that these coupling constants as
calculated from QCD Sum Rules are consistent with SU(3)-flavor relations, which
leads to a determination of the F/(F+D) ratio of the scalar octet assuming
ideal mixing: we find \alpha_s \equiv F/(F+D)=0.55. The coupling constants with
SU(3) breaking effects are also discussed.Comment: 15 pages, 8 figures, to be published in Phys. Rev.
ANTIPROTON-PROTON PARTIAL-WAVE ANALYSIS BELOW 925 MEV/C
A partial-wave analysis of all ppBAR scattering data below 925 MeV/c antiproton laboratory momentum is presented. The method used is adapted from the Nijmegen phase-shift analyses of pp and np scattering data. We solve the Schrodinger equation for the coupled ppBAR and nnBAR channels where the long- and intermediate-range interactions are described by a theoretically well-founded potential. This gives the rapid variations of the scattering amplitudes with energy. This potential consists of the Coulomb potential with the main relativistic correction, the magnetic-moment interaction, the one-pion-exchange potential, and the heavy-boson exchanges of the Nijmegen one-boson-exchange potential. Slow variations of the amplitudes due to short-range interactions, including the coupling to mesonic annihilation channels, are parametrized by an energy-dependent, complex boundary condition, specified at a radius of r = 1.3 fm. The Nijmegen 1993 ppBAR database, consisting of 3646 ppBAR scattering data, is presented and discussed. The best fit to this database results in chi(min)2/N(data) = 1.043. This good fit to the data shows that the Nijmegen long- and intermediate-range potential is essentially correct. The pseudovector coupling constant of the charged pion to nucleons is determined to be f(c)2 = 0.0732(11) at the pion pole, where the error is statistical