3,242 research outputs found
One loop corrections to quantum hadrodynamics with vector mesons
The renormalized elastic scattering amplitude to one loop is
calculated in the chiral limit in the model and in a Quantum
Hadrodynamic model (QHD-III) with vector mesons. It is argued that QHD-III
reduces to the linear model in the limit that the vector meson masses
become large. The pion decay constant is also calculated to 1-loop in the
model, and at tree level in QHD-III; it is shown that the coefficient
of the tree level term in the scattering amplitude equals . The
1-loop correction of in QHD-III violates strong isospin current
conservation. Thus,it is concluded that QHD-III can, at best, only describe the
strongly interacting nuclear sector.Comment: 6 page
Long distance contribution to decay and terms in CHPT
The long distance contribution to is
calculated using chiral perturbation theory. The leading contribution comes
from tree terms. The branching ratio of the long distance
contribution is found to be of order smaller than the short distance
contributions.Comment: 12 pages, 1 figure (available upon request
Rationales for the Bernese approaches in acetabular surgery
Purpose: To present two new approaches to acetabular surgery that were established in Berne, and which aim at enhanced visualization and anatomical reconstruction of acetabular fractures. Method: The trochanteric flip osteotomy allows for surgical hip dislocation, and was introduced as a posterior approach for acetabular fracture management involving the posterior column and wall. For acetabular fractures predominantly involving the anterior column and the quadrilateral plate, the Pararectus approach is described. Results: Full exposure of the hip joint, as provided by the trochanteric flip osteotomy, facilitates anatomical reduction of acetabular or femoral head fractures and safe positioning of the anterior column screw in transverse or T-shaped fractures. Additionally, the approach enables osteochondral transplantation as a salvage procedure for severe chondral femoral head damage and osteoplasty of an associated inadequate offset at the femoral head-neck junction. The Pararectus approach allows anatomical restoration with minimal access morbidity, and combines advantages of the ilioinguinal and modified Stoppa approaches. Conclusions: Utilization of the trochanteric flip osteotomy eases visualization of the superior aspect of the acetabulum, and enables the evaluation and treatment of chondral lesions of the femoral head or acetabulum and labral tears. Displaced fractures of the anterior column with a medialized quadrilateral plate can be addressed successfully through the Pararectus approach, in which surgical access is associated with minimal morbidity. However, long-term results following the two presented Bernese approaches are needed to confirm that in the treatment of complex acetabular fractures the rate of poor results in almost one-third of all cases (as currently yielded using traditional approaches) might be reduced by the utilization of the presented novel approache
Role of Scalar Meson Resonances in $K_{L}^{0} \rightarrow \pi^{0} \gamma \gamma Decay
Corrections to decay induced by
scalar meson exchange are studied within chiral perturbation theory. In spite
of bad knowledge of scalar-mesons parameters, the calculated branching ratio
can be changed by a few percent.Comment: 18 pages of text, 2 figures (available upon request); preprint
IJS-TP-16-94 , TUM-T31-63-94
Tensor meson exchange at low energies
We complete the analysis of meson resonance contributions to chiral
low-energy constants of O(p^4) by including all quark-antiquark bound states
with orbital angular momentum less or equal to one. Different tensor meson
Lagrangians used in previous work are shown to produce the same final results
for the low-energy constants once QCD short-distance constraints are properly
implemented. We also discuss the possible relevance of axial-vector mesons with
odd C-parity.Comment: 20 pages, comparison with previous work updated, typos removed,
results unchanged, version to appear in EPJ
Mean Curvature Flow of Spacelike Graphs
We prove the mean curvature flow of a spacelike graph in of a map from a closed Riemannian
manifold with to a complete Riemannian manifold
with bounded curvature tensor and derivatives, and with
sectional curvatures satisfying , remains a spacelike graph,
exists for all time, and converges to a slice at infinity. We also show, with
no need of the assumption , that if , or if and
, constant, any map is trivially
homotopic provided where
, in case , and
in case . This largely extends some known results for
constant and compact, obtained using the Riemannian structure
of , and also shows how regularity theory on the mean
curvature flow is simpler and more natural in pseudo-Riemannian setting then in
the Riemannian one.Comment: version 5: Math.Z (online first 30 July 2010). version 4: 30 pages:
we replace the condition by the the weaker one .
The proofs are essentially the same. We change the title to a shorter one. We
add an applicatio
Isospin violation and the proton's neutral weak magnetic form factor
The effects of isospin violation on the neutral weak magnetic form factor of
the proton are studied using two-flavour chiral perturbation theory. The first
nonzero contributions appear at O(p^4) in the small-momentum expansion, and the
O(p^5) corrections are also calculated. The leading contributions from an
explicit Delta(1232) isomultiplet are included as well. At such a high order in
the chiral expansion, one might have expected a large number of unknown
parameters to contribute. However, it is found that no unknown parameters can
appear within loop diagrams, and a single tree-level counterterm at O(p^4) is
sufficient to absorb all divergences. The momentum dependence of the neutral
weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure
On the Hadronic Contribution to Light-by-light Scattering in
We comment on the theoretical uncertainties involved in estimating the
hadronic effects on the light-by-light scattering contribution to the anomalous
magnetic moment of the muon, especially based on the analysis and results of T.
Kinoshita, B. Ni\v zi\'c, and Y. Okamoto, Phys.\ Rev.\ D31, 2108 (1985). From
the point of view of an effective field theory and chiral perturbation theory,
we suggest that the charged pion contribution may be better determined than has
been appreciated. However, the neutral pion contribution needs greater
theoretical insight before its magnitude can be reliably estimated.Comment: 9 pages, no figures, U. Michigan UM-TH-93-18. (Input phyzzm to
compile.) Revised version has minor changes in text. To be published in Phys.
Rev. D, Comments sectio
Muon capture by a proton in heavy baryon chiral perturbation theory
The matrix element for muon capture by a proton is calculated to O(p^3)
within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian
of Ecker and Mojzis. External nucleon fields are renormalized using the
appropriate definition of the wave function renormalization factor Z_N. Our
expression for Z_N differs somewhat from that found in existing literature, but
is the one which is consistent with the Lagrangian we use and the one which
ensures, within our approach, the nonrenormalization of the vector coupling as
required by the conserved vector current. Expressions for the standard muon
capture form factors are derived and compared to experimental data and we
determine three of the coefficients of the Ecker - Mojzis Lagrangian, namely,
b_7, b_{19}, and b_{23}.Comment: 14 pages, LaTeX, using revte
Vector meson couplings to vector and tensor currents in extended NJL quark model
A simple explanation of the dynamic properties of vector mesons is given in
the framework of extended Nambu - Jona-Lasinio quark model. New mass relations
among the hadron vector resonances are derived. The results of this approach
are in good accordance with the QCD sum rules, the lattice calculations and the
experimental data.Comment: 4 pages, 2 figure
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