5,277 research outputs found
On the pion decay constant
The pion decay constant f_pi plays a crucial role in many areas of low energy
particle physics. Its value may e.g. be deduced from experimental data on
leptonic pion decays. Here, we provide comments on several aspects of this
evaluation. In particular, we point out that at the present level of
experimental accuracy, the value of f_pi is sensitive to the value of the pion
mass chosen in its chiral expansion.Comment: 15 pages, 3 figures. Accepted for publication in Phys. Lett.
The pi-N Sigma term - an evaluation using staggered fermions
A lattice calculation of the pi-N sigma term is described using dynamical
staggered fermions. Preliminary results give a sea term comparable in magnitude
to the valence term.Comment: Latex article, 3 pages. Contribution to the LAT93 Conference (Dallas,
U.S.A., September 1993). HLRZ preprint 93-7
Hadronic eta and eta-prime decays
The hadronic decays eta, eta-prime -> 3 pi and eta-prime -> eta pi pi are
investigated within the framework of U(3) chiral effective field theory in
combination with a relativistic coupled-channels approach. Final state
interactions are included by deriving s- and p-wave interaction kernels for
meson-meson scattering from the chiral effective Lagrangian and iterating them
in a Bethe-Salpeter equation. Very good overall agreement with currently
available data on decay widths and spectral shapes is achieved.Comment: 28 pages, 5 figures, 8 table
Finite size effects on in QCD from Chiral Perturbation Theory
We present a determination of the shift due to the finite
spatial box size by means of Chiral Perturbation Theory and
L\"uscher's formula. The range of applicability of the chiral prediction is
discussed.Comment: 3 pages, 3 figures, Lattice2002(spectrum
Integrating out the heaviest quark in N--flavour ChPT
We extend a known method to integrate out the strange quark in three flavour
chiral perturbation theory to the context of an arbitrary number of flavours.
As an application, we present the explicit formulae to one--loop accuracy for
the heavy quark mass dependency of the low energy constants after decreasing
the number of flavours by one while integrating out the heaviest quark in
N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ
Threshold Photo/Electro Pion Production - Working Group Summary
We summarize the pertinent experimental and theoretical developments in the
field of pion photo- and electroproduction in the threshold region. We discuss
which experiments and which calculations should be done/performed in the
future.Comment: plain TeX (macro included), 6pp, summary talk presented at the
workshop on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints
Constraints on the parameters in the one- and two-loop pion-pion scattering
amplitudes of standard chiral perturbation theory are obtained from explicitly
crossing-symmetric sum rules. These constraints are based on a matching of the
chiral amplitudes and the physical amplitudes at the symmetry point of the
Mandelstam plane. The integrals over absorptive parts appearing in the sum
rules are decomposed into crossing-symmetric low- and high-energy components
and the chiral parameters are finally related to high-energy absorptive parts.
A first application uses a simple model of these absorptive parts. The
sensitivity of the results to the choice of the energy separating high and low
energies is examined with care. Weak dependence on this energy is obtained as
long as it stays below ~560 MeV. Reliable predictions are obtained for three
two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of
RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical
corrections including the number at the end of the abstract, two sentences
added at the end of Section 5 in answer to a referee's remar
Four-pion production
Starting from the low-energy structure derived from QCD, we extend the
amplitudes for four-pion production in e+ e- annihilation and tau decays up to
invariant four-pion masses of 1 GeV. Cross sections and branching ratios
BR(rho^0 -> 4 pi) are compared with available data.Comment: 4 pages, 3 figures, contribution to Proc. of QCD'02, Montpellier,
July 2002, misprints correcte
Instability of Amorphous Ru-Si-O Thin Films under Thermal Oxidation
Ternary films about 200 nm thick of composition Ru20Si15O65 have been synthesized by reactive rf magnetron sputtering of a Ru1Si1 target in an argon-oxygen gas. As-deposited, the films are X-ray-amorphous. Their atomic density is 8.9 × 10^22/cm^3 (5.1 g/cm^3), and their electrical resistivity is in the range of 2 mOmega cm. After annealing in dry oxygen at 600°C for 30 min, micron-sized grains of RuO2 grow out of the film and volatile RuO4 escapes. The significance of these results is discussed
Soldiers, civilians and peacekeeping – evidence and false assumptions
The assumption that peacekeeping requires soldiers carrying weapons is widespread; 35 years of successful peacekeeping by unarmed civilians is often overlooked. The original definition of peacekeeping is being confused with peace enforcement and peace operations. Limited interest has led to underfunding of unarmed civilian peacekeeping (UCP) with fewer resources for both study and praxis. Marginalization of civilian peacekeeping has restricted the options for complex interventions; this reduced vision of peacekeeping is open to challenge in the light of evidence from the field. This paper first examines what is meant by peacekeeping and UCP. The relationship of UCP to nonviolence, feminism, and peace studies is considered. The constraints and limits of peacekeeping by armed military personnel during, or after, violent conflict are outlined. The core tasks of peacekeeping are analysed, and evidence from the field is presented to show that these core tasks can be (and have been) successfully undertaken by unarmed civilians for three decades, world-wide. The argument that armed military personnel are necessary, even essential, for peacekeeping is not supported by the evidence of civilian success in undertaking the core tasks. The paper ends with conclusions and a call for a new paradigm for peacekeeping
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