3,849 research outputs found
Symmetry Problems in Low Energy Physics
Some recent experimental and theoretical work on 1) charge symmetry-breaking,
2) parity non-conservation, and 3) searches for breaking of time reversal
invariance are reviewed. The examples illustrate the uses of symmetry to learn
about underlying dynamics and/or structure.Comment: 15 pages, tex, figures available from
[email protected] Talk presented at WEIN'9
Isospin Splitting in the Pion-Nucleon Couplings from QCD Sum Rules
We use QCD sum rules for the three point function of a pseudoscalar and two
nucleonic currents in order to estimate the charge dependence of the pion
nucleon coupling constant coming from isospin violation in the strong
interaction. The effect can be attributed primarily to the difference of the
quark condensates and . Assuming that the pi0 is a pure
isostate we obtain for the splitting between the coupling of proton and neutron
to the neutral pion an interval of [0.008 ; 0.023], the uncertainties coming
mainly from the input parameters. In order to obtain the coupling to a physical
pi0 we have to take pi - eta mixing into account leading to an interval of
[0.012 ; 0.037]. The charged pion nucleon coupling is found to be the average
of the two neutral ones. Electromagnetic effects are not included.Comment: contributed talk at CIPANP97 (Big Sky, Montana); 3 pages
(aipproc.sty), no figure
Axial current matrix elements and pentaquark decay widths in chiral soliton models
Here I explain why in chiral soliton models the hadronic transition operator
of the pentaquark decay cannot be identified from the axial current.Comment: seven pages, note on Delta resonance added, refs updated, version to
be published in PR
Temperature-dependent "phason" elasticity in a random tiling quasicrystal
Both ``phason'' elastic constants have been measured from Monte Carlo
simulations of a random-tiling icosahedral quasicrystal model with a
Hamiltonian. The low-temperature limit approximates the ``canonical-cell''
tiling used to describe several real quasicrystals. The elastic constant K2
changes sign from positive to negative with decreasing temperature; in the
``canonical-cell'' limit, K2/K1 appears to approach -0.7, about the critical
value for a phason-mode modulation instability. We compare to the experiments
on i-AlPdMn and i-AlCuFe.Comment: 5 pages, 2 Postscript figures, LaTeX, uses revtex4, submitted to PR
Neutrino Properties, Cosmology
Review of neutrino properties; double beta decay; very high energy neutrinos;
leptogenesisComment: 10 pages, 3 figures; conference tal
Mesons and the Structure of Nucleons
The role of mesons, particularly the pion, in the structure of nucleons is
reviewed and investigated. Since quark-antiquark pairs are likely to
``transform" into mesons at large distances, mesons are expected to contribute
to nucleon structure. Their effects on the Gottfried sum rule, on the
strangeness content of the nucleon, and on the spin of the nucleon are
discussed.Comment: 15 pages, TeX file followed by 3 uuencoded PostScript figures
(optional), DOE/ER/40427-08-N9
Combined energy -- diffraction data refinement of decagonal AlNiCo
We incorporate realistic pair potential energies directly into a non-linear
least-square fit of diffraction data to quantitatively compare structure models
with experiment for the Ni-rich (AlNiCo) quasicrystal. The initial structure
models are derived from a few {\it a priori} assumptions (gross features of the
Patterson function) and the pair potentials. In place of the common hyperspace
approach to the structure refinement of quasicrystals, we use a real-space tile
decoration scheme, which does not rely on strict quasiperiodicity, and makes it
easy to enforce sensible local arrangements of the atoms. Inclusion of the
energies provides information complementary to the diffraction data and
protects the fit procedure from converging on spurious solutions. The method
pinpoints sites which are likely to break the symmetry of their local
environment.Comment: 7 pages, 5 figures, proceedings of the Internation Conference on
Quasicrystals, Bangalore, India, August 200
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