5,812 research outputs found
Meson-Nucleon Vertex Form Factors at Finite Temperature Using a Soft Pion Form Factor
The temperature and density dependence of the meson-nucleon vertex form
factors is studied in the framework of thermofield dynamics. Results are
obtained for two rather different nucleon-nucleon potentials: the usual Bonn
potential and the variation with a softer form factor, due to Holinde
and Thomas. In general, the results show only a modest degree of sensitivity to
the choice of interaction.Comment: 5 pages, uses revtex
A test of the instanton vacuum chiral quark model with axial anomaly low-energy theorems
The QCD + QED axial anomaly low-energy theorems are applied to estimate the
accuracy of an instanton vacuum - based chiral quark model. The low-energy
theorems give an exact relation between the matrix elements of the gluon and
photon parts of the QCD + QED axial anomaly operator equation. The matrix
elements between vacuum and two photon states and between vacuum and two gluon
states are calculated for arbitrary N_f. It is shown that this model does
satisfy the low-energy theorems with an accuracy of . We estimate
also the contribution of the nonperturbative conversion of gluons into photons
to the decay and compare with experimental data.Comment: uudecode, gzip, latex, 11 pages, the text and the list of references
was slightly change
First-principles study of the onset of noncollinearity in Mnn clusters: Magnetic arrangements in Mn5 and Mn6
First-principles theoretical investigations of the noncollinearity of atomic spin moments in manganese clusters have been carried out within a gradient-corrected density-functional approach. Our studies on Mn5 and Mn6 include investigation of both collinear and noncollinear arrangements. It is shown that while the atomic structure of the ground state of Mn5 is a triangular bipyramid, the collinear and noncollinear arrangements have comparable energies and hence are degenerate. For Mn6, while the ground state has a square bipyramid arrangement, the noncollinear configuration is most stable making it the smallest cluster to feature a noncollinear ground state. The results are discussed in view of the recent experimental Stern-Gerlach profiles
The collision of two slowly rotating, initially non boosted, black holes in the close limit
We study the collision of two slowly rotating, initially non boosted, black
holes in the close limit. A ``punctures'' modification of the Bowen - York
method is used to construct conformally flat initial data appropriate to the
problem. We keep only the lowest nontrivial orders capable of giving rise to
radiation of both gravitational energy and angular momentum. We show that even
with these simplifications an extension to higher orders of the linear
Regge-Wheeler-Zerilli black hole perturbation theory, is required to deal with
the evolution equations of the leading contributing multipoles. This extension
is derived, together with appropriate extensions of the Regge-Wheeler and
Zerilli equations. The data is numerically evolved using these equations, to
obtain the asymptotic gravitational wave forms and amplitudes. Expressions for
the radiated gravitational energy and angular momentum are derived and used
together with the results of the numerical evolution to provide quantitative
expressions for the relative contribution of different terms, and their
significance is analyzed.Comment: revtex, 18 pages, 2 figures. Misprints corrected. To be published in
Phys. Rev.
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