12,905 research outputs found
Photoproduction with Nucleon Resonances
We investigate the reaction mechanism of photoproduction off
the neutron target, i.e., , in the range of GeV. We employ an effective Lagrangian method at the tree-level Born
approximation combining with a Regge approach. As a background, the
-Reggeon trajectory is taken into account in the channel and
and hyperons in the -channel Feynman diagram. In addition, the role
of various nucleon resonances listed in the Particle Data Group (PDG) is
carefully scrutinized in the channel where the resonance parameters are
extracted from the experimental data and constituent quark model. We present
our numerical results of the total and differential cross sections and compare
them with the recent CLAS data. The effect of the narrow nucleon resonance
on cross sections is studied in detail and it turns out that
its existence is essential in photoproduction to reproduce the
CLAS data.Comment: 4 pages, 3 figures, Proceedings of "8th International Conference on
Quarks and Nuclear Physics (QNP2018)", November 13-17, 2018, Tsukuba, Japa
Polygonal words in free groups
A longstanding question of Gromov asks whether every one-ended
word-hyperbolic group contains a subgroup isomorphic to the fundamental group
of a closed hyperbolic surface. An infinite family of word-hyperbolic groups
can be obtained by taking doubles of free groups amalgamated along words that
are not proper powers. We define a set of polygonal words in a free group of
finite rank, and prove that polygonality of the amalgamating word guarantees
that the associated square complex virtually contains a -injective
closed surface. We provide many concrete examples of classes of polygonal
words. For instance, in the case when the rank is 2, we establish polygonality
of words without an isolated generator, and also of almost all simple height 1
words, including Baumslag--Solitar relator for .Comment: 23 pages, 8 figure
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