2,156 research outputs found
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
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
Isospin-breaking two-nucleon force with explicit Delta-excitations
We study the leading isospin-breaking contributions to the two-nucleon
two-pion exchange potential due to explicit Delta degrees of freedom in chiral
effective field theory. In particular, we find important contributions due to
the delta mass splittings to the charge symmetry breaking potential that act
opposite to the effects induced by the nucleon mass splitting.Comment: 10 pages, 4 figure
Što znamo o kršenju invarijantnosti obrata vremena
The time reversal (TR) transformation and its consequences are reviewed. Recent experiments and theories are discussed and limits on time reversal invariance (TRI)- breaking are given. Finally, future experiments are cited. We discuss TRI independently of the CP symmetry.Razmatra se pretvorba vremenskog obrata (TR) i njene posljedice. Raspravljaju se nedavna mjerenja i teorije i daju granice kršenja invarijantnosti obrata vremena (TRI). Na kraju, navode se buduća mjerenja. TRI se raspravlja neovisno o CP simetriji
Spin of ground state baryons
We calculate the quark spin contribution to the total angular momentum of
flavor octet and flavor decuplet ground state baryons using a spin-flavor
symmetry based parametrization method of quantum chromodynamics. We find that
third order SU(6) symmetry breaking three-quark operators are necessary to
explain the experimental result Sigma_1=0.32(10). For spin 3/2 decuplet baryons
we predict that the quark spin contribution is Sigma_3=3.93(22), i.e.
considerably larger than their total angular momentum.Comment: 8 page
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