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

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