Notes on exotic anti-decuplet of baryons

We emphasize the importance of identifying non-exotic SU(3) partners of the Theta^+ pentaquark, and indicate possible ways how to do it. We also use the soliton picture of baryons to relate Reggeon couplings of various baryons. These relations are used to estimate the Theta^+ production cross section in high energy processes. We show that the corresponding cross sections are significantly suppressed relative to the production cross sections of usual baryons. Finally, we present spin non-flip form factors of the anti-decuplet baryons in the framework of the chiral quark soliton model.Comment: Contribution to the Workshop On The Physics Of Excited Nucleons (NSTAR 2004) 24-27 Mar 2004, Grenoble, Franc

Mixing and decays of the antidecuplet in the context of approximate SU(3) symmetry

We consider mixing of the antidecuplet with three J^P=1/2^+ octets (the ground-state octet, the octet containing N(1440), \Lambda(1600), \Sigma(1660) and \Xi(1690) and the octet containing N(1710), \Lambda(1800), \Sigma(1880) and \Xi(1950)) in the framework of approximate flavor SU(3) symmetry. We give general expressions for the partial decay widths of all members of the antidecuplet as functions of the two mixing angles. Identifying N_{anti-10} with the N(1670) observed by the GRAAL experiment, we show that the considered mixing scenario can accommodate all present experimental and phenomenological information on the \Theta^+ and N_{anti-10} decays: \Theta^+ could be as narrow as 1 MeV; the N_{anti-10} -> N + \eta decay is sizable, while the N_{anti-10} ->N + \pi decay is suppressed and the N_{anti-10} ->\Lambda + K decay is possibly suppressed. Constraining the mixing angles by the N_{anti-10} decays, we make definite predictions for the \Sigma_{anti-10} decays. We point out that \Sigma_{anti-10} with mass near 1770 MeV could be searched for in the available data on K_S p invariant mass spectrum, which already revealed the \Theta^+ peak. It is important to experimentally verify the decay properties of \Sigma(1770) because its mass and J^P=1/2^+ make it an attractive candidate for \Sigma_{anti-10}.Comment: 57 pages, 31 figures, 4 table

A note on inequalities for the masses of the lightest pi-pi resonances in large N_c QCD

We derive and analyse inequalities relating masses of the lightest pi-pi resonances (rho and sigma) to low energy couplings of the effective chiral Lagrangian in the limit of large number of colours.Comment: 8 pages, discussion of the hybrid component is correcte

One Loop Chiral Corrections to Hard Exclusive Processes:I. Pion Case

We computed the leading non-analytic chiral corrections to the generalized parton distributions (GPDs) of the pion and to the two-pion distribution amplitudes. This allows us to obtain the corresponding corrections for the hard exclusive processes, such as gamma^* gamma -> pi pi, gamma^* N -> 2pi N' and deeply virtual Compton scattering on the pion target.Comment: 17 pages, 3 figure

Two-pion light-cone distribution amplitudes from the instanton vacuum

We calculate the two-pion light-cone distribution amplitudes in the effective low-energy theory based on the instanton vacuum. These generalized distribution amplitudes describe the soft (non-perturbative) part of the process $\gamma^*\gamma \to \pi\pi$ in the region where the c.m. energy is much smaller than the photon virtuality. They can also be used in the analysis of exclusive processes such as $\gamma^* p \to p + 2\pi, 3\pi$ etc.Comment: 13 pages, LaTeX, 4 figures included using eps