Comment on The Evidence for a Pentaquark and Kinematic Reflections

The Regge exchange model used by Dzierba et al. is shown to be questionable, since the pion pole term is not allowed. Hence the Regge amplitudes in their calculation are exaggerated. The amount of kinematic reflection in the mass spectrum of the (nK+) system, which is one decay channel of a possible pentaquark, is not well justified in the fitting procedure used by Dzierba et al., as shown by comparison with the (K+K-) invariant mass spectrum, which is one decay channel of the a_2 and f_2 tensor mesons. While kinematic reflections are still a concern in some papers that have presented evidence for the pentaquark, better quantitative calculations are needed to demonstrate the significance of this effect.Comment: Comment submitted to Phys. Rev. D (no figures

Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects

The incoherent pion photoproduction reaction gd-->pi-pp is considered theoretically in a wide energy region Eth =< Eg =< 2700 MeV. The model applied contains the impulse approximation as well as the NN- and piN-FSI amplitudes. The aim of the paper is to study a reliable way for getting the information on elementary gn-->pi-p reaction cross section beyond the impulse approximation for gd-->pi-pp. For the elementary gN-->piN, NN-->NN, and piN-->piN amplitudes, the results of the GW DAC are used. There are no additional theoretical constraints. The calculated cross section dSigma/dOmega(gd->pi-pp) are compared with existing data. The procedure used to extract information on the differential cross section dSigma/dOmega(gn-->pi-p) on the neutron from the deuteron data using the FSI correction factor R is discussed. The calculations for R versus pi-p CM angle \theta_1 of the outgoing pion are performed at different photon-beam energies with kinematical cuts for "quasi-free" process gn-->pi-p. The results show a sizeable FSI effect R \neq 1 from S-wave part of pp-FSI at small angles close to \theta_1 ~ 0: this region narrows as the photon energy increases. At larger angles, the effect is small (|R-1|<<1) and agrees with estimations of FSI in the Glauber approach.Comment: 28 pages, 5 figures, 1 tabl

Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies

We studied the kink-antikink collision process for the "double sine-Gordon" (DSG) equation in 1+1 dimensions at different values of the potential parameter $R>0$. For small values of $R$ we discuss the problem of resonance frequencies. We give qualitative explanation of the frequency shift in comparison with the frequency of the discrete level in the potential well of isolated kink. We show that in this region of the parameter $R$ the effective long-range interaction between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps

Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region

Differential cross sections for the process gn-->pi-p have been extracted from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction effects, using a diagrammatic technique taking into account the NN and piN final-state interaction amplitudes. Results are compared to previous measurements of the inverse process, pi-p--> ng, and recent multipole analyses.Comment: 6 pages, 4 figures. v2: Further clarifications and minor changes. A new figure inserte