Study of the threshold behavior of the η\etaN scattering amplitude through the associated photoproduction of ϕ\phi- and η\eta-mesons

We suggest that the $\gamma p \to \phi \eta p$ reaction cross section, in the kinematics where the $\eta p$ invariant mass in the final state lies between the threshold value (m$_p$+m$_\eta$) and the N*(1535) resonance mass, is largely determined by the $\eta N$ scattering amplitude close to threshold. The initial photon energy is chosen in the range $4 < E_\gamma^{Lab} < 5$ GeV, in order to reach low (absolute) values of the squared 4-momentum transfer from the initial photon to the final $\phi$-meson. In these conditions, we expect the t-channel $\pi^0$- and $\eta$-meson exchanges to drive the dynamics underlying the $\gamma p \to \phi \eta p$ process. We show that the $\eta$-exchange is the dominating contribution to the cross section while the $\pi^0$-exchange is negligible. The $\eta$-$\pi^0$ interference is of the order of $20 - 30$. The sign of this term is not known and alters significantly our results. Data on the $\gamma p \to \phi \eta p$ process would be therefore very useful to help unravelling the behavior of the $\eta p$ scattering amplitude close to threshold and assessing the possibility of producing $\eta$-nucleus bound states.Comment: 8 pages, 6 figures, Invited talk at MESON 2006, June 9th-13th, 2006, Cracow (Poland

e+e- pair production from nucleon targets in the resonance region

We present consistent theoretical descriptions of the $\pi N \to e^+e^- N$ and $\gamma N \to e^+e^- N$ reactions on proton and neutron targets for total center of mass energies $\sqrt s$ ranging between 1.50 GeV and 1.75 GeV. These reactions are complementary to study the coupling of low-lying baryon resonances to vector meson-nucleon channels. We show in particular how the resonant structure of the amplitudes for both processes generates specific and large quantum interferences between $\rho$- and $\omega$-meson decays into $e^+e^-$ pairs. Data on the $\pi N \to e^+e^- N$ and $\gamma N \to e^+e^- N$ reactions are expected in the near future from the HADES program at GSI and from dilepton studies with CLAS at JLab.Comment: 6 pages, 6 figures, Paper presented at Hirschegg 2004, 'Probing nuclei and nucleons with electrons and photons', January 12th-16th, 200

On kinematical constraints in the hadrogenesis conjecture for the baryon resonance spectrum

We consider the reaction dynamics of bosons with negative parity and spin $0$ or $1$ and fermions with positive parity and spin $\frac{1}{2}$ or $\frac{3}{2}$. Such systems are of central importance for the computation of the baryon resonance spectrum in the hadrogenesis conjecture. Based on a chiral Lagrangian the coupled-channel partial-wave scattering amplitudes have to be computed. We study the generic properties of such amplitudes. A decomposition of the various scattering amplitudes into suitable sets of invariant functions expected to satisfy Mandelstam's dispersion-integral representation is presented. Sets are identified that are free from kinematical constraints and that can be computed efficiently in terms of a novel projection algebra. From such a representation one can deduce the analytic structure of the partial-wave amplitudes. The helicity and the conventional angular-momentum partial-wave amplitudes are kinematically constrained at the Kibble conditions. Therefore an application of a dispersion-integral representation is prohibitively cumbersome. We derive covariant partial-wave amplitudes that are free from kinematical constraints at the Kibble conditions. They correspond to specific polynomials in the 4-momenta and Dirac matrices that solve the various Bethe-Salpeter equations in the presence of short-range interactions analytically.Comment: 18 page

Dynamics of strong and radiative decays of Ds mesons

The positive parity scalar D$_{s0}^*$(2317) and axial-vector D$_{s1}^*$(2460) charmed strange mesons are generated by coupled-channel dynamics through the s-wave scattering of Goldstone bosons off the pseudoscalar and vector D(D$_s$)-meson ground states. The attraction leading to the specific masses of these states reflects the chiral symmetry breaking scale which characterizes the Weinberg-Tomozawa interaction in the chiral Lagrangian. Chiral corrections to order Q$_\chi^2$ are calculated and found to be small. The D$_{s0}^*$(2317) and D$_{s1}^*$(2460) mesons decay either strongly into the isospin-violating $\pi^0$D$_s$ and $\pi^0$D$_s^*$ channels or electromagnetically. We show that the $\pi^0$-$\eta$ and (K$^0$D$^+$-K$^+$D$^0$) mixings act constructively to generate strong widths of the order of 140 keV. The one-loop contribution to the radiative decay amplitudes of scalar and axial-vector states is calculated using the electromagnetic Lagrangian to chiral order Q$_\chi^2$. We show the importance of taking into account processes involving light vector mesons explicitly in the dynamics of electromagnetic decays to obtain a satisfactory description of the available data.Comment: Contribution to the Meson 2008 Conference, June 6-10, Cracow, Polan

The πN→e+e−N\pi N \to e^+e^- N reaction close to the vector meson production threshold

The $\pi^-p \to e^+e^- n$ and $\pi^+n \to e^+e^- p$ reaction cross sections are calculated below and in the vicinity of the vector meson ($\rho^0$, $\omega$) production threshold. These processes are largely responsible for the emission of $e^+e^-$ pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector meson-nucleon channels. The vector mesons materialize subsequently into $e^+e^-$ pairs. Using $\pi N\to \rho^0 N$ and $\pi N \to \omega N$ amplitudes calculated in the center of mass energy interval $1.4<\sqrt s <1.8$ GeV, we compute the $\pi^-p \to e^+e^- n$ and $\pi^+n \to e^+e^- p$ reaction cross sections in these kinematics. Below the vector meson production threshold, the $\rho^0 - \omega$ interference in the $e^+e^-$ channel appears largely destructive for the $\pi^-p \to e^+e^- n$ cross section and constructive for the $\pi^+n \to e^+e^- p$ cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector meson-nucleon channels to low-lying baryon resonances.Comment: Talk given at the Budapest'02 Workshop on Quark and Hadron Dynamics, Budapest (Hungary), March 3rd-7th, 200

Who Prices Locally? Survey Evidence of Swiss Exporters

Survey information on Swiss exporters is used to test the hypothesis that firm-specific factors, in particular firm size, are important determinants of pricing--to-market (PTM). The survey asked exporters whether they set different prices across markets and, if so, whether price segmentation occurred because of pricing conditions in the local market or other factors. The empirical analysis is based on a probit model that regresses a binary-choice variable of PTM on firm size and other control variables. The main empirical finding is that firm size and PTM are positively and significantly correlated. A further result is that while firms whose main export market is in the Euro area are less likely to engage in PTM, firm size plays a bigger role for them. These results are robust across different PTM classifications, regression specifications, export destinations, and industrial sectors.Pricing to markets, local currency pricing, firm size

Who Prices Locally? Survey Evidence of Swiss Exporters

Survey information on Swiss exporters is used to test the hypothesis that firm-specific factors, in particular firm size, are important determinants of pricing-to-market (PTM). The survey asked exporters whether they set dif- ferent prices across markets and, if so, whether price segmentation occurred because of pricing conditions in the local market or other factors. The empirical analysis is based on a probit model that regresses a binary-choice variable of PTM on firm size and other control variables. The main empirical finding is that firm size and PTM are positively and significantly correlated. A further result is that while firms whose main export market is in the Euro area are less likely to engage in PTM, firm size plays a bigger role for them. These results are robust across different PTM classifications, regression specifications, export destinations, and industrial sectors.Pricing to markets, local currency pricing, .rm size