Chiral dynamics in the gamma p --> pi^0 eta p and gamma p --> pi^0 K^0 Sigma^+ reactions

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ resonance is dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and a baryon belonging to the $\Delta(1232)$ decuplet. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $3/2^-$ states. The first reaction is shown to lead to sizable cross sections and the $N^*(1535)$ resonance shape is seen clearly in the $\eta p$ invariant mass distribution. The same dynamical model is shown to lead to much smaller cross sections at low energies in the second reaction. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.Comment: 22 pages, 22 figure

Chiral Dynamics and S-wave Contributions in Semileptonic B decays

The flavor-changing neutral current process $b\to s l^+l^-$ is beneficial to testing the standard model and hunting for new physics scenarios. In exclusive decay modes like $B\to K^*(892)l^+l^-$, the S-wave effects may not be negligible and thus have to be reliably estimated. Using the scalar form factors derived from dispersion relations in two channels and matched to Chiral Perturbation Theory, we investigate the S-wave contributions in $\bar B^0\to K^- \pi^+ l^+l^-$, with the $K\pi$ invariant mass lying in the vicinity of the mass of $K^*(892)$, and the $B_s\to K^- K^+ l^+l^-$ with $m_{KK}\sim m_{\phi}$. We find that the S-wave will modify differential decay widths by about 10% in the process of $\bar B^0\to K^- \pi^+ l^+l^-$ and about 5% in $B_s\to K^- K^+ l^+l^-$. A forward-backward asymmetry for the charged kaon in the final state arises from the interference between the S-wave and P-wave contributions. The measurement of this asymmetry offers a new way to determine the variation of the $K\pi$ S-wave phase versus the invariant mass.Comment: 26 pages, 10 figure

Radiative decay of the Delta(1700)

Electromagnetic properties provide information about the structure of strongly interacting systems and allow for independent tests of hadronic models. The radiative decay of the Delta(1700) is studied, which appears dynamically generated in a coupled channel approach from the rescattering of the (3/2^+) decuplet of baryons with the (0^-) octet of pseudoscalar mesons. The radiative decay is predicted from the well-known couplings of the photon to the mesons and hadrons which constitute this resonance in the dynamical picture.Comment: 14 pages, 4 figure

Heavy quark free energies and screening at finite temperature and density

We study the free energies of heavy quarks calculated from Polyakov loop correlation functions in full 2-flavour QCD using the p4-improved staggered fermion action. A small but finite Baryon number density is included via Taylor expansion of the fermion determinant in the Baryo-chemical potential mu. For temperatures above Tc we extract Debye screening masses from the large distance behaviour of the free energies and compare their mu-dependence to perturbative results.Comment: 6 pages, Presented at 23rd International Symposium on Lattice Field Theory (Lattice 2005), Trinity College, Dublin, Ireland, 25-30 Jul 200

The phase and pole structure of the N*(1535) in piN-->piN and gammaN-->piN

The nature of some baryonic resonances is still an unresolved issue. The case of the N*(1535) is particularly interesting in this respect due to the nearby etaN threshold and interference with the N*(1650). The N*(1535) has been described as a threshold effect, as a genuine 3-quark resonance, or as dynamically generated from the interaction of the octet of baryons with the octet of mesons. In the scheme of dynamical generation, predictions for the interaction of the N*(1535) with the photon can be made. In this study, we simultaneously analyze the role of the N*(1535) in the piN-->piN and gammaN-->piN reactions and compare to the respective amplitudes from partial wave analyses. This test is very sensitive to the meson-baryon components of the N*(1535).Comment: 22 pages, 16 figures; updated to revised version accepted by EPJ

S- and p-wave structure of S=−1S=-1 meson-baryon scattering in the resonance region

We perform a simultaneous analysis of s- and p-waves of the $S=-1$ meson-baryon scattering amplitude using all low-energy experimental data. For the first time, differential cross section data are included for chiral unitary coupled-channel models. From this model s- and p-wave amplitudes are extracted and we observe both well-known $I(J^P)=0(1/2^-)$ s-wave states as well as a new $I(J^P)=1(1/2^+)$ state absent in quark models and lattice QCD results. Multiple statistical and phenomenological tests suggest that, while the data clearly require an $I=1$ p-wave resonance, the new state just accounts for the absence of the decuplet $\Sigma(1385)3/2^+$ in the model.Comment: 8 pages, 7 figure