N_c and m_pi dependence of rho and sigma mesons from unitarized Chiral Perturbation Theory

We review our work on the rho and sigma resonances derived from the Inverse Amplitude Method. In particular, we study the leading 1/N_c behavior of the resonances masses and widths and their evolution with changing m_pi. The 1/N_c expansion gives a clear definition of quark-antiquark states, which is neatly satisfied by the rho but not by the sigma, showing that its dominant component is not quark-antiquark. The m_pi dependence of the resonance properties is relevant to connect with lattice studies. We show that our predictions compare well with some lattice results and we find that the rho-pi-pi coupling constant is m_pi independent, in contrast with the sigma-pi-pi coupling, that shows a strong m_pi dependence.Comment: To appear in the Proceedings of the Chiral10 Workshop, June 21-24 2010. Valencia, Spai

Polarization phenomena in the reaction NN to NNpi near threshold

First calculations for spin-dependent observables of the reactions $pp \to pp\pi^0$, $pp \to pn\pi^+$ and $pp \to d\pi^+$ near threshold are presented, employing the J\"ulich model for pion production. The influence of resonant (via the excitation of the $\Delta (1232)$) and non-resonant p-wave pion production mechanisms on these observables is examined. For the reactions $pp \to pn\pi^+$ and $pp \to d\pi^+$ nice agreement of our predictions with the presently available data on spin correlation coefficents is observed whereas for $pp \to pp\pi^0$ the description of the data is less satisfying.Comment: 10 pages, 4 figure

Isospin breaking in pion-deuteron scattering and the pion-nucleon scattering lengths

In recent years, high-accuracy data for pionic hydrogen and deuterium have become the primary source of information on the pion-nucleon scattering lengths. Matching the experimental precision requires, in particular, the study of isospin-breaking corrections both in pion-nucleon and pion-deuteron scattering. We review the mechanisms that lead to the cancellation of potentially enhanced virtual-photon corrections in the pion-deuteron system, and discuss the subtleties regarding the definition of the pion-nucleon scattering lengths in the presence of electromagnetic interactions by comparing to nucleon-nucleon scattering. Based on the pi^{+/-} p channels we find for the virtual-photon-subtracted scattering lengths in the isospin basis a^{1/2}=(170.5 +/- 2.0) x 10^{-3} mpi^{-1} and a^{3/2}=(-86.5 +/- 1.8) x 10^{-3} mpi^{-1}.Comment: 6 pages, 1 figure, Proceedings for the 7th International Workshop on Chiral Dynamics, Newport News, Virginia, USA, August 6-10, 201

A practical parametrization for line shapes of near-threshold states

Numerous quarkonium(like) states lying near $S$-wave thresholds are observed experimentally. We propose a self-consistent approach to these near-threshold states compatible with unitarity and analyticity. The underlying coupled-channel system includes a bare pole and an arbitrary number of elastic and inelastic channels treated fully nonperturbatively. The resulting analytical parametrization is ideally suited for a combined analysis of the data available in various channels that is exemplified by an excellent overall description of the data for the charged $Z_b(10610)$ and $Z_b(10650)$ states.Comment: LaTeX2e, 5 pages, 1 figure, typos corrected, version published in Phys. Rev. Let

Interactions of Charmed Mesons with Light Pseudoscalar Mesons from Lattice QCD and Implications on the Nature of the D_{s0}^*(2317)

We study the scattering of light pseudoscalar mesons ($\pi$, $K$) off charmed mesons ($D$, $D_s$) in full lattice QCD. The S-wave scattering lengths are calculated using L\"uscher's finite volume technique. We use a relativistic formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-3/2 $D\pi$, $D_s\pi$, $D_sK$, isospin-0 $D\bar{K}$ and isospin-1 $D\bar{K}$ channels on the lattice. For the chiral extrapolation, we use a chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. It turns out that our results support the interpretation of the $D_{s0}^*(2317)$ as a $DK$ molecule. At the same time, we also update a prediction for the isospin breaking hadronic decay width $\Gamma(D_{s0}^*(2317)\to D_s\pi)$ to $(133\pm22)$ keV.Comment: 22 pages, 5 figures; a typo in Table II corrected (for the coefficients of the NLO amplitudes

Spin observables and the determination of the parity of Θ+\Theta^+ in photoproduction reactions

Spin observables in the photoproduction of the $\Theta^+$ are explored for the purpose of determining the parity of the $\Theta^+$. Based on reflection symmetry in the scattering plane, we show that certain spin observables in the photoproduction of the $\Theta^+$ can be related directly to its parity. We also show that measurements of both the target nucleon asymmetry and the $\Theta^+$ polarization may be useful in determining the parity of $\Theta^+$ in a model-independent way. Furthermore, we show that no combination of spin observables involving only the polarization of the photon and/or nucleon in the initial state can determine the parity of $\Theta^+$ unambiguously.Comment: LaTeX, 11 pages, minor revisio