Study of the strong Σb→Λb π\Sigma_b\to \Lambda_b\, \pi and Σb∗→Λb π\Sigma_b^{*}\to \Lambda_b\, \pi in a non-relativistic quark model

We present results for the strong widths corresponding to the $\Sigma_b\to \Lambda_b\, \pi$ and $\Sigma_b^{*}\to \Lambda_b\, \pi$ decays. We apply our model in Ref. Phys. Rev. D 72, 094022 (2005) where we previously studied the corresponding transitions in the charmed sector. Our non-relativistic constituent quark model uses wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the axial current matrix elements.Comment: 6 latex pages, 1 table, new references adde

Meson Resonances at large Nc: Complex Poles vs Breit-Wigner Masses

The rigorous quantum mechanical definition of a resonance requires determining the pole position in the second Riemann sheet of the analytically continued partial wave scattering amplitude in the complex Mandelstam s-variable plane. For meson resonances we investigate the alternative Breit-Wigner (BW) definition within the large Nc expansion. By assuming that the pole position is ${\cal O} (N_C^{0})$ and exploiting unitarity, we show that the BW determination of the resonance mass differs from the pole position by ${\cal O} (N_C^{-2})$ terms, which can be extracted from pi-pi scattering data. For the case of the f0(600) pole, the BW scalar mass is predicted to occur at about 700 MeV while the true value is located at about 800 MeV.Comment: 7 pages. No figures. (elsevier preprint

Coherent pion production off nuclei at T2K and MiniBooNE energies revisited

As a result of a new improved fit to old bubble chamber data of the dominant axial C_5^A nucleon-to-Delta form factor, and due to the relevance of this form factor for neutrino induced coherent pion production, we re-evaluate our model predictions in Phys. Rev. D79, 013002 (2009) for different observables of the latter reaction. Central values for the total cross sections increase by 20% to 30%, while differential cross sections do not change their shape appreciably. Furthermore, we also compute the uncertainties on total, differential and flux averaged cross sections induced by the errors in the determination of C_5^A. Our new results turn out to be compatible within about 1 sigma with the former ones. Finally, we stress the existing tension between the recent experimental determination of the sigma(CC coh \pi^+)/sigma(NC coh \pi^0) ratio by the SciBooNE Collaboration and the theoretical predictions.Comment: 6 latex pages, 1 table, 2 figures. Shortened versio

Hyperfine mixing in b→cb\to c semileptonic decay of doubly heavy baryons

We qualitatively corroborate the results of W. Roberts and M. Pervin in Int. J. Mod. Phys. A 24, 2401 (2009) according to which hyperfine mixing greatly affects the decay widths of $b\to c$ semileptonic decays involving doubly heavy $bc$ baryons. However, our predictions for the decay widths of the unmixed states differ from those reported in the work of Roberts and Pervin by a factor of 2, and this discrepancy translates to the mixed case. We further show that the predictions of heavy quark spin symmetry, might be used in the future to experimentally extract information on the admixtures in the actual physical $bc$ baryons, in a model independent manner.Comment: 7 Latex pages, 4 Table

Thermal Field Theory in a wire: Applications of Thermal Field Theory methods to the propagation of photons in a one-dimensional plasma

We apply the Thermal Field Theory (TFT) methods to study the propagation of photons in a plasma wire, that is, a system in which the electrons are confined to a one-dimensional tube or wire, but are otherwise free. We find the appropriate expression for the photon \emph{free-field} propagator in such a medium, and write down the dispersion relation in terms of the free-field propagator and the photon self-energy. The self-energy is then calculated in the one-loop approximation and the corresponding dispersion relation is determined and studied in some detail. Our work differs from previous work on this subject in that we do not adopt any specific electronic wave functions in the coordinates that are transverse to the idealized wire, or rely on particular features of the electronic structure. We treat the electrons as a free gas of particles, constrained to move in one dimension, but otherwise in a model-independent way only following the rules of TFT adapted to the situation at hand. For the appropriate conditions of the plasma the \emph{static approximation} can be employed and the dispersion relation reduces to the results obtained in previous works, but the formula that we obtain is valid under more general conditions, including those in which the static approximation is not valid. In particular, the dispersion relation has several branches, which are not revealed if the static approximation is used. The dispersion relations obtained reproduce several unique features of these systems that have been observed in recent experiments.Comment: 17 pages Revised and extended discussion of the dispersion relation

Couplings in coupled channels versus wave functions: application to the X(3872) resonance

We perform an analytical study of the scattering matrix and bound states in problems with many physical coupled channels. We establish the relationship of the couplings of the states to the different channels, obtained from the residues of the scattering matrix at the poles, with the wave functions for the different channels. The couplings basically reflect the value of the wave functions around the origin in coordinate space. In the concrete case of the X(3872) resonance, understood as a bound state of \ddn and \ddc (and $c.c.$), with the \ddn loosely bound, we find that the couplings to the two channels are essentially equal leading to a state of good isospin I=0 character. This is in spite of having a probability for finding the \ddn state much larger than for \ddc since the loosely bound channel extends further in space. The analytical results, obtained with exact solutions of the Schr\"odinger equation for the wave functions, can be useful in general to interpret results found numerically in the study of problems with unitary coupled channels methods.Comment: 14 pages, 4 figure

Isospin breaking effects in the dynamical generation of the X(3872)

We have studied isospin breaking effects in the X(3872) resonance and found a natural explanation for the branching fraction of the X decaying to $J/\psi$ with two and three pions being close to unit. Within our framework the X(3872) is a dynamically generated resonance in coupled channels. We also study the relationship between the couplings of the resonance to the coupled channels with its wave function, which further helps us to understand the isospin structure of the resonance.Comment: 5 pages, 1 figure. To appear in the Proceedings of XIII International Conference on Hadron Spectroscopy, November 29 - December 4, 2009, Florida State Universit

Single photon production induced by (anti)neutrino neutral current scattering on nucleons and nuclear targets

We review our theoretical approach to neutral current photon emission on nucleons and nuclei in the few-GeV energy region, relevant for neutrino oscillation experiments. These reactions are dominated by the weak excitation of the $\Delta(1232)$ resonance but there are also important non-resonant contributions. We have also included terms mediated by nucleon excitations from the second resonance region. On nuclei, Pauli blocking, Fermi motion and the in-medium $\Delta$ resonance broadening have been taken into account for both incoherent and coherent reaction channels. With this model, the number and distributions of photon events at the MiniBooNE and T2K experiments have been obtained. We have also compared to the NOMAD upper limit at higher energies. The implications of our findings and future perspectives are discussed.Comment: 10 pages, 7 figures, Proceedings of the CETUP* 2014 Workshop on Neutrino Interaction

Wave functions for dynamically generated resonances; the two Λ(1405)\Lambda(1405) and Λ(1670)\Lambda(1670)

In this work we develop a formalism to evaluate wave functions in momentum and coordinate space for the resonant states dynamically generated in a unitary coupled channel approach. The on shell approach for the scattering matrix, commonly used, is also obtained in Quantum Mechanics with a separable potential, which allows one to write wave functions in a trivial way. We develop useful relationships among the couplings of the dynamically generated resonances to the different channels and the wave functions at the origin. The formalism provides an intuitive picture of the resonances in the coupled channel approach, as bound states of one bound channel, which decays into open ones. It also provides an insight and practical rules for evaluating couplings of the resonances to external sources and how to deal with final state interaction in production processes. As an application of the formalism we evaluate the wave functions of the two $\Lambda(1405)$ states in the $\pi \Sigma$, $\bar{K} N$ and other coupled channels. It also offers a practical way to study three body systems when two of them cluster into a resonance.Comment: 5pages, 1 figure. To appear in the proceedings of the International Workshop on Chiral Symmetry in Hadrons and Nuclei (Chiral10), Valencia, Spain, Jun 21-24, 201