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Albaladejo, M., Oller, J. A., Oset, E., Rios, G., & Roca, L. (2012). Finite volume treatment of pi pi scattering and limits to phase shifts extraction from lattice QCD. J. High Energy Phys., 08(8), 071–22pp.
Abstract: We study theoretically the effects of finite volume for pi pi scattering in order to extract physical observables for infinite volume from lattice QCD. We compare three different approaches for pi pi scattering (lowest order Bethe-Salpeter approach, N/D and inverse amplitude methods) with the aim of studying the effects of the finite size of the box in the potential of the different theories, specially the left-hand cut contribution through loops in the crossed t, u-channels. We quantify the error made by neglecting these effects in usual extractions of physical observables from lattice ()CD spectrum. We conclude that for pi pi phase-shifts in the scalar-isoscalar channel up to 800 MeV this effect is negligible for box sizes bigger than 2,5m(pi)(-1) and of the order of 5% at around 1.5 – 2m(pi)(-1). For isospin 2 the finite size effects can reach up to 10% for that energy. We also quantify the error made when using the standard Luscher method to extract physical observables from lattice QCD, which is widely used in the literature but is an approximation of the one used in the present work.
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Aceti, F., Molina, R., & Oset, E. (2012). X(3872) -> J/psi gamma decay in the D(D)over-bar* molecular picture. Phys. Rev. D, 86(11), 113007–13pp.
Abstract: From a picture of the X(3872) where the resonance is a bound state of D (D) over bar*- c.c., we evaluate the decay width into the J/psi gamma channel, which is sensitive to the internal structure of this state. For this purpose we evaluate the loops through which the X(3872) decays into its components, and the J/psi and the photon are radiated from these components. We use the local hidden gauge approach extrapolated to SU(4) with a particular SU(4) breaking. The radiative decay involves anomalous couplings, and we obtain acceptable values which are compared to experiments and results of other calculations. Simultaneously, we evaluate the decay rate for the X(3872) into J/psi omega and J/psi rho, and the results obtained for the ratio of these decay widths are compatible with the experiment. We also show that considering only the (D) over bar D-0*(0) – c.c. component in the radiative decay reduces the partial decay width in more than three orders of magnitude, in large discrepancy with experiment.
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Oset, E. (2013). On the ambiguities of sign determination of the S-matrix from energy levels in a finite box. Eur. Phys. J. A, 49(3), 32–4pp.
Abstract: In a recent paper the authors make a study on the determination of the S-matrix elements for scattering of particles in the infinite volume from the energy levels in a finite box for the case of multiple channels. The study is done with a toy model in 1+1 dimension and the authors find that there is some ambiguity in the sign of nondiagonal matrix elements, casting doubts on whether the needed observables in the infinite volume can be obtained from the energy levels of the box. In this paper I present an easy derivation, confirming the ambiguity of the sign and argue that this, however, does not put restrictions in the determination of observables.
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Roca, L., & Oset, E. (2013). Lambda(1405) poles obtained from pi(0)Sigma(0) photoproduction data. Phys. Rev. C, 87(5), 055201–8pp.
Abstract: We present a strategy to extract the position of the two Lambda(1405) poles from experimental photoproduction data measured recently at different energies in the gamma p -> K+pi(0)Sigma(0) reaction at Jefferson Laboratory. By means of a chiral dynamics motivated potential with free parameters, we solve the Bethe-Salpeter equation in the coupled channels (K) over barN and pi Sigma in isospin I = 0 and parametrize the amplitude for the photonuclear reaction in terms of a linear combination of the pi Sigma -> pi Sigma and (K) over barN -> pi Sigma scattering amplitudes in I = 0, with a different linear combination for each energy. Good fits to the data are obtained with some sets of parameters, by means of which one can also predict the cross section for the K- p -> pi(0)Sigma(0) reaction. These later results help us decide among the possible solutions. The result is that the different solutions lead to two poles similar to those found in the chiral unitary approach. With the best result we find the two Lambda(1405) poles at 1385 – 68i MeV and 1419 – 22i MeV.
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Xiao, C. W., & Oset, E. (2013). Three methods to detect the predicted D(D)over-bar scalar meson X(3700). Eur. Phys. J. A, 49(4), 52–6pp.
Abstract: In analogy to the f(0)(500), which appears as a pi pi resonance in chiral unitary theory, and the f(0)(980), which appears as a quasibound K (K) over bar state, the extension of this approach to the charm sector also predicts a quasibound D (D) over bar state with mass around 3720 MeV, named as X(3700), for which some experimental support is seen in the e(+)e(-) -> J/psi D (D) over bar reaction close to the D (D) over bar threshold. In the present work we propose three different experiments to observe it as a clear peak. The first one is the radiative decay of the psi(3770), psi(3770) -> gamma X(3700) -> gamma eta eta'. The second one proposes the analogous reaction psi(4040) -> gamma X(3700) -> gamma eta eta' and the third reaction is the e(+)e(-) -> J/psi X(3700) -> J/psi eta eta'. Neat peaks are predicted for all the reactions and the calculated rates are found within measurable range in present facilities.
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