On the existence of exotic and non-exotic multiquark meson states

To obtain an exact solution of a four-body system containing two quarks and two antiquarks interacting through two-body terms is a cumbersome task that has been tackled with more or less success during the last decades. We present an exact method for the study of four-quark systems based on the hyperspherical harmonics formalism that allows us to solve it without resorting to further approximations, like for instance the existence of diquark components. We apply it to systems containing two heavy and two light quarks using different quark-quark potentials. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models.Comment: 3 pages. Contribution to the 20th European Conference on Few-Body Problems in Physics, Pisa, Italy. To be published in Few-Body system

An explanation of the Δ5/2−(1930)\Delta_{5/2^{-}}(1930) as a ρΔ\rho\Delta bound state

We use the $\rho\Delta$ interaction in the hidden gauge formalism to dynamically generate $N^{\ast}$ and $\Delta^{\ast}$ resonances. We show, through a comparison of the results from this analysis and from a quark model study with data, that the $\Delta_{5/2^{-}}(1930),$ $\Delta_{3/2^{-}}(1940)$ and $\Delta_{1/2^{-}}(1900)$ resonances can be assigned to $\rho\Delta$ bound states. More precisely the $\Delta_{5/2^{-}}(1930)$ can be interpreted as a $\rho\Delta$ bound state whereas the $\Delta_{3/2^{-}}(1940)$ and $\Delta_{1/2^{-}}(1900)$ may contain an important $\rho\Delta$ component. This interpretation allows for a solution of a long-standing puzzle concerning the description of these resonances in constituent quark models. In addition we also obtain degenerate $J^{P}=1/2^{-},3/2^{-},5/2^{-}$ $N^{*}$ states but their assignment to experimental resonances is more uncertain.Comment: 19 pags, 8 fig

Are there compact heavy four-quark bound states?

We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical modelsComment: 10 pages, 1 figure. Accepted for publication in Phys. Rev.

Open-charm meson spectroscopy

We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold, being broad resonances. We study the electromagnetic decay widths as basic tools to scrutiny their nature. The proposed explanation incorporates in a natural way the most recently discovered mesons in charmonium spectroscopy.Comment: 15 pages, 5 tables. Accepted for publication in Phys. Rev.

Four-quark spectroscopy within the hyperspherical formalism

We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ and $1^{+-}$ states become attractive only for larger mass of the quarks.Comment: 20 pages, 3 figure

Charm meson resonances in D→PℓνD \to P \ell \nu decays

Motivated by recent experimental results we reconsider semileptonic $D \to P \ell \nu_{\ell}$ decays within a model which combines heavy quark symmetry and properties of the chiral Lagrangian. We include excited charm meson states, some of them recently observed, in our Lagrangian and determine their impact on the charm meson semileptonic form factors. We find that the inclusion of excited charm meson states in the model leads to a rather good agreement with the experimental results on the $q^2$ shape of the $F_+(q^2)$ form factor. We also calculate branching ratios for all $D \to P \ell \nu_{\ell}$ decays.Comment: 9 pages, 4 figures; minor corrections, added some discussion, version as publishe

Nature of the light scalar mesons

Despite the apparent simplicity of meson spectroscopy, light scalar mesons cannot be accommodated in the usual $q\bar q$ structure. We study the description of the scalar mesons below 2 GeV in terms of the mixing of a chiral nonet of tetraquarks with conventional $q\bar q$ states. A strong diquark-antidiquark component is found for several states. The consideration of a glueball as dictated by quenched lattice QCD drives a coherent picture of the isoscalar mesons.Comment: 14 pages, 1 figure, accepted for publication in Phys. Rev.

A topological charge selection rule for phase singularities

We present an study of the dynamics and decay pattern of phase singularities due to the action of a system with a discrete rotational symmetry of finite order. A topological charge conservation rule is identified. The role played by the underlying symmetry is emphasized. An effective model describing the short range dynamics of the vortex clusters has been designed. A method to engineer any desired configuration of clusters of phase singularities is proposed. Its flexibility to create and control clusters of vortices is discussed.Comment: 4 pages, 3 figure