Predicting D -> sigma pi

We examine the D -> sigma pi amplitude through a constituent quark-meson model, incorporating heavy quark and chiral symmetries, finding a good agreement with the recent E791 data analysis of D -> 3 pi via sigma.Comment: 6 pages, RevTex, One new contribution added, typos correcte

Exotic Hadrons with Hidden Charm and Strangeness

We investigate on exotic tetraquark hadrons of the kind [cs][cbar sbar] by computing their spectrum and decay modes within a constituent diquark-antidiquark model. We also compare these predictions with the present experimental knowledge.Comment: 6 pages, 2 figures, minor changes made, references adde

A Comment on "A note on polarized light from Magnetars: QED effects and axion-like particles" by L.M. Capparelli, L. Maiani and A.D. Polosa

The recent detection of a large polarization degree in the optical emission of an isolated neutron star led to the suggestion that this has been the first evidence of vacuum polarization in a strong magnetic field, an effect predicted by quantum electrodynamics but never observed before. This claim was challanged in a paper by Capparelli, Maiani & Polosa (2017), according to whom a much higher polarization degree would be necessary to positively identify vacuum polarization. Here we show that their conclusions are biased by several inadequate assumptions and have no impact on the original claim.Comment: 10 pages, 2 figure

XYZ: four-quark states?

The observation of many unexpected states decaying into heavy quarkonia has challenged the usual Q-Qbar interpretation. We will discuss the nature of some of the charmonium-like resonances recently observed by BES III and LHCb, and their identication according to the compact tetraquark model. We also commment the production of light nuclei in hadron collisions and the relevance for the physics of the X(3872).Comment: 5 pages, 2 figures, 1 table. Contribution to the proceedings of "IFAE 2015 Incontri di Fisica delle Alte Energie", Roma 8-10 April 201

Hamiltonian, Path Integral and BRST Formulations of Large N Scalar QCD2QCD_{2} on the Light-Front and Spontaneous Symmetry Breaking

Recently Grinstein, Jora, and Polosa have studied a theory of large-$N$ scalar quantum chromodynamics in one-space one-time dimension. This theory admits a Bethe-Salpeter equation describing the discrete spectrum of quark-antiquark bound states. They consider gauge fields in the adjoint representation of $SU(N)$ and scalar fields in the fundamental representation. The theory is asymptotically free and linearly confining. The theory could possibly provide a good field theoretic framework for the description of a large class of diquark-antidiquark (tetra-quark) states. Recently we have studied the light-front quantization of this theory without a Higgs potential. In the present work, we study the light-front Hamiltonian, path integral and BRST formulations of the theory in the presence of a Higgs potential. The light-front theory is seen to be gauge-invariant, possessing a set of first-class constraints. The explicit occurrence of spontaneous symmetry breaking in the theory is shown in unitary gauge as well as in the light-front 't Hooft gauge.Comment: Accepted for publication in Eur. Phys. J.

Hybridized tetraquarks

We propose a new interpretation of the neutral and charged X,Z exotic hadron resonances. Hybridized-tetraquarks are neither purely compact tetraquark states nor bound or loosely bound molecules but rather a manifestation of the interplay between the two. While meson molecules need a negative or zero binding energy, its counterpart for h -tetraquarks is required to be positive. The formation mechanism of this new class of hadrons is inspired by that of Feshbach metastable states in atomic physics. The recent claim of an exotic resonance in the View the MathML source channel by the D0 Collaboration and the negative result presented subsequently by the LHCb Collaboration are understood in this scheme, together with a considerable portion of available data on X,Z particles. Considerations on a state with the same quantum numbers as the X(5568) are also made

Exotic Heavy Quarkonium Spectroscopy: A Mini-review

Since nine years experiments have been observing a host of exotic states decaying into heavy quarkonia. The interpretation of most of them still remains uncertain and, in some cases, controversial, notwithstanding a considerable progress has been made on the quality of the experimental information available and a number of ideas and models have been put forward to explain the observations. In this mini-review we will summarize the measurements, with the most recent updates, and list the useful ones yet to be done. We will discuss the problem of the spin of the X, which could hide some major surprise on its interpretation, and review some more phenomenological issues debated in the field.Comment: 14 pages, 2 figures, 5 tables. To appear in Mod. Phys. Lett.

A Theory of X and Z Multiquark Resonances

We introduce the hypothesis that diquarks and antidiquarks in tetraquarks are separated by a potential barrier. We show that this notion can answer satisfactorily long standing questions challenging the diquark-antidiquark model of exotic resonances. The tetraquark description of X and Z resonances is shown to be compatible with present limits on the non-observation of charged partners X^+-, of the X(3872) and the absence of a hyperfine splitting between two different neutral states. In the same picture, Z_c and Z_b particles are expected to form complete isospin triplets plus singlets. It is also explained why the decay rate into final states including quarkonia are suppressed with respect to those having open charm/beauty states.Comment: 6 pages, 2 figures, some points clarified. To appear in PL