B0bar decays to D(*)0 eta and D(*)0 eta'

We consider the hadronic B decays B0bar -> D0 eta, B0bar -> D*0 eta, B0bar -> D0 eta', B0bar -> D*0 eta' in the framework of a quark-flavour basis and factorization. The formalism allows to compute the decays to the eta meson and to relate them to those of the eta'. Measuring the branching ratios of these processes may shed light on the nature of the eta-eta' mixing. On the experimental side, only upper limits on the branching ratios are known at present.Comment: 12 pages, 2 figures, 2 tables (LaTeX, revtex), minor revision: note added at the end concerning new data and few reference

Jet Shapes in Opaque Media

We present general arguments, based on medium-induced radiative energy loss, which reproduce the non-gaussian shapes of away-side di-jet azimuthal correlations found in nucleus-nucleus collisions at RHIC. A rather simple generalization of the Sudakov form factors to opaque media allowing an effective description of the experimental data is proposed.Comment: 4 pages, 2 ps figure

Tetraquarks in the 1/N expansion and meson-meson resonances

Diquarks are found to have the right degrees of freedom to describe the tetraquark poles in hidden-charm to open-charm meson-meson amplitudes. Compact tetraquarks result as intermediate states in non-planar diagrams of the 1/N expansion and the corresponding resonances are narrower than what estimated before. The proximity of tetraquarks to meson-thresholds has an apparent role in this analysis and, in the language of meson molecules, an halving rule in the counting of states is obtained

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.

Diquark-antidiquark states with hidden or open charm

Some features and predictions of a recently proposed model based on diquark-antidiquark bound states are illustrated. Its ability in accomodating newly discovered charmed resonances around 4 GeV is discussed.Comment: To appear in the proceedings of the HEP2005 International Europhysics Conference on High Energy Physics, July 21st-27th 2005, Lisboa, Portuga

A bbbˉbˉbb\bar b\bar b di-bottomonium at the LHC?

We study the case of a di-bottomonium $bb\bar b\bar b$ particle at the LHC. Its mass and decay width are obtained within a new model of diquark-antidiquark interactions in tetraquarks. The same model solves several open problems on the phenomenology of the experimentally better known $X,Z$ states. We show that the $bb\bar b\bar b$ tetraquark is expected approximately 100 MeV below threshold, and compare to a recent analysis by LHCb seeking it in the $\Upsilon\mu\mu$ final state.Comment: 7 pages, 3 figures. V2: figure added, figures corrected and updated, typo correcte

The lattice Schrödinger functional and the background field effective action

We propose a new method that by using the lattice Schr\"odinger functional allows to investigate the effective action for external background fields in lattice gauge theories. We show that this method gives sensible results for the case of four-dimensional U(1) gauge theory in an external constant magnetic field

Flavored tetraquark spectroscopy

The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quark bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons