Glueball-Meson Mixing

Calculations in unquenched QCD for the scalar glueball spectrum have confirmed previous results of Gluodynamics finding a glueball at ~ 1750 MeV. I analyze the implications of this discovery from the point of view of glueball-meson mixing at the light of the experimental scalar sprectrum.Comment: 7 pages, 5 figure

AdS gravity and glueball spectrum

The glueball spectrum has attracted much attention since the formulation of Quantum Chromodynamics. Different approaches give very different results for their masses. We revisit the problem from the perspective of the AdS/CFT correspondence.Comment: 4 pages, no figures, 5 table

Generalized parton distributions and composite constituent quarks

An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as complex systems. The GPDs are obtained from the wave functions of the non relativistic CQM of Isgur and Karl, convoluted with the GPDs of the constituent quarks themselves. The latter are modelled by using the structure functions of the constituent quark, the double distribution representation of GPDs, and a recently proposed phenomenological constituent quark form factor. The present approach permits to access a kinematical range corresponding to both the DGLAP and the ERBL regions, for small values of the momentum transfer and of the skewedness parameter. In this kinematical region, the cross sections relevant to deeply virtual Compton scattering could be estimated by using the obtained GPDs. As an example, the leading twist, unpolarized GPD $H$ has been calculated. Its general relations with the non relativistic definition of the electric form factor and with the leading twist unpolarized quark density are consistently recovered from our expressions.Further natural applications of the proposed approach are addressed.Comment: 38 pages, 8 figures; final, extended version accepted by Phys. Rev.

Generalized parton distributions in constituent quark models

An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario. These off-diagonal distributions are obtained from momentum space wave functions to be evaluated in a given non relativistic or relativized CQM. The general relations linking the twist-two GPDs to the form factors and to the leading twist quark densities are consistently recovered from our expressions. Results for the leading twist, unpolarized GPD, H, in a simple harmonic oscillator model, as well as in the Isgur and Karl model, are shown to have the general behavior found in previous estimates. NLO evolution of the obtained distributions, from the low momentum scale of the model up to the experimental one, is also shown. Further natural applications of the proposed formalism are addressed.Comment: 19 pages, 8 figures, discussion of the Isgur and Karl model added, NLO QCD evolution evaluated, references and figures adde

Scalar and Tensor Glueballs as Gravitons

The bottom-up approach of the AdS/CFT correspondence leads to the study of field equations in an $AdS_5$ background and from their solutions to the determination of the hadronic mass spectrum. We extend the study to the equations of $AdS_5$ gravitons and determine from them the glueball spectrum. We propose an original presentation of the results which facilitates the comparison of the various models with the spectrum obtained by lattice QCD. This comparison allows to draw some phenomenological conclusions.Comment: 9 pages , 5 figure