On the nature of the X(3872)

We present recent studies of charmonium multiquark states. We use different interacting models and numerical methods to study deeply bound four-quark states and meson-meson molecules. No deeply bound four-quark states are found in our analysis. A nice description of the X(3872) is obtained as a $D\bar{D}^*-J/\Psi\omega$ coupled channel state.Comment: 3 pages. Talk presented at the Conference MESON 2010, 10-15 june 2010, Krakow, Poland. To be published in International Journal of Modern Physics

Stability of hexaquarks in the string limit of confinement

The stability of systems containing six quarks or antiquarks is studied within a simple string model inspired by the strong-coupling regime of quantum chromodynamics and used previously for tetraquarks and pentaquarks. We discuss both six-quark $(q^6)$ and three-quark--three-antiquark $(q^3\bar q{}^3)$ states. The quarks are assumed to be distinguishable and thus not submitted to antisymmetrization. It is found that the ground state of $(q^6)$ is stable against dissociation into two isolated baryons. For the case of $(q^3\bar q{}^3)$, our results indicate the existence of a bound state very close to the threshold. The investigations are extended to $(q^3Q^3)$ and $(Q^3\bar q^3)$ systems with two different constituent masses, and their stability is discussed as a function of the mass ratio.Comment: 7pages, 7 figure

Heavy-baryon quark model picture from lattice QCD

The ground state and excited spectra of baryons containing three identical heavy quarks, b or c, have been recently calculated in nonperturbative lattice QCD. The energy of positive and negative parity excitations has been determined with high precision. Lattice results constitute a unique opportunity to learn about the quark-confinement mechanism as well as elucidating our knowledge about the nature of the strong force. We analyze the nonperturbative lattice QCD results by means of heavy-quark static potentials derived using SU(3) lattice QCD. We make use of different numerical techniques for the three-body problem

Stability of Multiquarks in an Improved Flip-Flop Model of Confinement

We review some recent studies on the string model of confinement inspired by the strong-coupling regime of QCD and its application to exotic multiquark configurations. This includes two quarks and two antiquarks, four quarks and one antiquark, six quarks, and three quarks and three antiquarks with a careful treatment of the corresponding few-body problem

Describing non-QQ candidates

Despite the apparent simplicity of meson spectroscopy there are some states which cannot be accommodated in the usual q (q) over bar structure. Among them there are either exotic states as the X(1600) or the recently measured charm states D-sJ(*) and X(3872) and some of the light scalar mesons. In this work we present a possible description of these states in terms of tetraquarks

Adiabaticity and color mixing in tetraquark spectroscopy

We revisit the role of color mixing in the quark model calculation of tetraquark states, and compare simple pairwise potentials to more elaborate string models with three-and four-body forces. We attempt to disentangle the improved dynamics of confinement from the approximations made in the treatment of the internal color degrees of freedom

Towards the understanding of the meson spectra

We present a quark-quark interaction for the complete study of the meson spectra, from the light to the heavy sector. We compare the quark model predictions against well-established q (q) over bar experimental data. This allows to identify discrepancies between quark model results and experiment that may signal physics beyond conventional hadron spectroscopy

Evaluation of dosimetric effects of metallic artifact reduction and tissue assignment on Monte Carlo dose calculations for 125 I prostate implants

Methods The geometry of the IsoSeed I25.S17plus source is validated by comparing the MC calculated results of the TG-43 parameters for the line source approximation with the TG-43U1S2 consensus data. Four MC absorbed dose calculations are performed in two virtual patient models using the egs_brachy MC code: (1) TG-43-based Dw,w-TG 43 , (2) Dw,w-MBDC that accounts for interseed scattering and attenuation (ISA), (3) Dm,m that examines ISA and tissue heterogeneity by scoring absorbed dose in tissue, and (4) Dw,m that unlike Dm,m scores absorbed dose in water. The MC absorbed doses (1) and (2) are simulated in a TG-43 patient phantom derived by assigning the densities of every voxel to 1.00 g cm-3 (water), whereas MC absorbed doses (3) and (4) are scored in the TG-186 patient phantom generated by mapping the mass density of each voxel to tissue according to a CT calibration curve. The MC absorbed doses calculated in this study are compared with VariSeed v8.0 calculated absorbed doses. Results The very good agreement of TG-43 parameters of this study and the published consensus data within 3% validates the geometry of the IsoSeed I25.S17plus source. For the clinical studies, the TG-43-based calculations show a D90 overestimation of more than 4% compared to the more realistic MC methods due to ISA and tissue composition. The results of this work generally show few discrepancies with the post-implant CT-based dosimetry studies with respect to the D90 absorbed dose metric parameter. These discrepancies are mainly Type B uncertainties due to the different 125 I source models and MC codes. Conclusions The implementation of MAR and TAS on post-implant CT images have no dosimetric effect on the 125 I prostate MC absorbed dose calculation in post-implant CT-based phantoms