No Arabic abstract
We study the self-energy of the SU(3) antidecuplet coming from two-meson virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet representation with N(1710) as nucleon partner, we derive effective Lagrangians that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave. It is found that the self-energies for all members of the antidecuplet are attractive, and the larger strangeness particle is more bound. From two-meson cloud, we obtain about 20 % of the empirical mass splitting between states with different strangeness.
Starting from a molecular picture for the X(3872) resonance, this state and its J^{PC}=2++ HQSS partner [X2(4012)] are analyzed within a model which incorporates possible mixings with 2P charmonium states. Since it is reasonable to expect the bare chi_{c1}(2P) to be located above the Dbar D* threshold, but relatively close to it, the presence of the charmonium state provides an effective attraction that will contribute to bind the X(3872), but it will not appear in the 2++ sector. Indeed in this latter sector, the chi_{c2}(2P) should provide an effective small repulsion, because it is placed well below the D*bar D* threshold. We show how the 1++ and 2++ bare charmonium poles are modified due to the D(*)bar D(*) loop effects, and the first one is moved to the complex plane. The meson loops produce, besides some shifts in the masses of the charmonia, a finite width for the 1++ dressed charmonium state. On the other hand, the X(3872) and X2(4012) start developing some charmonium content, which is estimated by means of the compositeness Weinberg sum-rule. We also show that for X(3872) molecular probabilities of around 70-90 %, the X2 resonance destabilizes and disappears from the spectrum, becoming either a virtual state or being located deep into the complex plane, with decreasing influence in the D* bar D* scattering line.
We study the electromagnetic structure of the nucleon within a hybrid constituent-quark model that comprises, in addition to the $3q$ valence component, also a $3q$+$pi$ non-valence component. To this aim we employ a Poincare-invariant multichannel formulation based on the point-form of relativistic quantum mechanics. With a simple 3-quark wave function for the bare nucleon, i.e. the $3q$-component, we obtain reasonable results for the nucleon form factors and predict the meson-cloud contribution to be significant only below $Q^2lesssim 0.5$,GeV$^2$ amounting to about 10% for $Q^2rightarrow 0$, in accordance with the findings of other authors.
The axial form factor as well as the axial charge of octet baryons are studied in the perturbative chiral quark model (PCQM) with the quark wave functions predetermined by fitting the theoretical results of the proton charge form factor to experimental data. The theoretical results are found, based on the predetermined quark wave functions, in good agreement with experimental data and lattice values. This may indicate that the electric charge and axial charge distributions of the constituent quarks are the same. The study reveals that the meson cloud plays an important role in the axial charge of octet baryons, contributing 30%-40% to the total values, and strange sea quarks have a considerable contribution to the axial charge of the $Sigma$ and $Xi$.
The challenges with the molecular model of the multiquark systems are the identification of the hadronic molecules and the interaction between two color neutral hadrons. We study the di-hadronic molecular systems with proposed interaction potential as s-wave one boson exchange potential along with Screen Yukawa-like potential, and arrived with the proposal that within hadronic molecule the two color neutral hadrons experience the dipole-like interaction. The present study is the continuation of our previous study cite{arxiv-Rathaud-penta}. With the proposed interaction potential, the mass spectra of $Sigma_{s}K^{*}$, $Sigma_{c}K^{*}$, $Sigma_{b}K^{*}$, $Sigma_{s}D^{*}$, $Sigma_{c}D^{*}$, $Sigma_{b}D^{*}$, $Sigma_{s}B^{*}$, $Sigma_{c}B^{*}$, $Sigma_{b}B^{*}$, $Xi_{s}K^{*}$, $Xi_{c}K^{*}$, $Xi_{b}K^{*}$, $Xi_{s}D^{*}$, $Xi_{c}D^{*}$, $Xi_{b}D^{*}$, $Xi_{s}B^{*}$, $Xi_{c}B^{*}$, $Xi_{b}B^{*}$ meson-baryon molecules are predicted. The Weinberg compositeness theorem which provides clue for the compositeness of the state is used for determination of the scattering length and effective range. The present study predict $P_{c}(4450)$ pentaquark sate as $Sigma_{c}D^{*}$ molecule with $I(J^{P})=frac{1}{2}(frac{3}{2}^{-})$. The formalism also predicts some very interesting open as well as hidden flavour near threshold molecular pentaquark states.
We consider meson-baryon interactions in S-wave with strangeness -1. This is a non-perturbative sector populated by plenty of resonances interacting in several two-body coupled channels.We study this sector combining a large set of experimental data. The recent experiments are remarkably accurate demanding a sound theoretical description to account for all the data. We employ unitary chiral perturbation theory up to and including cal{O}(p^2) to accomplish this aim. The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of the two Lambda(1405) resonances and of the Lambda(1670), Lambda(1800), Sigma(1480), Sigma(1620) and Sigma(1750). We finally argue about our preferred solution.