In this work we have applied the coupled-channel formalism incorporating quasi-bound quark-model states to the description of scattering and electro-production of mesons in the D13, D33 and D15 partial waves. In contrast to our results for the P11, P33 and S11 resonances, the underlying quark model predicts for the D-wave resonances a too weak coupling of quarks to the pion with l=2 and the photon. The resulting helicity amplitudes and consequently the meson electro-production amplitudes turn out to be too small compared to the experiment -- though in accordance with other quark model calculations. Nonetheless, our calculation exhibits a consistent overall qualitative agreement with the multipole analysis in the D13, D33 and D15 partial waves. Furthermore, our results, in particular for the D33 wave, show that the meson cloud effects are important in describing the long-range part of the wave-function. We expect that a more elaborate description of the quark core, supplemented by the meson cloud, may eventually bring the results in the ballpark of acceptable values.
COBISS.SI-ID: 2581860
Known hadrons are composed of three valence quarks (barions) and valence quark-antiquark pair (mesons). Belle collaboration discovered an interesting state X(3872) in 2003, which is most likely a mesonic molecule D0-bar D*0. In spite of many attempts to provide theoretical evidence for the existence of this interesting state, our results present the first unambiguous evidence for its existence within the framework of ab-initio lattice QCD. We find a state in a dynamical simulation of scattering D-bar D* in the channel with J+=1++ and I=0. This is the first simulation that establishes a candidate for X(3872) in addition to the nearby scattering states D -bar D* and J/psi mega, which inevitably have to be present in dynamical QCD. The D-bar D* scattering phase shift is extracted using the Luscher formalism and we find large and negative D-bar D* scattering length a0=-1.7+- 0.4 fm. The extrapolation of the resulting phase shift indicates a pole 11+- 7 MeV below DD* threshold and we relate this pole to experimental near-threshold state X(3872). The detailed study of the composition of the resulting state indicates a large D-bar D* component, as supported by the previous phenomenological studies claiming that this is a mesonic molecule.
COBISS.SI-ID: 2613348
Explanation of a too large measured branching fraction of decays B -) D tau nu in B -) D* tau nu, measured by the BaBar collaboration, is still not known. We have studied a scenario with an addition of a single scalar particle that couples to quarks and leptons. We have endowed this leptoquark with quantum number (3,2,7/6) and a minimal set of flavor coupling that suffices to explain the B -) D(*) tau nu anomaly and is consistent with constraints from other processes. These are decay Z -) b anti-b, lepton flavor violating decays (e.g. mu -) e gamma), and magnetic and electric dipole moments. In the framework of a Grand unified theory we have predicted correlations between various decay channels of proton, as well as rare decays of t-quark and D meson.
COBISS.SI-ID: 27276327
We study the transition of a scalar field in a fixed AdS (d+1) background between an extremum and a minimum of a potential. We compute analytically the solution to the perturbation equation for the vev deformation case by generalizing the usual matching method to higher orders and find the propagator of the boundary theory operator defined through the AdS-CFT correspondence. We show that, contrary to what happens at the leading order of the matching method, the next-to-leading order presents a simple pole at q ^2 = 0 in accordance with the Goldstone theorem applied to a spontaneously broken dilatation invariance.
COBISS.SI-ID: 27392295