Effective approaches to meson structure
Tanja Branz (Universität Tübingen)

Effective models are a valuable tool to get further information on hadron structure. Recently, the hidden charm spectrum came into the focus of interest due to the discovery of the charmonium-like X,Y and Z mesons. Since these states cannot be easily explained by the standard quarkonium assignment these unusual resonances can possibly offer new insights into the issue of meson structure.

We study the structure of the Y(3940), Y(4140) and Z+(4430) mesons as bound states of charmed mesons [1,2]. In particular we discuss a possible interpretation of the Y(3940) and Y(4140) mesons as hadronic molecules, where the Y(3940) state is considered as a superposition of D*(+)D*(-) and D*(0) D*(0)bar, while the Y(4140) is a bound state of Ds*(+) and Ds*(-) mesons. The Z+ is a special case since a conventional quark-antiquark structure can be ruled out. The Z+ is assumed to be composed of a D* and the axial D_1(2420).

We analyze the hidden charm and radiative decay properties in an effective Lagrangian approach and test our predictions with available data.

Besides the above mentioned method based on effective Lagrangians we also use a holographic AdS/QCD approach to get further insight into hadron structure. As a first application we calculated the mass spectrum and decay constants of conventional mesons made up of a valence quark-antiquark pair [3]. In this context we studied mesons ranging from the light to the double heavy quark sector.

[1] Tanja Branz, Thomas Gutsche and Valery E. Lyubovitskij, Phys. Rev. D 80, 054019 (2009)
[2] Tanja Branz, Thomas Gutsche and Valery E. Lyubovitskij, Phys. Rev. D 82, 054025 (2010)
[3] Tanja Branz, Thomas Gutsche and Valery E. Lyubovitskij, arXiv:1008.0268 (2010)