Multiquark structures in heavy-light meson systems * J. Vijande ab , A. Valcarce a , F. Fern´ andez a a Grupo de F´ ısica Nuclear and IUFFyM, Universidad de Salamanca, E-37008 Salamanca,Spain b Dpto. de F´ ısica Te´orica. Universidad de Valencia - CSIC, E-46100 Burjassot, Valencia, Spain. We look for possible signatures of multiquark structures in the heavy-light meson spec- tra. The controversial D * s0 (2317) and D * s1 (2460) states are properly described if con- sidered as a mixture of conventional P-wave q ¯ q and four-quark components. The re- cently discovered D * sJ (2860) appears as the orthogonal partner of the D * s0 (2317). Similar structures are predicted in the B s sector. We also consider the possible existence of iso- lated I = 1 four-quark resonances and we argue that their existence can disentangle the Υ(nS ) → Υ(mS )ππ decay puzzle 1. INTRODUCTION During the last years the discovery of several new charmed mesons had a deep impact in hadron physics. The observation of two narrow resonances, D * s0 (2317) and D * s1 (2460), with unexpected properties, quite different from those predicted by quark potential models, has raised a lot of discussion about the nature of these states and their quark content. The recent observation of two new meson states, the D * sJ (2860) announced by BaBar collaboration [1] and the D * sJ (2715) announced by Belle collaboration[2], provided with another interesting piece of information about the heavy light mesons and opened the possibility to study mesons beyond the conventional q ¯ q structure. Physical mesons are easily identified with q ¯ q states when virtual quarks loops are not important. This is the case of the pseudoscalar and vector mesons due to the P-wave nature of the loop dressing. On the contrary in the scalar sector the q ¯ q pair is in a P-wave state, whereas the contributing quark loops are in an S-wave. In this case the coupling between q ¯ q pairs and qq ¯ q ¯ q structures may be relevant. Another situation in which a four- quark configuration may be important is the description of open-charm (or open-bottom) states with isospin I = 1, a value that can only be reached if more than one light quark is present. Most of the multiquark resonances would appear in nature coupled to the corresponding q ¯ q pairs. Therefore one needs a model that can describe simultaneously two- and four- quark states as well as their coupling. We will use the model of Ref. [3], that generates * This work has been partially funded by Ministerio de Ciencia y Tecnolog´ ıa under Contract No. FPA2004- 05616, and by Junta de Castilla y Le´ on under Contract No. SA-104/04. Nuclear Physics A 790 (2007) 506c–509c 0375-9474/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2007.03.114