ar X iv : h ep - p h / 02 11 22 5 v 1 1 4 N ov 2 00 2 The Ideal Mixing Departure in Vector Meson Physics

In this work we study the departure for the ideal φ − ω mixing angle in the frame of the Nambu-Jona-Lasinio model. We have shown that in that context, the flavour symmetry breaking is unable to produce the shifting in the mixing angle. We introduce a nonet symmetry breaking in the neutral vector sector to regulate the non-strange content of the φ meson. The phenomenon is well reproduced by our proposal. It is well known that it is not possible to use perturbative expansions of QCD to describe low energy hadronic phenomena. For that reason, a great deal of effective theories, preserving the symmetries of QCD, have been developed to account for the main properties of hadrons. One of the basic aspects common to both schemes, is the chiral invariance of the strong interactions in the massless limit. This symmetry is explicitly broken if quarks are massive. Chiral effective models [1] have demonstrated to reproduce the low energy hadron phenomena. The effective four fermion Lagrangian, proposed by Nambu-Jona-Lasinio (NJL) [2], is an intermediate step between QCD and effective mesons theories. From NJL Lagrangian is it possible to obtain an effective meson Lagrangian after proper bosonization [3]. The NJL model is a profitable arena to study various phenomena related to symetry brak-down in hadron physics. In particular, the ω − φ mixing was largely studied by theoretical and experimental points of view since the begining of the sixties [4]. Measurements show that the φ meson decays into π + π − , violating isospin conservation and OZI rule [5,6]. In the present paper we will study the departure of the ω − φ ideal mixing angle in the NJL model, allowing a non strange content in the φ meson. We will focus our attention in the vector meson sector where the phenomenology we are interested to describe takes place. It is important to note that, in the framework of most theoretical models, the ρ and ω mesons are composed by u and d light quarks, whereas the quark content of φ meson is purely strange, which do not coincide with experimental data [7]. Let us note that some authors predict the departure from ideal mixing angle whithin different approaches [8–10]. Our purpose is to explore the origin of the shifting in the φ − ω mixing angle in the frame of the NJL Lagrangian and its connection with chiral symmetry. The …