A New Picture of Structure of Meson

Quark model and parton model are the two models of hadrons. In this talk a unified model of meson structure is presented. Based on current algebra and chiral symmetry a chiral field theory of pseudoscalar, vector, axial-vector mesons is constructed. Both constituent and current quark masses appear in the same theory. Quark condensation, $N_C$ expansion, and chiral symmetry are embedded. Besides three current quark masses there are two parameters. The theory is phenomenologically successful. A brief review of the achievements is presented. In this talk we emphasize the new picture of the structure of pion. $m^2_\pi$ is derived. Pion form factor is predicted, which is in excellent agreement with data in both space-like and time-like regions. A new asymptotic pion form factor $F(Q^2)|_{Q^2\rightarrow\infty}$ is obtained. The pion structure is revealed: \begin{enumerate} \item when $q^2 < m^2_\rho$ pion is made of a pair of constituent quarks: $q\bar{q}$ \item when $q^2 > m^2_\rho$ pion is made of a pair of constituent quarks plus $\rho$ cloud multi- quark pairs \item at large $q^2$ pion is made of a pair of constituent quarks plus a hard gluon \end{enumerate} Similar structures for kaons and other mesons are presented.