Dynamical bag in a chiral quark model

A type of bag function is proposed to make the MIT bag surface of baryon dynamical. It is illustrated through renormalization of the quark field that the softening of chiral bag gives rise to a model of chiral quark with effectively-generated mass of quark, in which confined quark moves in the background of nonlinear pion. A prediction of bag constant $B$ $\simeq 2f_{\pi}^{2}m_{\pi}^{2}\allowbreak $ is made. With two free parameters, the self-coupling $e$ of pion and the confining scale $a$, the computed mass, the charge root-mean-square radius and magnetic moment of the proton are in good agreement with the experimental values.