In this study, the proton is taken as an ensemble of quark-gluon Fock states. Using the principle of balance that every Fock state should be balanced with all of the nearby Fock states (denoted as the balance model), instead of the principle of detailed balance that any two nearby Fock states should be balanced with each other (denoted as the detailed balance model), the probabilities of finding every Fock state of the proton are obtained. The balance model can be taken as a revised version of the detailed balance model, which can give an excellent description of the light flavor sea asymmetry (i.e., u = d) without any parameter. In case of g ⇔ gg sub-processes not considered, the balance model and the detailed balance model give the same results. In case of g ⇔ gg sub-processes considered, there is about 10 percent difference between the results of these models. We also calculate the strange content of the proton using the balance model under the equal probability assumption.

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A vector coupling term apart from the scalar and psendoscalar terms, is introduced into the nonlocal quark-(anti-)quark interaction in an extended Nambu-Jona-Lasinio model to investigate the vector rho meson mode in the relativistic random phase approximation (RPA). It is shown that a favorabJe choice of the vector coupling to fit the empirical data has to be the same form as that of the original scalar and pseudoscalar ones but with a necessary negative sign.

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