On multi-particle functions and pion-decay constant in Nambu--Jona-Lasinio model
Rochev, V. E.
Original · EN
The system of second-order equations of mean-field expansion is considered for Nambu--Jona-Lasinio model with chiral symmetry of SU(2)-group. The system includes equations for four-particle and three-particle functions and also equations for next-to-leading two-particle function and next-to-next-to-leading quark propagator. Exact solutions for four-particle and three-particle equations are obtained. The solution for four-particle function is a disconnected combination of the leading-order two-particle functions. The connected part of three-particle function includes two-meson and three-meson contributions. The solution of three-particle equation permits to close the equation for next-to-leading two-particle function and to calculate a correction to pion-decay constant fπ. This correction increases from 14% to 28% when values of quark condensate varies from -(210 MeV)³ to -(250 MeV)³.
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