Analysis of Mass Difference of the π and ρ with Bethe–Salpeter Equation

The one-pion exchange force in addition to the one-gluon exchange force is taken into account to study the mass difference of the π and ρ mesons with the Bethe–Salpeter equation. After projecting the Bethe–Salpeter equation into a simple form, it can be seen explicitly that the bound energy |E_π|≫|E_ρ|.