Ruggero Ferrari, Andrea Quadri, “Weak Power-Counting Theorem for the Renormalization of the Nonlinear Sigma Model in Four Dimensions”, Int J Theor Phys, 45, № 12, 2006, 2497
M Lakshmanan, “Nonlinear chiral dispersive waves”, J. Phys. A: Math. Nucl. Gen., 7, № 8, 1974, 889
DANIELE BETTINELLI, RUGGERO FERRARI, ANDREA QUADRI, “FURTHER COMMENTS ON THE SYMMETRIC SUBTRACTION OF THE NONLINEAR SIGMA MODEL”, Int. J. Mod. Phys. A, 23, № 02, 2008, 211
Ruggero Ferrari, “Endowing the nonlinear sigma model with a flat connection structure: a way to renormalization”, J. High Energy Phys., 2005, № 08, 2005, 048