Strong Interactions at Low Energies

Effective field theories are playing an increasing role in the study of a wide variety of physical phenomena, from W and Z interactions to superconductivity. Regarding the subject of this talk, we have known for years that the low energy strong interactions of nucleons and pions are well described in the tree approximation by an effective field theory, with Lagrangian[1] Leff = − ∂μ~π · ∂~π 2(1 + ~π/F 2 π ) 2 − m 2 π ~π 2 2(1 + ~π/F 2 π ) 2 +N̄ [ i∂0 − 2~t · (~π × ∂0~π) F 2 π (1 + ~π /F 2 π ) 2 −mN − 2gA~t · (σ · ∇)~π Fπ(1 + ~π/F 2 π ) ]