Heavy baryon chiral perturbation theory

Heavy baryon chiral perturbation theory (HBChPT) is an effective quantum field theory used to describe the interactions of pions and nucleons/baryons. It is somewhat an extension of chiral perturbation theory (ChPT) which just describes the low-energy interactions of pions. In a richer theory one would also like to describe the interactions of baryons with pions. A fully relativistic Lagrangian of nucleons is non-predictive as the quantum corrections, or loop diagrams can count as O ( 1 ) {displaystyle {mathcal {O}}(1)} quantities and therefore do not describe higher-order corrections. Heavy baryon chiral perturbation theory (HBChPT) is an effective quantum field theory used to describe the interactions of pions and nucleons/baryons. It is somewhat an extension of chiral perturbation theory (ChPT) which just describes the low-energy interactions of pions. In a richer theory one would also like to describe the interactions of baryons with pions. A fully relativistic Lagrangian of nucleons is non-predictive as the quantum corrections, or loop diagrams can count as O ( 1 ) {displaystyle {mathcal {O}}(1)} quantities and therefore do not describe higher-order corrections. Because the baryons are much heavier than the pions, HBChPT rests on the use of a nonrelativistic description of baryons compared to that of the pions. Therefore, higher order terms in the HBChPT Lagrangian come in at higher orders of m B − n {displaystyle m_{B}^{-n}} where m B {displaystyle m_{B}} is the baryon mass.