Higher-order fermion interactions in effective field theories for phase transitions

We investigate the impact of higher-order fermionic deformations in phase transitions analogous to those described by the Bardeen–Cooper–Schrieffer (BCS) theory. Focusing specifically on the 8-fermion interaction, we show that this term can have significant consequences. In certain regions of parameter space, the theory continues to exhibit second-order phase transitions with mean-field critical exponents and the same critical temperature; however, the temperature dependence of the superconducting gap can deviate markedly from conventional BCS behavior. In other regions, the theory exhibits first-order phase transitions. We conclude by discussing potential phenomenological applications of these theories.