Higher-order fermion effective interactions in a bosonization approach

Abstract

Three different fermion effective potentials given by series of bilinears, $\sum\nolimits_j^N {\left( {\bar \psi _a \psi _a } \right)^{2^j } ,} \sum\nolimits_j^N {\left( {\bar \psi _a \psi _a } \right)} ^j$ and also $\sum\nolimits_j^N {\left( {\bar \psi _a \gamma _\mu \psi _a } \right)} ^{2j}$, where a = 1, ... N _r and integer j, are investigated by introducing sets of auxiliary fields. A mininal procedure is adopted to deal with the auxiliary fields and an effective bosonized model in each case is found by assuming weak field fluctuations, i.e. weak enough when compared to (normalized) coupling constants. Different fermion condensates are considered for the ground state in the first two series analysed and the factorization of all higher-order condensates into the lowest-order one is found in most cases, i.e. in general $\left\langle {\left( {\bar \psi _a \psi _a } \right)^n } \right\rangle \propto \left\langle {\bar \psi _a \psi _a ^n } \right\rangle$. For the third series built with vector-type bilinears no condensation is assumed to occur. The corresponding (weak) scalar fields effective models for the three cases are expanded in polynomial interactions. The resulting low-energy effective boson model may exhibit a new approximate symmetry depending on the terms present in the original series model and on the values of the coupling constants.