%0 Journal Article %T Nonperturbative renormalization-group approach to fermion systems in the two-particle-irreducible effective action formalism %A N. Dupuis %J Physics %D 2013 %I arXiv %R 10.1103/PhysRevB.89.035113 %X We propose a nonperturbative renormalization-group (NPRG) approach to fermion systems in the two-particle-irreducible (2PI) effective action formalism, based on an exact RG equation for the Luttinger-Ward functional. This approach enables us to describe phases with spontaneously broken symmetries while satisfying the Mermin-Wagner theorem. We show that it is possible to choose the Hartree-Fock--RPA theory as initial condition of the RG flow and argue that the 2PI-NPRG is not restricted to the weak-coupling limit. An expansion of the Luttinger-Ward functional about the minimum of the 2PI effective action including only the two-particle 2PI vertex leads to nontrivial RG equations where interactions between fermions and collective excitations naturally emerge. %U http://arxiv.org/abs/1310.4979v2