Abstract. Fermionic functional renormalization group is applied to describe Bose--Einstein condensation of composite dimers in a two-component fermionic system with a short-range interaction. Since fermions are bounded in dimers, they do not affect long-range nature of the system. This requires us to invent a renormalization group procedure, which controls the dispersion relation of composite bosons without affecting that of fermionic excitations. In order to realize it without introducing auxiliary bosonic fields, we introduce a vertex infrared regulator so as to compute the critical temperature.

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