  We theoretically discuss the possible condensation of Cooper triples, which
correspond to a three-body version of Cooper pairs, in three-component Fermi
systems with three-body attractive interactions. A macroscopic number of Cooper
triples can occupy a zero center-of-mass momentum state in the presence of a
Fermi surface of constituent particles, even though the three-body operator
exhibits anti-commutation relation associated with the Fermi-Dirac statistics.
Such a condensation with internal degrees of freedom is similar to bosonization
in a system of infinite-component fermions. We propose a variational wave
function for condensed Cooper triples and show that in the ground state, the
condensed state is energetically favored compared to the normal state. Also, we
discuss effects of the Fermi-surface distortion in a lattice system described
by a three-component Hubbard model.
