  We study the formation of bound states in a one-dimensional, single-component
Fermi chain with attractive interactions. The phase diagram, computed from DMRG
(density matrix renormalization group), shows not only a superfluid of paired
fermions (pair phase) and a liquid of fermion triplets (trion phase), but also
a phase with two gapless modes. We show that the latter phase is described by a
2-component Tomonaga-Luttinger liquid (TLL) theory, consisting of one charged
and one neutral mode. We argue based on our numerical data, that the single,
pair, and trion phases are descendants of the 2-component TLL theory. We
speculate on the nature of the phase transitions amongst these phases.
