  We examine the physics of two, three, and four heavy fermions interacting
with a single light fermion via short-range interactions. Four-particle bosonic
Efimov states have proven important experimentally and also been the subject of
significant theoretical effort. Similar fermionic systems are just now being
investigated. We find that with some simple interactions the four- and
five-particle states collapse to the interaction range at smaller mass ratios
than the three-body state, and also before larger clusters can collapse. These
states and their excitations can be studied in cold atom experiments, providing
unique insights into the role of few-body systems in many-body physics.
