Few-body systems with resonant short-range interactions display universal
properties that do not depend on the details of their structure or their
interactions at short distances. In the three-body system, these properties
include the existence of a geometric spectrum of three-body Efimov states and a
discrete scaling symmetry. Similar universal properties appear in 4-body and
possibly higher-body systems as well. We set up an effective theory for
few-body systems in a harmonic trap and study the modification of universal
physics for 3- and 4-particle systems in external confinement. In particular,
we focus on systems where the Efimov effect can occur and investigate the
dependence of the 4-body spectrum on the experimental tuning parameters.Comment: 20 pages, 10 figures, final version, new references adde
