  We measure the energy levels of the excitations of the flux tube between
static quark and antiquark in three-dimensional SU(2) gauge theory. Combining
exponential error reduction techniques and a variational method we are able to
reduce the errors for the excited states significantly and to extract excited
states in distinct parity and charge conjugation channels. It is conjectured
that the infrared behavior (at large q\bar{q} separation R) of the flux tube is
governed by an effective string theory. Indeed previous simulations show good
agreement between lattice data and predictions from Nambu-Goto string theory.
Recently, new results on the effective string theory obtained corrections to
the Nambu-Goto predictions and showed that for the open string in three
dimensions first corrections should appears at order 1/R^4. They correspond to
boundary terms in the worldsheet field theory. These corrections are presumably
small for the ground state, but significantly larger for the excited states and
lift the degeneracies of the free theory. Assuming this functional form of the
correction, we obtain for the coefficient b_2=-0.5(2)(2).
