  Lattice field theory is a useful tool for studying strongly interacting
theories in condensed matter physics. A prominent example is the unitary Fermi
gas: a two-component system of fermions interacting with divergent scattering
length. With Monte Carlo methods this system can be studied from first
principles. In the presence of an imbalance (unequal number of particles in the
two components) a sign problem arises, which makes conventional algorithms
inapplicable. We will show how to apply reweighting techniques to generalise
the recently developed worm algorithm to the imbalanced case, and present
results for the critical temperature, the energy per particle, the chemical
potential and the contact density for equal, as well as unequal number of
fermions in the two spin components.
