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. I 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 and other
thermodynamic observables at the critical point, namely the chemical
potential, the energy per particle and the contact density. I will also
present some preliminary results for these observables at temperatures
beyond the critical point.