Sea Contributions to Hadron Electric Polarizabilities through   Reweighting
  As part of our ongoing lattice study of the electric polarizabilities of hadrons using the background field approach, we use reweighting to examine the effect of the field on the sea quarks. As with other reweighting studies, the chief difficulty lies in the construction of a stochastic estimate of the ratio of the fermion determinants. In contrast to the case of reweighting in the quark mass, these estimators converge extremely slowly, and are resistant to common variance-reduction techniques such as low-mode subtraction. However, it is possible to construct an alternate estimator, taking advantage of the fact that we are interested in only perturbatively small fields; this estimator is susceptible to a variance-reduction technique based on a hopping parameter expansion. 
Walter Freeman, Andrei Alexandru, Frank Lee, Michael Lujan
hep-lat