On reweighting for twisted boundary conditions

Preprint number: CP3-Origins-2016-32 DNRF90
Authors: Andrea Bussone (CP3-Origins & DIAS), Martin Hansen (CP3-Origins & DIAS), Michele Della Morte (CP3-Origins & DIAS), and Claudio Pica (CP3-Origins & DIAS)
External link: arXiv.org

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We consider the possibility of using reweighting techniques in order to correct
for the breaking of unitarity when twisted boundary conditions
are imposed on valence fermions in simulations of lattice gauge theories.
We start by studying the properties of reweighting factors and their variances at tree-level.
That leads us to the introduction of a factorization for the fermionic reweighting determinant.
In the numerical, stochastic, implementation of the method, we find that
the effect of reweighting is negligible in the case of large volumes
but it is sizeable when the volumes are small and the twisting angles are large.
More importantly, we find that for unimproved Wilson fermions, and in small volumes,
the dependence of the critical quark mass on the twisting angle
is quite pronounced and results in large violations of the continuum dispersion relation.