Partially Twisted Boundary Conditions in Lattice Simulations

We use chiral perturbation theory to investigate twisted and partially twisted boundary conditions which allow access to momenta other than integer multiples of 2pi/L on a lattice with spatial volume L^3. For K -> pi pi decays we show that the breaking of isospin symmetry by the twisted boundary conditions implies that the amplitudes cannot be determined in general. We find numerical evidence for the result that the finite volume effects of the boundary conditions are exponentially suppressed for quantities without final state interactions (meson masses and meson-to-vacuum matrix elements) in a simulation with partial twisting on a sea of N_f=2 non-perturbatively improved Wilson quarks.