One-loop anisotropy for improved actions

We determine the one-loop correction to the anisotropy factor for the square Symanzik improved lattice action, extracted from the finite volume effective action for SU(N) gauge theories in the background of a zero-momentum gauge field. The result is smaller by approximately a factor 3 than the one-loop correction for the anisotropic Wilson action. We also comment on the Hamiltonian limit.