Universal amplitude ratios for scaling corrections on Ising strips with fixed boundary conditions

We study the (analytic) finite-size corrections in the Ising model on the strip with fixed (+-) boundary conditions. We find that subdominant finite-size corrections to scaling should be to the form ak/N2k-1 for the free energy fN and bk(n)/N2k-1 for inverse correlation length ξn-1, with integer value of k. We investigate the set {ak,bk(n)} by exact evaluation and their changes upon varying anisotropy of coupling. We find that the amplitude ratios bk(n)/ak remain constant upon varying coupling anisotropy. Such universal behavior are correctly reproduced by the conformal perturbative approach.