Monte-Carlo study of the Deltarho parameter

We present results concerning a lattice study of the electroweak $\rho$-parameter. We have used an SU(2)$\times$U(1) symmetric chiral Yukawa model built with Zaragoza fermions. The decoupling of the species doublers in this model is verified numerically. We find that the numerical data for $\Delta\rho$ are well described by one-loop perturbation theory with the same finite volume and with the same finite cut-off. However, a finite cut-off can cause substantial deviations of $\Delta\rho$ from the standard value, even in infinite volume.