NSVZ scheme with the higher derivative regularization for N=1 SQED

The exact NSVZ relation between a $\beta$-function of ${\cal N}=1$ SQED and an anomalous dimension of the matter superfields is studied within the Slavnov higher derivative regularization approach. It is shown that if the renormalization group functions are defined in terms of the bare coupling constant, this relation is always valid. In the renormalized theory the NSVZ relation is obtained in the momentum subtraction scheme supplemented by a special finite renormalization. Unlike the dimensional reduction, the higher derivative regularization allows to fix this finite renormalization. This is made by imposing the conditions $Z_3(\alpha,\mu=\Lambda)=1$ and $Z(\alpha,\mu=\Lambda)=1$ on the renormalization constants of ${\cal N}=1$ SQED, where $\Lambda$ is a parameter in the higher derivative term. The results are verified by the explicit three-loop calculation. In this approximation we relate the $\bar{{DR}}$ scheme and the NSVZ scheme defined within the higher derivative approach by the finite renormalization.