The Wilson-Fisher Fixed point revisited: importance of the form of the cutoff

Abstract: In this work we re-examine the Wilson Fisher fixed point. We study Wilsonian momentum space renormalization group (RG) flow for various forms of the cutoff. We show that already at order $\left(4-d\right)^{1}$, where $d$ is the dimension of the $\phi^{4}$ theory, there are changes to the position of the fixed point and the direction of irrelevant coupling parameters. We also show in a multi-flavor $\phi^{4}$ model that symmetries of the Lagrange function can be destroyed if the different flavors have different cutoffs (that is the Lagrangian can flow to a non-symmetric fixed point). Some related comments are made about a similar situation in parquet RG (pRG). In future works we will study Wilsonian RG to order $\left(4-d\right)^{2}$ and find non-universal critical exponents that depend on the cutoff.