Lagrange multiplier field approach to shift-symmetric theories: the $\varphi^4$ derivative theory and the crumpled-to-flat transition of membranes at two-loop order

We introduce a technique relying on the use of Lagrange multiplier field in order to eliminate explicit field-derivatives that plague the high orders renormalization group treatment of shift-symmetric, derivative, theories. This technique simplifies drastically the computation of fluctuations in such theories. This is illustrated by deriving the two-loop renormalization group equations and the three-loop anomalous dimension of the $\varphi^4$ derivative theory in $D=4-\epsilon$, which is also relevant to describe the crumpled-to-flat transition of polymerized membranes. Some features of this transition are provided.