A New, exact, gauge invariant RG flow equation

We introduce a scale-dependent effective action defined through a partial Legendre transform first discussed by Zumino more than 30 years ago. This new effective action depends, at any scale, on all degrees of freedom, is gauge-invariant/general-covariant, and obeys a simple, exact and manifestly gauge-invariant RG-flow equation. It should be useful in a variety of problems, including some pertaining to non-abelian gauge theories and quantum gravity. Pacs 11.10.Hi , 11.10.Gh , 11.15Tk Vincenzo.Branchina@ires.in2p3.fr Krzysztof.Meissner@fuw.edu.pl Gabriele.Veneziano@cern.ch