  A mass parameter for the gauge bosons in gauge-fixed four-dimensional
Yang-Mills theory can be accommodated in a local and manifestly BRST-invariant
action. The construction is based on the Faddeev-Popov method involving a
nonlinear gauge-fixing and a background Nakanishi-Lautrup field. When applied
to momentum-dependent masslike deformations, this formalism leads to a full
regularization of the theory which explicitly preserves BRST symmetry. We
deduce a functional renormalization group equation for the
one-particle-irreducible effective action, which has a one-loop form. The
master equation is compatible with it, i.e. BRST symmetry is preserved along
the flow, and it has a standard regulator-independent Zinn-Justin form. As a
first application, we compute the leading-order gluon wave-function
renormalization.
