  Recent work has used a U(1) gauge theory to describe the physics of Fermi
pockets in the presence of fluctuating spin density wave order. We generalize
this theory to an arbitrary band structure and ordering wavevector. The
transition to the large Fermi surface state, without pockets induced by local
spin density wave order, is described by embedding the U(1) gauge theory in a
SU(2) gauge theory. The phase diagram of the SU(2) gauge theory shows that the
onset of spin density wave order in the Fermi liquid occurs either directly, in
the framework discussed by Hertz, or via intermediate non-Fermi liquid phases
with Fermi surfaces of fractionalized excitations. We discuss application of
our results to the phase diagram of the cuprates.
