  We propose one possible mechanism for an anomalous metallic phase appearing
frequently in two spatial dimensions, that is, local pairing fluctuations.
Introducing a pair-rotor representation to decompose bare electrons into
collective pairing excitations and renormalized electrons, we derive an SU(2)
gauge theory of the Hubbard model as an extended version of its U(1) gauge
theory\cite{Florens,LeeLee} to allow only local density fluctuations. Since our
effective SU(2) gauge theory admits two kinds of collective bosons
corresponding to pair excitations and density fluctuations respectively, an
intermediate phase appears naturally between the spin liquid Mott insulator and
Fermi liquid metal of the U(1) gauge theory,\cite{Florens,LeeLee} characterized
by softening of density-fluctuation modes as the Fermi liquid, but gapping of
pair-excitation modes. We show that this intermediate phase is identified with
an anomalous metallic phase because there are no electron-like quasiparticles
although it is metallic.
