  A spin-charge unifying description for the Hubbard model based on the time
dependent local gauge transformations is developed. The collective variables
for charge and spin are isolated in the form of the space-time fluctuating U(1)
phase field and rotating spin quantization axis governed by the SU(2) symmetry,
respectively. As a result interacting electrons appear as a composite objects
consisting of bare fermions with attached U(1) and SU(2) gauge fields. We
elaborate on the microscopic origins of the effective action with the Coulomb
interaction that contain topological theta terms. Furthermore, we unravel the
link between non-trivial multiply-connected topological structure of the
U(2)=U(1)$\otimes$SU(2) configurational space for gauge fields and the
instanton contribution to the statistical sum.
