Harmonic maps and shift-invariant subspaces
With the help of operator-theoretic methods, we derive new and powerful criteria for finiteness of the uniton number for a harmonic map from a Riemann surface to the unitary group U(n). These use the Grassmannian model where harmonic maps are represented by families of shift-invariant subspaces of L2(S1, Cn) ; we give a new description of that model.