Static solitons with nonzero Hopf number

We investigate a generalized nonlinear O(3) sigma model in three space dimensions where the fields are maps from R-3 boolean OR{infinity} to S-2. Such maps are classified by a homotopy invariant called the Hopf number which takes integer values. The model exhibits soliton solutions of closed vortex type which have a lower topological bound on their energies. We numerically compute the fields for topological charge 1 and 2 and discuss their shapes and binding energies. The effect of an additional potential term is considered and an approximation is given for the spectrum of slowly rotating solitons. [S0556-2821(97)00520-1].