Spin polarization of half-quantum vortex in systems with equal spin pairing.

We present a variational analysis for a half-quantum vortex (HQV) in the equal-spin-pairing superfluid state which, under suitable conditions, is believed to be realized in Sr(2)RuO(4) and (3)He-A. Our approach is based on a description of the HQV in terms of a BCS-like wave function with a spin-dependent boost. We predict a novel feature: the HQV, if stable, should be accompanied by a nonzero spin polarization. Such a spin polarization would exist in addition to the one induced by the Zeeman coupling to the external field and hence may serve as an indicator in experimental search for HQV.