Monopole, half-quantum vortex, and nexus in chiral superfluids and superconductors

Two exotic objects are still not identified experimentally in chiral superf luids and superconductors. These are the half-quantum vortex, which plays t he part of the Alice string in relativistic theories [A. S. Schwarz, Nucl. Phys. B 208, 141 (1982)], and the hedgehog in the l field, which is the cou nterpart of the Dirac magnetic monopole. These two objects of different dim ensionality are topologically connected. They form a combined object which is called a nexus [John M. Cornwall, hep-th/9911125; Phys. Rev. D 59, 12501 5 (1999); Phys. Rev. D 58, 105028 (1998)] or center monopole [N. N. Chernod ub, M. I. Polikarpov, A. I. Veselov and M. A. Zubkov, Nucl. Phys. Proc. Sup pl. 73, 575 (1999)] in relativistic theories. Such a combination will permi t the observation of half-quantum vortices and monopoles in several realist ic geometries. (C) 1999 American Institute of Physics. [S0021-3640(99)00224 -8].