Boojums in SuperfluidHe3-Aand Cholesteric Liquid Crystals

Because of the similarity of their order parameters, there are close analogies between defects of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$ and cholesteric liquid crystals. In particular, boojums, originally predicted for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$A$, should exist as well in cholesterics. Certain textures experimentally observed and reported in the literature are identified as boojums. A topological analysis is given, and the effects of boojums on dynamical properties of cholesterics are discussed.