A Topological Criterion for Alice Strings

Abstract

Symmetry breaking can produce ``Alice'' strings, which alter scattered charges and carry monopole number and charge when twisted into loops. Alice behavior arises algebraically, when a string's untraced Wilson loop obstructs unbroken symmetries -- a fragile criterion. We give a topological criterion, compelling Alice behavior or deforming it away. Our criterion, that \pi_o(H) acts nontrivially on \pi_1(H), links topologically Alice strings to topological monopoles. We twist Alice loops to form monopoles, and find nematic and He-3A Alice strings are topologically Alice, carrying fundamental monopole charge when twisted into loops.