Cheshire <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>θ</mml:mi></mml:math> terms, Aharonov-Bohm effects, and axions

We discuss unusual <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>θ</a:mi></a:math> terms that can appear in field theories that allow global vortices. These “Cheshire <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>θ</c:mi></c:math> terms” induce Aharonov-Bohm effects for some particles that move around vortices. For example, a Cheshire <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>θ</e:mi></e:math> term can appear in QCD coupled to an axion and induces Aharonov-Bohm effects for baryons and leptons moving around axion strings.