How exotic symmetries survive the journey from M-theory to string theory

Compactifying M-theory on a circle down to Type IIA supergravity is a well-worn path, but how its more exotic symmetries — defects that cannot be inverted like ordinary group elements — survive that descent is not obvious. The authors track the full non-invertible defect structure, including auxiliary topological sectors, through the Kaluza-Klein reduction. A seven-dimensional Chern-Simons-like theory collapses to a six-dimensional BF-type sector, while the Bianchi identity splits the symmetries into an ordinary invertible piece and a twisted non-invertible piece tied together by the Type IIA flux relation. The charged objects on each side are matched through the standard M-theory/Type IIA brane dictionary.