  Polaritons - hybrid light-matter states formed in cavity - strongly change
the properties of the underlying matter. In optical or plasmonic nanocavities,
polaritons decay by radiative emission of the cavity, which is accessible
experimentally. Due to the interaction of a molecule with the quantized
radiation field, polaritons exhibit light-induced conical intersections (LICIs)
which dramatically influence the nuclear dynamics of molecular polaritons. We
show that ultrafast radiative emission from the lower polariton is controlled
by the geometric phase imposed by the LICI. This finding provides insight into
the process of emission and, furthermore, allows one to compute these signals
by augmenting the Born-Oppenheimer approximation for polaritons with a
geometric phase term.
