  The interaction of a molecule with the quantized electromagnetic field of a
nano-cavity gives rise to light-induced conical intersections between
polaritonic potential energy surfaces. We demonstrate for a realistic model of
a polyatomic molecule that the time-resolved ultrafast radiative emission of
the cavity enables to follow both nuclear wavepacket dynamics on and
nonadiabatic population transfer between polaritonic surfaces without applying
a probe pulse. The latter provides an unambiguous (and in principle
experimentally accessible) dynamical fingerprint of light-induced conical
intersections.
