Direct photon production in relativistic heavy-ion collisions -- a theory update

For tomographic studies of relativistic nuclear collisions and of the quark-gluon plasma, photons (real and virtual) are unique. They are the only probes than can be both soft and penetrating. First we report on advances in modelling the hadron dynamics of heavy-ion collisions using a hybrid approach which consists of IP-Glasma, relativistic fluid dynamics, and hadronic cascade components. We briefly discuss the “photon flow puzzle”, and then focus on a recent development in the theory of photon emission from a non-equilibrium, strongly interacting medium.