Charm diffusion in a pion gas implementing unitarity, chiral and heavy quark symmetries

► We compute charm drag and diffusion in a pion gas (in heavy ion collisions). ► We employ effective theory (both chiral and heavy quark). ► We unitarize the perturbative amplitude for realistic cross-sections. ► A charm quark with momentum 1 GeV loses 50 MeV per fermi (drag). ► The momentum distribution broadens some 100 MeV per fermi (diffusion).