  We study the thermal and electric transport of a fluid of interacting Dirac
fermions using a Boltzmann approach. We include Coulomb interactions, a dilute
density of charged impurities and the presence of a magnetic field to describe
both the static and the low frequency response as a function of temperature T
and chemical potential mu. In the quantum-critical regime mu << T we find
pronounced deviations from Fermi liquid behavior, such as a collective
cyclotron resonance with an intrinsic, collision-broadened width, and
significant enhancements of the Mott and Wiedemann-Franz ratio. Some of these
results have been anticipated by a relativistic hydrodynamic theory, whose
precise range of validity and failure at large fields and frequencies we
determine. The Boltzmann approach allows us to go beyond the hydrodynamic
regime, and to quantitatively describe the deviations from
magnetohydrodynamics, the crossover to disorder dominated Fermi liquid behavior
at large doping and low temperatures, as well as the crossover to the ballistic
regime at high fields. Finally, we obtain the full frequency and doping
dependence of the single universal conductivity sigma_Q which parametrizes the
hydrodynamic response.
