Llanes Estrada, Felipe JoséDobado González, AntonioTorres Rincón, Juan Miguel2023-06-192023-06-192013-09-121550-799810.1103/PhysRevD.88.053006https://hdl.handle.net/20.500.14352/33383© 2013 American Physical Society. We thank useful conversations with T. Schaefer. This work was supported by Spanish Grants No. FPA2010-16963 and No. FPA2011-27853-C02-01. J.M.T.-R. is funded by Grant No. FP7 PEOPLE-2011-CIG under Contract No. PCIG09-GA-2011-291679.We explore the viscosities of a photon gas by means of the Euler-Heisenberg effective theory and quantum electrodynamics at zero electron chemical potential. We find parametric estimates that show a very large shear viscosity and an extremely small bulk viscosity (reflecting the very weak coupling simultaneously with a very approximate dilatation invariance). The system is of some interest because it exemplifies very neatly the influence of the breaking of scale invariance on the bulk viscosity.engjournal articlehttp://dx.doi.org/10.1103/PhysRevD.88.053006http://prd.aps.orgopen access53AstronomyAstrophysicsPhysicsParticlesFieldsFísica (Física)22 Física