We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC. Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics. Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their pT -differential anisotropic flow coefficients vn(pT ) are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. Viscous corrections to the rates are found to have a larger effect on the vn coefficients than the viscous suppression of hydrodynamic flow anisotropies. The benefits of taking the ratio of elliptic to triangular flow, v2/v3, are discussed, and the spacetime regions which contribute dominantly to the photon flow harmonics are identified. The directed flow v1 of thermal photons is predicted for RHIC and LHC energies.

We perform 3+1D viscous hydrodynamics calculations of proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our goal is to understand the apparent collective behavior recently observed in pA collisions and to verify whether the highest multiplicity collision systems can be accurately described as a relativistic fluid. We compare our calculations of flow variables to existing measurements, and demonstrate that hydrodynamics correctly captures the measured trends. We show that our predictions for the pair correlation observable r n are validated by recent experimental pA measurements, and that our results are sensitive to the granularity of the initial state. We also compare our results with measurements done for nucleus-nucleus collisions.

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