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Thermal photon $v_2$ with slow quark chemical equilibration

Elliptic flow of direct photons in high-energy heavy ion collisions has been a topic of great interest as it is experimentally found larger than most hydrodynamic expectations. I discuss the implication of possible late formation of quark component in the hot QCD medium on the photon elliptic flow as quarks are the source of thermal photons in the deconfined phase. Hydrodynamic equations are numerically solved with the evolution equations for quark and gluon number densities. The numerical results suggest that thermal photon $v_2$ is visibly enhanced by the slow chemical equilibration of quarks and gluons, reducing the aforementioned problem.