Photon emission from strongly magnetized QCD plasma

By making use of an explicit Landau-level representation for the imaginary part of the photon polarization tensor, the direct photon emission from a strongly magnetized quark-gluon plasma is calculated. The leading order contribution comes from the three processes of the zeroth order in the coupling constant $\alpha_s$: (i) the quark splitting ($q\rightarrow q+\gamma $), (ii) the antiquark splitting ($\bar{q} \rightarrow \bar{q}+\gamma $), and (iii) the quark-antiquark annihilation ($q + \bar{q}\rightarrow \gamma$). It is found that the Landau-level quantization leads to a nontrivial momentum dependence of the photon ellipticity coefficient $v_2$, which takes negative values at small transverse momenta and positive values at large transverse momenta. The crossover between the two regimes occurs around $k_T\simeq \sqrt{|eB|}$. The nonisotropic photon emission may explain in part a large positive value of $v_2$ for the direct photons produced in ultrarelativistic heavy-ion collisions.