Enhanced thermal photon and dilepton production in strongly coupled N=4 SYM plasma in strong magnetic field

Abstract

We calculate the DC conductivity tensor of strongly coupled N=4 super-Yang-Mills (SYM) plasma in a presence of a strong external magnetic field B>>T^2 by using its gravity dual and employing both the RG flow approach and membrane paradigm which give the same results. We find that, since the magnetic field B induces anisotropy in the plasma, different components of the DC conductivity tensor have different magnitudes depending on whether its components are in the direction of the magnetic field B. In particular, we find that a component of the DC conductivity tensor in the direction of the magnetic field B increases linearly with B while the other components (which are not in the direction of the magnetic field B) are independent of it. These results are consistent with the lattice computations of the DC conductivity tensor of the QCD plasma in an external magnetic field B. Using the DC conductivity tensor, we calculate the soft or low-frequency thermal photon and dilepton production rates of the strongly coupled N=4 SYM plasma in the presence of the strong external magnetic field B>>T^2. We find that the strong magnetic field B enhances both the thermal photon and dilepton production rates of the strongly coupled N=4 SYM plasma in a qualitative agreement with the experimentally observed enhancements at the heavy-ion collision experiments.