Electromagnetic response of dense quark matter around color-superconducting phase transition and QCD critical point

We explore how the electric conductivity and associated relaxation time are modified near the QCD critical point and the phase transition to a color superconducting phase using the two-flavor Nambu–Jona–Lasinio model with finite current quark masses. We give a comprehensive account of the nature of the soft modes associated with these phase transitions and how they affect the photon self-energy when the system approaches these phase transitions in a combined way with an emphasis on the common and different aspects in the two transitions. The formalism developed for describing the paraconductivity in metallic superconductors is used for the analysis of the photon self-energy. We show that the transport coefficients calculated from the self-energy show anomalous enhancements in both cases with different critical exponents for the individual transitions. We briefly discuss the possibility of detecting the enhancements in the relativistic heavy-ion collisions in the present and future facilities.