Low-energy theorems of QCD and bulk viscosity at finite temperature and baryon density in a magnetic field

The nonperturbative QCD vacuum at finite temperature and baryon density in an external magnetic field has been studied. Relations between the nonperturbative condensates and the thermodynamic pressure at T ≠ 0, μ _q ≠ 0, and H ≠ 0 have been obtained and the low-energy theorems have been derived. Bulk viscosity ζ(T, μ, H) has been described in terms of the main thermodynamic quantities characterizing the quark-gluon matter at T ≠ 0, μq ≠ 0, and H ≠ 0. Various limiting cases have been discussed.