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 $T\neq 0$, $\mu_q \neq 0$, and $H\neq 0$ have been obtained and the low-energy theorems have been derived. Bulk viscosity $\zeta(T, \mu, H)$ has been described in terms of the main thermodynamic quantities characterizing the quark-gluon matter at $T\neq 0$, $\mu_q \neq 0$, and $H\neq 0$. Various limiting cases have been discussed.