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

Abstract

The nonperturbative QCD vacuum at finite temperature and a finite baryon density in an external magnetic field is studied. Equations relating nonperturbative condensates to the thermodynamic pressure for $T\ne 0$, ${\mu }_q\ne 0$ and $H\ne 0$ are obtained, and low-energy theorems are derived. A bulk viscosity $\zeta (T,\mu ,H)$ is expressed in terms of basic thermodynamical quantities describing the quark-gluon matter at $T\ne 0$, ${\mu }_q\ne 0$, and $H\ne 0$. Various limiting cases are also considered.

Comments: 12 pages; v2: title changed, new section about bulk viscosity and new references added; v3: new discussion added