Field-strength correlators for QCD in a magnetic background
  We present the results of an exploratory study (by means of Monte Carlo simulations on the lattice) of the properties of the gauge-invariant two-point correlation functions of the gauge-field strengths for $N_f=2$ QCD at zero temperature and in the presence of a magnetic background field: the analysis provides evidence for the emergence of anisotropies in the nonperturbative part of the correlators and for an increase of the gluon condensate as a function of the external magnetic field. 
Enrico Meggiolaro, Massimo D'Elia, Michele Mesiti, Francesco Negro
hep-lat hep-ph hep-th