QCD vacuum structure in strong magnetic fields
We study the response of the QCD vacuum to strong magnetic fields, using a potential model for the quark-antiquark interaction. We find that production of spin-polarized u-ubar pairs is energetically favorable for fields B > B_crit \sim 10 GeV^2. We contrast the resulting u-ubar condensate with the quark condensate which is present at zero magnetic field, and we estimate the corresponding magnetization as a function of B.