Quark condensate in a magnetic field

We study the dependence of quark condensate Σ on an external magnetic field. For weak fields, it rises linearly: Σ(H) = Σ(0) [1 + eHln2(16π2Fπ2) + …]. Mπ and Fπ are also shifted so that the Gell-Mann-Oakes-Renner relation is satisfied. In the strong field region, Σ(H) α (eH)32.