Magnetic test of chiral dynamics in QCD

Strong magnetic fields in the range eB≫m_π² effectively probe internal quark structure of chiral mesons and test basic parameters of the chiral theory, such as 〈q-barq〉,f_π. We argue on general grounds that 〈q-barq〉 should grow linearly with eB when charged quark degrees of freedom come into play. To make explicit estimates we extend the previously formulated chiral theory, including quark degrees of freedom, to the case of strong magnetic fields and show that the quark condensate |〈q-barq〉|_u,d grows quadratically with eB for eB<0.2 GeV² and linearly for higher field values. These results agree quantitatively with recent lattice data and differ from χPT predictions