Quantum loops in radiative decays of the a1 and b1 axial-vector mesons

A previous model where the low-lying axial-vector mesons are dynamically generated, implementing unitarity in coupled channels in the vector-pseudoscalar (VP) meson interaction, is applied to evaluate the decay widths of the a1(1260) and b1(1235) axial-vector mesons into πγ. Unlike the case of the a1, the b1 radiative decay is systematically underestimated at tree level. In this work we evaluate for the first time the loop contribution coming from an initial VP vertex. Despite the large superficial divergence of the loops, the convergence of the relevant loops can be established by using arguments of gauge invariance. The partial decay widths obtained agree with the experimental values within uncertainties, and we show that the loop contribution is crucial in the b1 case and also important for the a1 case.