Anomalies and WZW-term of two-flavour QCD

The U(2)_R x U(2)_L symmetry of QCD with two massless flavours is subject to anomalies which affect correlation functions involving the singlet currents A^0_\mu or V^0_\mu. These are relevant for pion-photon interactions, because - for two flavours - the electromagnetic current contains a singlet piece. We give the effective Lagrangian required for the corresponding low energy analysis to next-to-leading order, without invoking an expansion in the mass of the strange quark. In particular, the Wess-Zumino-Witten term that accounts for the two-flavour anomalies within the effective theory is written down in closed form.