The process of two-photon production of hadrons has been playing a vital role in studying the strong interaction physics during the past few decades. Since the process is essentially non-perturbative in nature, the general constraints based on analyticity and unitarity become highly important for the interpretation of the phenomenon. A new approach based on sum rules for light-by-light scattering will be presented and applications for a number of problems related to both perturbative field theory and hadronic physics will be discussed in detail.
The keen interest to the anomalous magnetic moment of muon is motivated by its high potential for probing physics beyond Standard Model. However, the interpretation of the quantity is undermined by large hadronic uncertainties. In view of the new muon (g-2) experiments at Fermilab and at J-PARC, a new dispersive formalism for evaluating the hadronic light-by-light (HLbL) scattering contribution to the muon's anomalous magnetic moment  will be presented. We provide a first realistic application of the proposed formalism to the case of pseudoscalar meson pole exchanges. Moreover, it allows for a more straightforward implementation of the experimental data. The ongoing measurements by the BES-III Collaboration will be a crucial input into the presented dispersive formalism.