  We analyze the Large Hadron Collider sensitivity to new pseudoscalar
resonances decaying into diphoton with masses up to scales of few TeVs. We
focus on minimal scenarios where the production mechanisms involve either
photon or top-mediated gluon fusion, partially motivated by the tantalizing
excess around 750 GeV reported by ATLAS and CMS. The two scenarios lead
respectively to a narrow and a wide resonance. We first provide a
model-independent analysis via effective operators and then introduce minimal
models of composite dynamics where the diphoton channel is characterized by
their topological sector. The relevant state here is the pseudoscalar
associated with the axial anomaly of the new composite dynamics. If the
Standard Model top mass is generated via four-fermion operators the coupling of
this state to the top remarkably explains the wide-width resonance reported by
ATLAS. Beyond the excess, our analysis paves the way to test dynamical
electroweak symmetry breaking via topological sectors.
