Diphotons, new vacuum angles, and strong CP

The standard model contains a well-understood, natural, spin-0 diphoton resonance: the π 0. numerous studies have pointed out that the hint of a new diphoton resonance at 750 gev could be a pion analog, identified with the pseudo-nambu-goldstone boson of a chiral symmetry spontaneously broken by new strong dynamics at the tev scale. these “hypercolor” models are generically expected to violate parity through a topological angle $$ tilde{theta} $$ . we discuss the physics of $$ tilde{theta} $$ and its impact on the phenomenology of the new sector. we also describe some of the theoretical implications of a nonzero $$ tilde{theta} $$ . in particular, $$ tilde{theta} $$ can generate an $$ mathcal{o}(1) $$ threshold correction to the qcd vacuum angle θ near the tev scale, sharply constraining ultraviolet solutions to the strong cp problem. alternatively, finding that $$ tilde{theta} $$ is small be interpreted as evidence in favor of uv solutions to strong cp, particularly those based on spontaneously broken p or cp symmetries.