Diphotons, New Vacuum Angles, and Strong CP

Understand

The Standard Model contains a well-understood, natural, spin-0 diphoton resonance: the $\pi^0$.

• 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.