Diphotons, New Vacuum Angles, and Strong CP

Abstract

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. 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 $\theta$ near the TeV scale, sharply constraining ultraviolet solutions to the strong CP problem. Alternatively, finding that $\tilde{\theta }$ is small may be interpreted as evidence in favor of UV solutions to strong CP, particularly those based on spontaneously broken P or CP symmetries.

23 pages, 6 figures. v2: references added, fig 1 updated

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Cited by in corpus (15)

• Interpreting the 750 GeV digamma excess: a review
• Left-right asymmetry and 750 GeV diphoton excess
• Models of LHC Diphoton Excesses Valid up to the Planck scale
• Theta in new QCD-like sectors
• Indirect Signs of the Peccei-Quinn Mechanism
• Color-octet Companions of a 750 GeV Heavy Pion
• Diphotons from an Electroweak Triplet-Singlet
• Composite Dark Matter with Forbidden Annihilation
• Learning from the New Higgs-like Scalar before It Vanishes
• Minimal Dilaton Model and the Diphoton Excess
• 750 GeV Diphotons from Supersymmetry with Dirac Gauginos
• Peccei-Quinn Symmetry Breaking via Asymptotically Safe Dynamical Scalegenesis: A Walking Axicolor and Axion
• Superbumps
• Implications of perturbative unitarity for scalar di-boson resonance searches at LHC
• Uncovering an Axion Mechanism with the EDM Portfolio