Abstract
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 may be interpreted as evidence in favor of UV solutions to strong CP, particularly those based on spontaneously broken P or CP symmetries.
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Draper, P., McKeen, D. Diphotons, new vacuum angles, and strong CP. J. High Energ. Phys. 2016, 127 (2016). https://doi.org/10.1007/JHEP04(2016)127
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DOI: https://doi.org/10.1007/JHEP04(2016)127