Possible mixing between elementary and bound state fields in the $$t\bar{t}$$ t t ¯ production excess at the LHC

Abstract Recent report by CMS Collaboration on the excess of top and anti-top pair production is studied, under the hypothesis of the coexistence of a toponium $$(\eta _t)$$ ( η t ) and an additional elementary field $$(\Psi )$$ ( Ψ ) . We examine the scenario where toponium and an additional field are mixed, and consider the plausible scenarios in that case. Two scenarios are examined: one is the minimal model with $$\Psi $$ Ψ close to the inert Higgs doublet, and the other is embedded into the two Higgs doublet models (2HDM), where $$\Psi $$ Ψ is one of the two Higgs scalars after transforming the basis. The value of each coupling constant is restricted by the Multicritical Point Principle (MPP). Consistency with the data gives constraints on a mixing angle $$\theta \ (-45^\circ \le \theta \le 45^\circ )$$ θ ( - 45 ∘ ≤ θ ≤ 45 ∘ ) , with which the mass eigenstate $$\Psi ^\prime $$ Ψ ′ contributing to the excess is defined by $$\Psi ^\prime =\Psi \cos \theta + \eta _t\sin \theta $$ Ψ ′ = Ψ cos θ + η t sin θ . The obtained results are $$|\theta | \le 13^{\circ }$$ | θ | ≤ 13 ∘ for the minimum scenario, and $$|\theta | \le 1^{\circ }$$ | θ | ≤ 1 ∘ for the second scenario of 2HDM (Type II and Y). We also briefly discuss the comparison with Type I and X.