QCD compositeness as revealed in exclusive vector boson reactions through double-photon annihilation: e⁺e⁻ → γγ^⁎ → γV⁰ and e⁺e⁻ → γ^⁎γ^⁎ → V⁰V⁰

We study the exclusive double-photon annihilation processes, e⁺e⁻→γγ^⁎→γV⁰ and e⁺e⁻→γ^⁎γ^⁎→V_a ⁰V_b ⁰, where the V_i ⁰ is a neutral vector meson produced in the forward kinematical region: s≫−t and −t≫Λ_QCD ². We show how the differential cross sections dσdt, as predicted by QCD, have additional falloff in the momentum transfer squared t due to the QCD compositeness of the hadrons, consistent with the leading-twist fixed-θ_CM scaling laws, both in terms of conventional Feynman diagrams and by using the AdS/QCD holographic model to obtain the results more transparently. However, even though they are exclusive channels and not associated with the conventional electron–positron annihilation process e⁺e⁻→γ^⁎→qq¯, these total cross sections σ(e⁺e⁻→γV⁰) and σ(e⁺e⁻→V_a ⁰V_b ⁰), integrated over the dominant forward- and backward-θ_CM angular domains, scale as 1/s, and thus contribute to the leading-twist scaling behavior of the ratio R_e⁺e⁻ . We generalize these results to exclusive double-electroweak vector-boson annihilation processes accompanied by the forward production of hadrons, such as e⁺e⁻→Z⁰V⁰ and e⁺e⁻→W⁻ρ⁺. These results can also be applied to the exclusive production of exotic hadrons such as tetraquarks, where the cross-section scaling behavior can reveal their multiquark nature.