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_a⁰ V_b⁰, where the V_i⁰ is a neutral vector meson produced in the forward kinematical region: s ≫ - t and - t ≫ Λ_QCD². We show how the differential cross sections dσ/dt, 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^* → q q bar , these total cross sections σ (e⁺e^- → γV⁰) and σ (e⁺e^- → V_a⁰ V_b⁰), 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.