The γ∗γ∗→ ηc (1S; 2S) transition form factor from quarkonium wave functions
We discuss γ ∗γ ∗→ ηc(1S) ; ηc (2S) transition form factor for both virtual photons. The general formula is given. We use difierent models for the cc̄ wave function obtained from the solution of the Schrödinger equation for diffierent cc̄ potentials: harmonic oscillator, Cornell, logarithmic, power-law, Coulomb and Buchmüller{Tye. We showed some examples of wave functions in the Light Front repres