Process gamma* gamma -> sigma at large virtuality of gamma*
  The process gamma* gamma -> sigma is investigated in the framework of the SU(2)xSU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of gamma* in the Euclidean kinematic domain. The asymptotic behaviour of this form factor resembles the asymptotic behaviour of the gamma* gamma -> pi form factor. 
M. K. Volkov, A. E. Radzhabov, V. L. Yudichev