Addition Formulae for Non-Abelian Theta Functions and Applications
  This paper generalizes for non-abelian theta functions a number of formulae valid for theta functions of Jacobian varieties. The addition formula, the relation with the Szego kernel and with the multicomponent KP hierarchy and the behavior under cyclic coverings are given. 
E. G\'omez Gonz\'alez and F. J. Plaza Mart\'in