5-field terms in the open superstring effective action
  Some time ago the bosonic and fermionic 4-field terms of the non-abelian low energy effective action of the open superstring were obtained, to all order in $\alpha'$. This was done at tree level by directly generalizing the abelian case, treated some time before, and considering the known expressions of all massless superstring 4-point amplitudes (at tree level). In the present work we obtain the bosonic 5-field terms of this effective action, to all order in $\alpha'$. This is done by considering the simplified expression of the superstring 5-point amplitude for massless bosons, obtained some time ago. 
Luiz Antonio Barreiro and Ricardo Medina