Pure Spinor Formalism for Osp(N|4) backgrounds
  We start from the Maurer-Cartan (MC) equations of the Osp(N|4) superalgebras satisfied by the left-invariant super-forms realized on supercoset manifolds of the corresponding supergroups and we derive some new pure spinor constraints. They are obtained by "ghostifying" the MC forms and extending the differential d to a BRST differential. From the superalgebras G =Osp(N|4) we single out different subalgebras H contained in G associated with the different cosets G/H: each choice of H leads to a different weakening of the pure spinor constraints. In each case, the number of parameter is counted and we show that in the cases of Osp(6|4)/U(3) x SO(1,3), Osp(4|4)/SO(3) x SO(1,3) and finally Osp(4|4) U(2)} x SO(1,3) the bosonic and fermionic degrees of freedom match in order to provide a c=0 superconformal field theory. We construct both the Green-Schwarz and the pure spinor sigma model for the case Osp(6|4)/U(3)x SO(1,3) corresponding to AdS_4 x P^3. The pure spinor sigma model can be consistently quantized. 
Pietro Fr\'e and Pietro Antonio Grassi