We de®ne a new class of algebraic n À 1-bundles on P n , that contains the bundles introduced by Tango [14] and their stable generalized pull-backs; we show that these bundles are invariant under small deformations and that they correspond to smooth points of moduli spaces.1991 Mathematics Subject Classi®cation: 14F05.It is a very di½cult problem to ®nd examples of non-splitting algebraic vector bundles on the complex projective space P n whose rank is less than n. In particular for n 6 the only known examples are essentially the mathematical instantons [3] (for odd n) and the bundles introduced by Tango [14]: all of them have rank n À 1. Of course, pulling back the Tango bundles by a ®nite morphism P n 3 P n gives other examples of rank n À 1 bundles.In [9], Horrocks introduced a new technique of constructing new bundles from old ones, which generalizes the pull-back. This method, that we can call generalized pullback, has been extensively studied in [1] and [2] and it applies only to bundles whose symmetry group contains a copy of C Ã .In this paper we show that, for any n 3, there exists a Tango bundle that is SL2-invariant: hence the generalized pull-back allows us to de®ne a new class of n À 1-bundles on P n .More precisely, let Y g be integer numbers such that g b n 0 and let Q Y g be the bundles on P n described by the exact sequence:Q Y g can also be de®ned as the generalized pull-back of the quotient bundle on P n and, in particular, Q 0Y 1 is the quotient bundle. Let us de®ne the rank 2n À 1 vector bundle:O P n 2n À 1 À 2kXBrought to you by |