Integral points on quadrics with prime coordinates

Let f (x ₁, . . . , x _s ) be a regular indefinite integral quadratic form, and t an integer. Denote by V the affine quadric {x : f (x) = t}, and by V(\mathbb P){V(\mathbb {P})} the set of x ? V{{\bf x}\in V} whose coordinates are simultaneously prime. It is proved that, under suitable conditions, V(\mathbbP){V(\mathbb{P})} is Zariski dense in V as long as s ≥ 10.