Chow groups of intersections of quadrics via homological projective duality and (Jacobians of) noncommutative motives

Abstract

The Beilinson-Bloch type conjectures predict that the low degree rational Chow groups of intersections of quadrics are one dimensional. This conjecture was proved by Otwinowska. Making use of homological projective duality and the recent theory of (Jacobians of) noncommutative Chow motives, we give an alternative proof of this conjecture in the case of a complete intersection of either two quadrics or three odd-dimensional quadrics. Moreover, without the use of the powerful Lefschetz theorem, we prove that in these cases the unique non-trivial algebraic Jacobian is the middle one. As an application, making use of Vial's work, we describe the rational Chow motives of these complete intersections and show that smooth fibrations in such complete intersections over small dimensional bases S verify Murre's conjecture (dim(S) less or equal to 1), Grothendieck's standard conjectures (dim(S) less of equal to 2), and Hodge's conjecture (dim(S) less or equal to 3).