In this paper we prove the Rational Hodge Conjecture, namely that for every smooth complex projective variety X/C and every integer 0 ≤ p ≤ dimC X Hp, p (X) ∩ H2p (X, Q) = Im (cl: CHp (X) Q −→ H2p (X, Q) ). Our principal new contributions are the following four results: 1. Simultaneous validity of the standard conjectures B, C, D, I—by constructing the graph correspondence of the Lefschetz operator and the projectors ΠR, Πn, Πk as explicit Chow correspondences, we algebraically realise the Hard Lefschetz inverse map, the Künneth projectors, and the Hodge–Riemann bilinear form (the fourfold standard conjectures). 2. An algorithm for the finite generation of (p, p) Hodge classes—combining Lefschetz pencils, the spread method, and Mayer–Vietoris gluing in a five–step procedure, we show that any (p, p) class can be reduced to an algebraic cycle in finitely many steps. The computational complexity is estimated as O (ρ · deg n). 3. A unification principle via an analytic–motivic bridge—merging the standard conjectures with the generation algorithm, we establish a bridging theorem showing that the degeneracy of the Abel–Jacobi map coincides with the equality of Hodge and numerical equivalence, thereby yielding the Rational Hodge Conjecture immediately. 4. A self–contained proof system—integrating analytic L2 Hodge theory, the Lefschetz sℓ2 representation, and Chow–motivic theory, we construct a fully autonomous framework that depends on no unresolved external hypotheses. With these results, the present paper resolves the Rational Hodge Conjecture in all dimensions and degrees, while simultaneously giving a comprehensive answer to the Grothendieck programme of standard conjectures. As further applications we indicate potential extensions to the integral version, the Tate conjecture, and computer–algebraic implementations.
Y. Shimizu (Wed,) studied this question.