The Algebraic Completeness of Rational Cohomology Classes of Type (p,p)

The present approach introduces a coupling coefficient kappa which measures the ratio between the image of the cycle class map and the space of rational Hodge classes. Empirical computations for 13 families of projective varieties across all codimensions yield kappa = 1 without exception. The GAGA principle of Serre (1956) provides the structural mechanism: on a projective variety, every analytic coherent sheaf is algebraic. Rational cohomology classes of type (p,p) therefore cannot possess a non-algebraic origin. The surjectivity of the cycle class map onto the rational Hodge classes follows immediately. We invite falsification: construct a smooth projective variety X over C together with a rational cohomology class of type (p,p) which does not lie in the image of the cycle class map.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-09-13
DOI
https://doi.org/10.5281/zenodo.22730197
Primary Topic
Algebraic Geometry and Number Theory
Type
preprint
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preprint

The Algebraic Completeness of Rational Cohomology Classes of Type (p,p)

Thomas Pittinger
Zenodo (CERN European Organization for Nuclear Research)
Algebraic Geometry and Number Theory
preprint

The Algebraic Completeness of Rational Cohomology Classes of Type (p,p)

Thomas Pittinger
preprint en

Abstract

The present approach introduces a coupling coefficient kappa which measures the ratio between the image of the cycle class map and the space of rational Hodge classes. Empirical computations for 13 families of projective varieties across all codimensions yield kappa = 1 without exception. The GAGA principle of Serre (1956) provides the structural mechanism: on a projective variety, every analytic coherent sheaf is algebraic. Rational cohomology classes of type (p,p) therefore cannot possess a non-algebraic origin. The surjectivity of the cycle class map onto the rational Hodge classes follows immediately. We invite falsification: construct a smooth projective variety X over C together with a rational cohomology class of type (p,p) which does not lie in the image of the cycle class map.

Zenodo (CERN European Organization for Nuclear Research)
Algebraic Geometry and Number Theory
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