Abstract:
Let X be the product of a smooth
projective curve C and a smooth projective surface S over a
field K. Assume the Chow group of zero-cycles on S is just Z
over any algebraically closed field extension of F (example :
Enriques surface). For K the complex field, one may give
counterexamples to the integral Hodge conjecture for 1-cycles
(Benoist-Ottem) on X and this may be understood from the point of
view of unramified cohomology. For K a finite field, in joint work
with Federico Scavia (UBC, Vancouver) we give a simple condition on
C and S which ensures that the integral Tate conjecture holds
for 1-cycles on X. An equivalent formulation is a vanishing result
for unramified cohomology of degree 3.