| Résume | The Lefschetz defect of a smooth projective variety, roughly, measures the
difference between the Picard number of the variety and that of its
prime divisors. This invariant was introduced by Casagrande in 2012 and it turns out to be very useful in the classification of Fano fourfolds.
In this talk, we present a new cohomological characterization of the
Lefschetz defect. This allows us to deduce stability properties for it; in particular,
its invariance under smooth deformations of Fano manifolds.
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