Timeline for Semi-continuity of the Picard number
Current License: CC BY-SA 4.0
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| 2 days ago | comment | added | Srinivasa Granujan | Dear @DoriBejleri, thanks a lot for your answer. Do you have a reference for the claim "the locus where the Picard rank jumps is a countable union of Zariski closed sets"? Thank you. | |
| Nov 5, 2022 at 23:06 | comment | added | Dori Bejleri | No, in general the locus where the Picard rank jumps is a countable union of Zariski closed sets and if we are over the complex numbers, this union can even be dense in the classical topology. This happens for example for K3 surfaces where e.g. the locus of Picard rank 2 K3s inside the moduli space of degree d K3s is a countable union over all possible rank 2 lattice polarizations. | |
| Nov 5, 2022 at 22:56 | history | asked | Puzzled | CC BY-SA 4.0 |