Bonn Math Events

The weakly special conjecture contradicts Orbifold Mordell, and hence abc - Special session of the HyperK seminar in Bonn on January 9 & 10, 2025

by Ariyan Javanpeykar (Nijmegen)

Europe/Berlin
Poppelsdorfer Allee 45, 1, EG, Lecture room - HIM PA82 (HIM)

Poppelsdorfer Allee 45, 1, EG, Lecture room - HIM PA82

HIM

Poppelsdorfer Allee 82 53115 Bonn
60
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Description
Abstract: Lang conjectured that varieties of general type over a number field have very few rational points. In 2000, guided by Lang's conjecture and in search of a converse statement, Abramovich, Colliot-Thelene, Harris, and Tschinkel formulated the "Weakly Special Conjecture": every weakly special variety over a number field has a potentially dense set of rational points. In this talk I will explain how this conjecture contradicts the abc conjecture, and more precisely Campana's "Orbifold Mordell" conjecture. Indeed, starting from an Enriques surface over Q(t) constructed by Lafon, we give the first examples of smooth projective weakly special threefolds which fiber over the projective line in Enriques surfaces with nowhere reduced, but non-divisible, fibers. The existence of these threefolds shows that the Weakly Special Conjecture contradicts the abc conjecture, but also shows that Enriques surfaces and K3 surfaces can have non-divisible but nowhere reduced degenerations, thereby answering a question raised by Campana in 2005. This is joint work with Finn Bartsch, Frederic Campana, and Olivier Wittenberg.
Daniel Huybrechts