Number Theory Seminar

Julie Desjardins, University of Toronto Mississauga

"Torsion points and concurrent exceptional curves on del Pezzo surfaces of degree one"

The blow up of the anticanonical base point on X, a del Pezzo surface of degree 1, gives rise to a rational elliptic surface E with only irreducible fibers. The sections of minimal height of E are in correspondence with the 240 exceptional curves on X. A natural question arises when studying the configuration of those curves : 

If a point of X is contained in « many » exceptional curves, it is torsion on its fiber on E?

In 2005, Kuwata proved for del Pezzo surfaces of degree 2 (where there is 56 exceptional curves) that if « many » equals 4 or more, then yes. With Rosa Winter, we prove that for del Pezzo surfaces of degree 1, if « many » equals 9 or more, then yes, but we find counterexamples where a torsion point lies at the intersection lies at the intersection of 7 exceptional curves.

This seminar will be held jointly online and in person:

• Room: MC 5479
• Zoom information: https://uwaterloo.zoom.us/j/99239659097?pwd=ZjNVRjQ1MWpuQmhTb01ZS0RGNDJjQT09