Effective bounds for the negativity of Shimura curves on Hilbert modular surfaces

Abstract

The Bounded Negativity Conjecture states that for each smooth projective surface X defined over a field of characteristic zero there exists a number b(X) bigger or equal to 0 such that the self-intersection number C^2 for every reduced, irreducible curve C in X is bounded below by b(X), i.e. C^2 is bigger or equal to -b(X). In this thesis, we consider Hirzebruch-Zagier curves on Hilbert modular surfaces and give explicit bounds for the self-intersection numbers in these cases. More general, we give a bound for the self-intersection number of reduced, irreducible Shimura curves C on Hilbert modular surfaces X, generalising a result from the literature from compact Hilbert modular surfaces to non-compact Hilbert modular surfaces. We compare the resulting bounds with the actual self-intersection numbers of Hirzebruch-Zagier curves calculated with Pari/GP.