Probabilities of incidence between lines and a plane curve over finite fields

Mehdi Makhul, Josef Schicho, Matteo Gallet

Published 2017-11-16Version 1

We study the probability for a random line to intersect a given plane curve, defined over a finite field, in a given number of points. In particular, we focus on the limits of these probabilities under successive finite field extensions. The main tools we use are the Lang-Weil bound for the number of rational points of an algebraic variety and a geometric interpretation of the Galois group of a curve. Supposing absolute irreducibility for the curve, we prove the existence of these limits, and under a mildly stronger condition we provide an explicit formula for them, depending only on the degree of the curve.