Power Residue Criteria for Quadratic Units and the Negative Pell Equation

Abstract

AbstractLet d > 1 be a square-free integer. Power residue criteria for the fundamental unit εd of the real quadratic fields modulo a prime p (for certain d and p) are proved by means of class field theory. These results will then be interpreted as criteria for the solvability of the negative Pell equation x2 − dp2y2 = −1. The most important solvability criterion deals with all d for which has an elementary abelian 2-class group and p ≡ 5 (mod 8) or p ≡ 9 (mod 16).