Rational points on certain families of symmetric equations

Abstract

We generalize the work of Dem'janenko and Silverman for the Fermat quartics, effectively determining the rational points on the curves x2m + axm + aym + y2m = b whenever the ranks of some companion hyperelliptic Jacobians are at most one. As an application, we explicitly describe Xd(ℚ) for certain d ≥ 3, where Xd : Td(x) + Td(y) = 1 and Td is the monic Chebychev polynomial of degree d. Moreover, we show how this later problem relates to orbit intersection problems in dynamics. Finally, we construct a new family of genus 3 curves which break the Hasse principle, assuming the parity conjecture, by specifying our results to quadratic twists of x4 - 4x2 - 4y2 + y4 = -6.