From ABC to Effective Roth and Ridout Constants for Cubic Roots

Abstract

Enrico Bombieri showed conditionally (1994) that the ABC conjecture implies Roth's theorem, and Van Frankenhuysen (1999) later provided a complete proof. Building on Bombieri's and Van der Poorten's explicit formula for continued-fraction coefficients of algebraic numbers (specialized to cubic roots) we derive an effective bound for a Roth-type constant assuming an effective form of ABC. Roth's original argument establishes existence but does not yield an explicit value; our approach makes the dependence on the ABC parameters explicit and also gives an explicit bound in the corresponding special case of Ridout's theorem. We then introduce the notion of approximation gain as a refinement of the quality of an abc-triple. For c in a large computational range, the approximation gain remains below a strikingly small threshold, motivating the conjecture that the approximation gain is always smaller than 1.5. This suggests a potential strategy for attacking ABC by bounding approximation gain and power gain separately.