On inhomogeneous extension of Thue-Roth's type inequality with moving targets

Abstract

Let $\Gamma\subset \overline{\mathbb Q}^{\times}$ be a finitely generated multiplicative group of algebraic numbers. Let $\delta, \beta\in\overline{\mathbb Q}^\times$ be algebraic numbers with $\beta$ irrational. In this paper, we prove that there exist only finitely many triples $(u, q, p)\in\Gamma\times\mathbb{Z}^2$ with $d = [\mathbb{Q}(u):\mathbb{Q}]$ such that $$ 0<|\delta qu+\beta-p|<\frac{1}{H^\varepsilon(u)q^{d+\varepsilon}}, $$ where $H(u)$ denotes the absolute Weil height. As an application of this result, we also prove a transcendence result, which states as follows: Let $\alpha>1$ be a real number. Let $\beta$ be an algebraic irrational and $\lambda$ be a non-zero real algebraic number. For a given real number $\varepsilon >0$, if there are infinitely many natural numbers $n$ for which $||\lambda\alpha^n+\beta|| < 2^{- \varepsilon n}$ holds true, then $\alpha$ is transcendental, where $||x||$ denotes the distance from its nearest integer. When $\alpha$ and $\beta$ both are algebraic satisfying same conditions, then a particular result of Kulkarni, Mavraki and Nguyen, proved in [3] asserts that $\alpha^d$ is a Pisot number. When $\beta $ is algebraic irrational, our result implies that no algebraic number $\alpha$ satisfies the inequality for infinitely many natural numbers $n$. Also, our result strengthens a result of Wagner and Ziegler [6]. The proof of our results uses the Subspace Theorem based on the idea of Corvaja and Zannier [2] together with various modification play a crucial role in the proof.