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A SMALL VALUE ESTIMATE FOR $\mathbb {G}_{{\textrm{a}}}\times \mathbb {G}_{{\textrm{m}}}$

Part of: Diophantine approximation, transcendental number theory

Published online by Cambridge University Press:  01 February 2013

Damien Roy
Damien Roy*
Affiliation:
Department of Mathematics and Statistics, University of Ottawa, 585 King Edward, Ottawa K1N 6N5, Canada (email: droy@uottawa.ca)
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Abstract

A small value estimate is a statement providing necessary conditions for the existence of certain sequences of non-zero polynomials with integer coefficients taking small values at points of an algebraic group. Such statements are desirable for applications to transcendental number theory to analyze the outcome of the construction of an auxiliary function. In this paper, we present a result of this type for the product $ \mathbb {G}_{\mathrm {a}}\times \mathbb {G}_{\mathrm {m}}$ whose underlying group of complex points is $\mathbb {C}\times \mathbb {C}^{*}$. It shows that if a certain sequence of non-zero polynomials in $ \mathbb {Z}[X_1,X_2]$ takes small values at a point $(\xi ,\eta )$ together with their first derivatives with respect to the invariant derivation $\partial /\partial X_1 + X_2 (\partial /\partial X_2)$, then both $\xi $ and $\eta $ are algebraic over $\mathbb {Q}$. The precise statement involves growth conditions on the degree and norm of these polynomials as well as on the absolute values of their derivatives. It improves on a direct application of Philippon’s criterion for algebraic independence and compares favorably with constructions coming from Dirichlet’s box principle.

MSC classification

Secondary: 11J85: Algebraic independence; Gel'fond's method 11J81: Transcendence (general theory)
Type
Research Article
Information
Mathematika , Volume 59 , Issue 2 , July 2013 , pp. 333 - 363
Copyright
Copyright © 2013 University College London 

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