Take the 2-minute tour ×
MathOverflow is a question and answer site for professional mathematicians. It's 100% free, no registration required.

Lang conjectured that for an irrational algebraic number $\alpha$ and $\epsilon > 0$, there exist only finitely may rationals $p/q$ such that $$ \left| \alpha - \frac{p}{q} \right| <\frac{1}{q^2(\ln q)^{1+\epsilon}} \ .$$ Presumably the heuristic here rests on the observation that the set of all reals that violate this condition has measure zero (which follows because a certain sum of characteristic functions has a finite integral). But this applies equally to $$ \left| \alpha - \frac{p}{q} \right| <\frac{1}{q^2\ln q (\ln \ln q)^{1+\epsilon}}$$ and $$ \left| \alpha - \frac{p}{q} \right| <\frac{1}{q^2\ln q \ln \ln q (\ln \ln \ln q )^{1+\epsilon}},$$ etc.

So, my questions:

1) Do these strengthenings of Roth's theorem/Lang's conjecture appear in the literature? If not, is it because

a) there's no pragmatic point in considering them until someone settles Lang's conjecture or

b) there's some theoretical or known reason actually to doubt their truth.

2) The heuristic above for Lang's conjecture fails if we take $\epsilon=0$, but I don't know where one looks for counter-examples - meaning algebraic numbers (with deg>2) with infinitely many rational approximations that satisfy for some $c$ $$ \left| \alpha - \frac{p}{q} \right| <\frac{c}{q^2\ln q}$$ or if such do exist, then analogous statements with more iterated logarithms in the denominator on the right.

share|improve this question
To be true, nothing is known towards any of your (and Lang's) questions, although there are some false achievements on this way (for example, Tasoev, B. G. On a conjecture of S. Lang. (Russian) Vladikavkaz. Mat. Zh. 4 (2002), no. 2, vmj.ru/articles/2002_2_11.zip -- be aware that the proof there is wrong). –  Wadim Zudilin Jan 24 '12 at 11:47

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.