Roth's theorem, Lang's conjecture and beyond

2011-03-24T21:13:25Z

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.

Roth's theorem, Lang's conjecture and beyond - MathOverflow

Roth's theorem, Lang's conjecture and beyond