1989, Journal of the London Mathematical Society
Many variations of the theorems of Dirichlet and Kronecker in Diophantine approximation [3, Chapters 11.3 and 23] have been established, by restricting the class of integers allowed in the problem. For example, see [1], where one is restricted to the values taken by a polynomial with integer coefficients. Another example is afforded by the following theorem. Suppose that a is irrational and let \\y\\ denote the smallest distance of y from an integer. Then, for any real number ft, there are infinitely many primes p such that \\ap-p\\<p-3 ' 10. (1.1) This result was established in [5], improving earlier results of Vinogradov [11, Chapter 11] and Vaughan [9]. In this paper we shall consider extending this result to simultaneous approximation. In [4, Chapter 3] the author considered this problem for sets of not very well approximable numbers (see [7], or below for the definition) and this paper develops the author's previously unpublished work. Balog and Friedlander have recently done some work on this question [2], but our results supersede theirs in all cases. We wish to prove that max is ' small' for infinitely many primes p. A necessary restriction on a 15 ..., OL S is given by the following definition due to Balog and Friedlander. A set of real numbers {a l5 ..., a s } is called compatible if s s £ «, a, e Q implies that ^^a^e Z whenever n lt ...n s are integers. Balog and Friedlander then proved the following. Let {a 15 ..., a s } be a compatible set of real algebraic numbers, lying in a field of degree d. Then, for any A < (3ds + d-s-\)~1, there are infinitely many solutions in primes p to max || pa, || <p~A. We improve this result as follows.