The maximal probability that k-wise independent bits are all 1

A k-wise independent distribution on n bits is a joint distribution of the bits such that each k of them are independent. In this paper we consider k-wise independent distributions with identical marginals, each bit has probability p to be 1. We address the following question: how high can the probability that all the bits are 1 be, for such a distribution? For a wide range of the parameters n, k and p we find an explicit lower bound for this probability which matches an upper bound given by Benjamini et al., up to multiplicative factors of lower order. The question we investigate can be seen as a relaxation of a major open problem in error-correcting codes theory, namely, how large can a linear error correcting code with given parameters be? The question is a type of discrete moment problem, and our approach is based on showing that bounds obtained from the theory of the classical moment problem provide good approximations for it. The main tool we use is a bound controlling the change in the expectation of a polynomial after small perturbation of its zeros. [email protected]. Department of Statistics, UC Berkeley. Supported by Microsoft Research and NSF grant DMS-0605166. [email protected]. Department of Mathematics, The Weizmann Institute of Science, Rehovot, 76100 Israel. [email protected]. Department of Computer Science and Applied Mathematics, The Weizmann Institute of Science, Rehovot, 76100 Israel. Research supported by a grant from the Israel Ministry of Science (IMOS) Eshkol Fellowship.