On the p^(λ) problem

We deal with the distribution of the fractional parts of $p^{\lambda}$, $p$ running over the prime numbers and $\lambda$ being a fixed real number lying in the interval $(0,1)$. Roughly speaking, we study the following question: Given a real $\theta$, how small may $\delta>0$ be choosen if we suppose that the number of primes $p\le N$ satisfying ${p^{\lambda}-\theta<\delta}$ is close to the expected one? We improve some results of Balog and Harman on this question for $\lambda<5/66$ if $\theta$ is rational and for $\lambda<1/5$ if $\theta$ is irrational. Our improvement is based on incorporating the zero detection argument into Harman's method and on using new mean value estimates for products of shifted and ordinary (unshifted) Dirichlet polynomials.