On the Riemann zeta-function and the divisor problem
  Let $\Delta(x)$ denote the error term in the Dirichlet divisor problem, and $E(T)$ the error term in the asymptotic formula for the mean square of $|\zeta(1/2 + it)|$. If $E^*(t) = E(t) - 2\pi\Delta^*(t/(2\pi))$ with $\Delta^*(x) = - \Delta(x) +2\Delta(2x)- {1\over2}\Delta(4x)$, then we obtain $$ \int_0^T(E^*(t))^4 dt \ll_\epsilon T^{16/19+varepsilon}$$, which is the first non-trivial bound for higher moments of $E^*(t)$. The method of proof also provides an upper bound for sums of fourth powers of mean square integrals of $|\zeta(1/2 + it)|$ over well-spaced points. This, in turn, yields a new proof of the twelfth moment estimate for $|\zeta(1/2 + it)|$. Among the chief ingredients in the proof is a recent result of Robert--Sargos on the distribution of four square roots of integers, plus an approach of M. Jutila that involves the use of Airy integrals to deal with the ensuing exponential sums. 
Aleksandar Ivi\'c