Decoupling, exponential sums and the Riemann zeta function

We establish a new decoupling inequality for curves in the spirit of [B-D1], [B-D2] which implies a new mean value theorem for certain exponential sums crucial to the Bombieri-Iwaniec method as developed further in [H]. In particular, this leads to an improved bound $|\zeta(\frac 12+it)|\ll t^{53/342+\varepsilon}$ for the zeta function on the critical line