  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
