Published online by Cambridge University Press: 21 May 2019
We prove that, for any finite set $A\subset \mathbb{Q}$ with
$|AA|\leqslant K|A|$ and any positive integer
$k$, the
$k$-fold product set of the shift
$A+1$ satisfies the bound
$$\begin{eqnarray}|\{(a_{1}+1)(a_{2}+1)\cdots (a_{k}+1):a_{i}\in A\}|\geqslant \frac{|A|^{k}}{(8k^{4})^{kK}}.\end{eqnarray}$$
$K$ is of the order
$c\log |A|$, for a sufficiently small constant
$c=c(k)$. Our main tool is a multiplicative variant of the
$\unicode[STIX]{x1D6EC}$-constants used in harmonic analysis, applied to Dirichlet polynomials.