Growth beyond exponent $3/2$ for convexity and iterated sum sets

Abstract

We prove that the bound \[ \max \{ |16A|,|16f(A)| \} \gg_m |A|^{\frac{3}{2}+\frac{1}{162}} \] holds for any polynomial $f$ with degree $m\ge 2$ and any finite $A\subset \mathbb{R}$. This shows that the classical Jarník obstruction to growth beyond exponent $3/2$, which occurs for general strictly convex functions, cannot occur for polynomial functions.