Polynomial bounds for the Chowla Cosine Problem

Benjamin Bedert

Let $A\subset \mathbf{N}$ be a finite set of $n=|A|$ positive integers, and consider the cosine sum $f_A(x)={\sum }_{a\in A}\cos ax$. We prove that $$\min_x f_A(x)\leqslant -n^{ 1/5-o…