An Improved Dictatorship Test with Perfect Completeness

Abstract

A Boolean function $f:\{0,1{\}}^n\to \{0,1\}$ is called a dictator if it depends on exactly one variable i.e $f(x_1,x_2,\dots ,x_n)=x_i$ for some $i\in [n]$. In this work, we study a $k$-query dictatorship test. Dictatorship tests are central in proving many hardness results for constraint satisfaction problems. The dictatorship test is said to have {\em perfect completeness} if it accepts any dictator function. The {\em soundness} of a test is the maximum probability with which it accepts any function far from a dictator. Our main result is a $k$-query dictatorship test with perfect completeness and soundness $\frac{2k+1}{2^k}$, where $k$ is of the form $2^t-1$ for any integer $t>2$. This improves upon the result of \cite{TY15} which gave a dictatorship test with soundness $\frac{2k+3}{2^k}$.

21 pages