An Improved Dictatorship Test with Perfect Completeness

A Boolean function f : {0, 1} → {0, 1} is called a dictator if it depends on exactly one variable i.e f(x1, x2, . . . , xn) = xi for some i ∈ [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 perfect completeness if it accepts any dictator function. The 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 2k+1 2k , where k is of the form 2 − 1 for any integer t > 2. This improves upon the result of [TY15] which gave a dictatorship test with soundness 2k+3 2k .