Given an alphabet size m ∈ N thought of as a constant, and k = (k 1 , . . . , k m ) whose entries sum of up n, the k-multi-slice is the set of vectors x ∈ [m] n in which each symbol i ∈ [m] appears precisely k i times. We show an invariance principle for low-degree functions over the multi-slice, to functions over the product space ([m] n , µ n ) in which µ(i) = k i /n. This answers a question raised by [22].As applications of the invariance principle, we show:1. An analogue of the "dictatorship test implies computational hardness" paradigm for problems with perfect completeness, for a certain class of dictatorship tests. Our computational hardness is proved assuming a recent strengthening of the Unique-Games Conjecture, called the Rich 2-to-1 Games Conjecture.Using this analogue, we show that assuming the Rich 2-to-1 Games Conjecture, (a) there is an r-ary CSP P r for which it is NP-hard to distinguish satisfiable instances of the CSP and instances that are at most 2r+1 2 r + o(1) satisfiable, and (b) hardness of distinguishing 3-colorable graphs, and graphs that do not contain an independent set of size o(1).
A reduction of the problem of studying expectations of products of functions on the multi-slice tostudying expectations of products of functions on correlated, product spaces. In particular, we are able to deduce analogues of the Gaussian bounds from [40] for the multi-slice.3. In a companion paper, we show further applications of our invariance principle in extremal combinatorics, and more specifically to proving removal lemmas of a wide family of hypergraphs H called ζ-forests, which is a natural extension of the well-studied case of matchings.