## Schedule

##### 11:00-11:50 Background on higher-order Fourier analysis (Arnab Bhattacharyya, IISc )

This talk is a mathematical primer for the rest of the workshop. I define the basic notions that form the foundations of higher-order Fourier analysis over finite fields, such as bias, Gowers norm and polynomial rank. I will discuss the interrelationships between these notions, regularity lemmas and show proofs of mini-results to illustrate the theorems.

##### 11:55-12:35 Regularity of polynomials and linear forms (Pooya Hatami, U. Chicago)

Higher-order Fourier analysis is a strong tool in the study of analytic averages involving linear structures. One examines such averages by replacing the involved functions by their Higher-order Fourier expansion and reducing the problem to studying averages involving bounded degree polynomials. However for this representation to be useful, one often needs nice distributional/pseudorandomness properties of the involved polynomials such as approximate orthogonality or almost independence.

We will talk about regularity of polynomials which was introduced by Green-Tao and Kauffman-Lovett in order to provide such approximate orthogonalities. In most applications, however, one requires stronger regularity properties of the polynomials. We will overview the proof of such a strong near-orthogonality over arbitrary systems of linear forms, and show as an application that this can be used to settle a conjecture of Gowers and Wolf regarding the true complexity of systems of linear forms.

The talk is based on a joint work with Hamed Hatami and Shachar Lovett.

##### 14:00-14:40 Algorithmic higher-order Fourier analysis (Madhur Tulsiani, TTIC)

Decomposition theorems proved by Gowers and Wolf provide an appropriate notion of "Fourier transform" for higher-order Fourier analysis. We will discuss some questions and techniques that arise from trying to develop polynomial time algorithms for computing these decompositions.

The original proofs for these theorems were non-constructive and used the Hahn-Banach theorem. We will discuss constructive proofs based on boosting which reduce the problem of computing these decompositions to a certain kind of weak decoding for codes beyond the list-decoding radius. We will also describe some special cases for which such decodings are known to be possible, and the techniques which achieve these.

Based on joint works with Arnab Bhattacharyya, Eli Ben-Sasson, Pooya Hatami, Noga Ron-Zewi and Julia Wolf.

##### 14:50-15:30 Applications to algebraic property testing (Yuichi Yoshida, NII)

Property testing aims for constant-query algorithms that distinguish objects satisfying a predetermined property from objects that are “far” from satisfying it. Along with the development of the higher order Fourier analysis, there has been rapid progress in testing affine-invariant properties of functions over a finite field, including low-degree polynomials, and finally a characterization of affine-invariant properties that are testable with a constant number of queries was achieved. In this talk, we survey these results.

##### 16:00-16:40 Applications to coding theory (Abhishek Bhowmick, UT Austin)

The list decoding problem for a code asks for the maximal radius up to which any ball of that radius contains only a constant number of codewords. The list decoding radius is not well understood even for well studied codes, like Reed-Solomon or Reed-Muller codes. The Reed-Muller code for a finite field is defined by n-variate degree-d polynomials over . As far as we know, the list decoding radius of Reed- Muller codes can be as large as the minimal distance of the code. This is known in a number of cases: The Goldreich-Levin theorem and its extensions established it for d = 1 (Hadamard codes); Gopalan, Klivans and Zuckerman established it for the binary field ; and Gopalan established it for d = 2 and all fields. In a recent work with Lovett, we prove the conjecture for all constant prime fields and all constant degrees. The proof relies on several new ingredients, including higher-order Fourier analysis.

Based on joint work with Shachar Lovett.

##### 16:50-17:30 Interleaved products in special linear groups: mixing and communication complexity (Emanuele Viola, Northeastern)

Let S and T be two dense subsets of Gn, where G is the special linear group SL(2,p) for a prime p congruent to 3 modulo 4. If you sample uniformly a tuple (s1,...,sn) from S and a tuple (t1,...,tn) from T then their interleaved product s1.t1.s2.t2...sn.tn is equal to any fixed g in G with probability (1 + |G|-Ω(n))/|G|.

Equivalently, the communication complexity of distinguishing tuples whose interleaved product is equal to g from those whose product is equal to a different g' is Ω(n log |G|), even if the protocol is randomized and only achieves a small advantage over random guessing. This result is tight and improves on the Ω(n) bound that follows by reduction from the inner product function.

Gowers (2007) and later Babai, Nikolov, and Pyber proved that if S, T, and U are dense subsets of a simple, non-abelian group G, then STU = g with probability (1/|G|)(1 + o(1)). For the special case of G = SL(2,p), this also follows from our result. Unlike previous proofs, ours does not rely on representation theory.

Joint work with Timothy Gowers.