Product Mixing in Compact Lie Groups
Electron. Colloquium Comput. Complex.(2024)
摘要
If G is a group, we say a subset S of G is product-free if the equation
xy=z has no solutions with x,y,z ∈ S. For D ∈ℕ, a group G
is said to be D-quasirandom if the minimal dimension of a nontrivial complex
irreducible representation of G is at least D. Gowers showed that in a
D-quasirandom finite group G, the maximal size of a product-free set is at
most |G|/D^1/3. This disproved a longstanding conjecture of Babai and Sós
from 1985.
For the special unitary group, G=SU(n), Gowers observed that his argument
yields an upper bound of n^-1/3 on the measure of a measurable product-free
subset. In this paper, we improve Gowers' upper bound to exp(-cn^1/3),
where c>0 is an absolute constant. In fact, we establish something stronger,
namely, product-mixing for measurable subsets of SU(n) with measure at least
exp(-cn^1/3); for this product-mixing result, the n^1/3 in the
exponent is sharp.
Our approach involves introducing novel hypercontractive inequalities, which
imply that the non-Abelian Fourier spectrum of the indicator function of a
small set concentrates on high-dimensional irreducible representations.
Our hypercontractive inequalities are obtained via methods from
representation theory, harmonic analysis, random matrix theory and differential
geometry. We generalize our hypercontractive inequalities from SU(n) to an
arbitrary D-quasirandom compact connected Lie group for D at least an
absolute constant, thereby extending our results on product-free sets to such
groups.
We also demonstrate various other applications of our inequalities to
geometry (viz., non-Abelian Brunn-Minkowski type inequalities), mixing times,
and the theory of growth in compact Lie groups.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要