Sharp isoperimetric inequalities on the Hamming cube near the critical exponent

TL;DR

This paper establishes new sharp isoperimetric inequalities on the Hamming cube for exponents near the critical value, improving bounds and providing tools for related conjectures and inequalities.

Contribution

It proves a new isoperimetric inequality for exponents $eta \,\geq\ 0.50057$, extending previous results, and introduces a Bellman-type function approach verified via computer-assisted proofs.

Findings

Proved isoperimetric inequality for $eta\ge 0.50057$

Achieved bounds asymptotically sharp for small subsets at $eta=0.5$

Applications to conjectures and sharp Poincaré inequalities

Abstract

An isoperimetric inequality on the Hamming cube for exponents $\beta\ge 0.50057$ is proved, achieving equality on any subcube. This was previously known for $\beta\ge \log_2(3/2)\approx 0.585$. Improved bounds are also obtained at the critical exponent $\beta=0.5$, including a bound that is asymptotically sharp for small subsets. A key ingredient is a new Bellman-type function involving the Gaussian isoperimetric profile which appears to be a good approximation of the true envelope function. Verification uses computer-assisted proofs and interval arithmetic. Applications include progress towards a conjecture of Kahn and Park as well as sharp Poincar\'e inequalities for Boolean-valued functions near $L^1$.