arXiv subjects
Publications and source records attributed to Ben Johnsrude.
We study nonlinear H\"older--Brascamp--Lieb inequalities over $\mathbb{Z}^n$. Our method embeds the integers into a suitable compactification, over which local H\"older--Brascamp--Lieb theory may be applied (e.g heat flow). Our main result is a bound for multilinear H\"older--Brascamp--Lieb functionals over suitable sublattices in $\mathbb{Z}^n$.
We demonstrate two applications of Fourier decoupling theorems over non-Archimedean local fields to real-variable problems. These include short mean value estimates for exponential sums, canonical-scale mean value estimates for exponential sums arising from phase functions with coefficients arising from the traces of powers of algebraic numbers, and solution counting bounds for Vinogradov systems whose indeterminates are families of algebraic numbers. We also record an example where real and $\mathfrak p$-adic decoupling estimates differ.
We prove a small cap decoupling theorem for the parabola over a general non-Archimedean local field for which $2\neq 0$. We obtain polylogarithmic dependence on the scale parameter $R$ and polynomial dependence in the residue prime, except for the prime 2 for which the polynomial depends on degree. Our constants are fully explicit.
We prove a restricted projection theorem for Borel subsets of $\mathbb{Q}_p^n$ in the regime $p>n$. This generalizes results of Gan-Guo-Wang in the real setting. Our result is effective in the sense that explicit constants are obtained for various covering numbers. Along the way, we prove a fully explicit Fourier decoupling theorem for the moment curve in $p$-adic Cartesian space.
We note that the subpolynomial factor for the $\ell^qL^p$ small cap decoupling constants for the truncated parabola $\mathbb{P}^1=\{(t,t^2):|t|\leq 1\}$ may be controlled by a suitable power of $\log R$. This is achieved by considering a suitable amplitude-dependent wave envelope estimate, as was introduced in a recent paper of Guth and Maldague to demonstrate a small cap decoupling for the $(2+1)$ cone; we demonstrate that the version for $\mathbb{P}^1$ may be taken with a loss controlled by a power of $\log R$ as well.