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Register a new userAn asymmetric bound for sum of distance sets
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For $ Esubset mathbb{F}_q^d$, let $Delta(E)$ denote the distance set determined by pairs of points in $E$. By using additive energies of sets on a paraboloid, Koh, Pham, Shen, and Vinh (2020) proved that if $E,Fsubset mathbb{F}_q^d $ are subsets with $|E||F|gg q^{d+frac{1}{3}}$ then $|Delta(E)+Delta(F)|> q/2$. They also proved that the threshold $q^{d+frac{1}{3}}$ is sharp when $|E|=|F|$. In this paper, we provide an improvement of this result in the unbalanced case, which is essentially sharp in odd dimensions. The most important tool in our proofs is an optimal $L^2$ restriction theorem for the sphere of zero radius.
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Let $K$ be a totally real number field of degree $n geq 2$. The inverse different of $K$ gives rise to a lattice in $mathbb{R}^n$. We prove that the space of Schwartz Fourier eigenfunctions on $mathbb{R}^n$ which vanish on the component-wise square root of this lattice, is infinite dimensional. The Fourier non-uniqueness set thus obtained is a discrete subset of the union of all spheres $sqrt{m}S^{n-1}$ for integers $m geq 0$ and, as $m rightarrow infty$, there are $sim c_{K} m^{n-1}$ many points on the $m$-th sphere for some explicit constant $c_{K}$, proportional to the square root of the discriminant of $K$. This contrasts a recent Fourier uniqueness result by Stoller. Using a different construction involving the codifferent of $K$, we prove an analogue of our results for discrete subsets of ellipsoids. In special cases, these sets also lie on spheres with more densely spaced radii, but with fewer points on each. We also study a related question about existence of Fourier interpolation formulas with nodes $sqrt{Lambda}$ for general lattices $Lambda subset mathbb{R}^n$. Using results about lattices in Lie groups of higher rank, we prove that, if $n geq 2$ and if a certain group $Gamma_{Lambda} leq operatorname{PSL}_2(mathbb{R})^n$ is discrete, then such interpolation formulas cannot exist. Motivated by these more general considerations, we revisit the case of one radial variable and prove, for all $n geq 5$ and all real $lambda > 2$, Fourier interpolation results for sequences of spheres $sqrt{2 m/ lambda}S^{n-1}$, where $m$ ranges over any fixed cofinite set of non-negative integers. The proof relies on a series of Poincare type for Hecke groups of infinite covolume, similarly to the construction previously used by Stoller.
Any bounded tile of the field $mathbb{Q}_p$ of $p$-adic numbers is a compact open set up to a zero Haar measure set. In this note, we give a simple and direct proof of this fact.
We consider sets of positive integers containing no sum of two elements in the set and also no product of two elements. We show that the upper density of such a set is strictly smaller than 1/2 and that this is best possible. Further, we also find the maximal order for the density of such sets that are also periodic modulo some positive integer.
Let $G$ be a finite (not necessarily abelian) group and let $p=p(G)$ be the smallest prime number dividing $|G|$. We prove that $d(G)leq frac{|G|}{p}+9p^2-10p$, where $d(G)$ denotes the small Davenport constant of $G$ which is defined as the maximal integer $ell$ such that there is a sequence over $G$ of length $ell$ contains no nonempty one-product subsequence.
We prove a conjecture of the first-named author ([J14]) on the upper bound Fourier coefficients of automorphic forms in Arthur packets of split classical groups over any number field.
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