# On product of difference sets for sets of positive density

## TL;DR

This paper proves that for two positive density subsets of integers, their difference sets' product contains a scaled integer subgroup, with bounds depending only on the densities, extending to modular settings.

## Contribution

It establishes a bound on the product of difference sets for positive density sets and derives a modular analogue with uniform bounds depending only on densities.

## Key findings

- Existence of a bounded integer multiple contained in the product of difference sets.
- Extension of the main result to modular arithmetic with uniform bounds.
- Provides a structural insight into difference sets of positive density subsets.

## Abstract

In this paper we prove that given two sets $E_1,E_2 \subset \mathbb{Z}$ of positive density, there exists $k \geq 1$ which is bounded by a number depending only on the densities of $E_1$ and $E_2$ such that $k\mathbb{Z} \subset (E_1-E_1)\cdot(E_2-E_2)$. As a corollary of the main theorem we deduce that if $\alpha,\beta > 0$ then there exist $N_0$ and $d_0$ which depend only on $\alpha$ and $\beta$ such that for every $N \geq N_0$ and $E_1,E_2 \subset \mathbb{Z}_N$ with $|E_1| \geq \alpha N, |E_2| \geq \beta N$ there exists $d \leq d_0$ a divisor of $N$ satisfying $d \, \mathbb{Z}_N \subset (E_1-E_1)\cdot(E_2-E_2)$.