# Balian-Low type theorems on homogeneous groups

## TL;DR

This paper establishes strict density conditions for coherent frames and Riesz sequences on homogeneous groups, extending Balian-Low type theorems to a broad class of nilpotent Lie groups.

## Contribution

It proves necessary density inequalities for frames and Riesz sequences on homogeneous groups, generalizing classical results to a wider mathematical setting.

## Key findings

- Density of frames must be strictly greater than the formal dimension.
- Density of Riesz sequences must be strictly less than the formal dimension.
- The results rely on deformation theorems and analysis on homogeneous groups.

## Abstract

We prove strict necessary density conditions for coherent frames and Riesz sequences on homogeneous groups. Let $N$ be a connected, simply connected nilpotent Lie group with a dilation structure (a homogeneous group) and let $(\pi, \mathcal{H}_{\pi})$ be an irreducible, square-integrable representation modulo the center $Z(N)$ of $N$ on a Hilbert space $\mathcal{H}_{\pi}$ of formal dimension $d_\pi $. If $g \in \mathcal{H}_{\pi}$ is an integrable vector and the set $\{ \pi (\lambda )g : \lambda \in \Lambda \}$ for a discrete subset $\Lambda \subseteq N / Z(N)$ forms a frame for $\mathcal{H}_{\pi}$, then its density satisfies the strict inequality $D^-(\Lambda )> d_\pi $, where $D^-(\Lambda )$ is the lower Beurling density. An analogous density condition $D^+(\Lambda) < d_{\pi}$ holds for a Riesz sequence in $\mathcal{H}_{\pi}$ contained in the orbit of $(\pi, \mathcal{H}_{\pi})$. The proof is based on a deformation theorem for coherent systems, a universality result for $p$-frames and $p$-Riesz sequences, some results from Banach space theory, and tools from the analysis on homogeneous groups.