Extra Invariance in Time Frequency Spaces and The Amalgam Balian Low Theorem

MOLTER, URSULA

Porto Alegre

Congreso; ICM 2018 SATELLITE CONFERENCE IN HARMONIC ANALYSIS; 2018

Universidad Federal de Rio Grande do Sur

Let $\Gamma$ be a crystal group in $\R^d$. A function $\varphi:\R^d\longrightarrow \C$ is said to be {\em crystal-refinable} (or $\Gamma-$refinable) if it is a linear combination of finitely many of the rescaled and translated functions $\varphi(\gamma^{-1}(ax))$, where the {\em translations} $\gamma$ are taken on a crystal group $\Gamma$, and $a$ is an expansive dilation matrix such that $a\Gamma a^{-1}\subset\Gamma.$ A $\Gamma-$refinable function $\varphi: \R^d \rightarrow \C$ satisfies a refinement equation $\varphi(x)=\sum_{\gamma\in\Gamma}d_\gamma \varphi(\gamma^{-1}(ax))$ with $d_\gamma \in \C$. Let $\mathcal S(\varphi)$ be the linear span of $\{\varphi(\gamma^{-1}(x)): \gamma \in \Gamma\}$ and $\mathcal{S}^h=\{f(x/h):f\in\mathcal{S(\varphi)}\}$. One important property of $\mathcal S(\varphi)$ is, how well it approximates functions in $L^2(\R^d)$. This property is very closely related to the {\em crystal-accuracy} of $\mathcal S(\varphi)$, which is the highest degree $p$ such that all multivariate polynomials $q(x)$ of ${\rm degree}(q)