Coercivity of weighted Kohn Laplacians: the case of model monomial weights in $\mathbb{C}^2$

Abstract

The weighted Kohn Laplacian $\Box_\varphi$ is a natural second order elliptic operator associated to a weight $\varphi:\mathbb{C}^n\rightarrow\mathbb{R}$ and acting on $(0,1)$-forms, which plays a key role in several questions of complex analysis. We consider here the case of model monomial weights in $\mathbb{C}^2$, i.e., $ \varphi(z,w):=\sum_{(\alpha,\beta)\in\Gamma}|z^\alpha w^\beta|^2, $ where $\Gamma\subseteq \mathbb{N}^2$ is finite. Our goal is to prove coercivity estimates of the form $\Box_\varphi\geq \mu^2$, where $\mu:\mathbb{C}^n\rightarrow\mathbb{R}$ acts by pointwise multiplication on $(0,1)$-forms, and the inequality is in the sense of self-adjoint operators. We recently proved (arxiv.org:1502.00865) how to derive from $\mu$-coercivity estimates for $\Box_\varphi$ pointwise bounds for the weighted Bergman kernel associated to $\varphi$. Here we introduce a technique to establish $\mu$-coercivity with $ \mu(z,w)=c(1+|z|^a+|w|^b) \qquad(a,b\geq0),$ where $a,b\geq0$ depend (and are easily computable from) $\Gamma$. As a corollary we also prove that, for a wide class of model monomial weights, the spectrum of $\Box_\varphi$ is discrete if and only if the weight is not decoupled, i.e. $\Gamma$ contains at least a point $(\alpha,\beta)$ with $\alpha\neq0\neq\beta$. Our methods comprise a new holomorphic uncertainty principle and linear optimization arguments.