A Tauberian Approach to an Analog of Weyl's law for the Kohn Laplacian on Compact Heisenberg Manifolds

Let $M=\mathrm{\Gamma }\setminus {\mathbb{H}}_d$ be a compact quotient of the $d$-dimensional Heisenberg group ${\mathbb{H}}_d$ by a lattice subgroup $\mathrm{\Gamma }$. We show that the eigenvalue counting function $N(\lambda )$ for any fixed element of a family of second order differential operators $\left\{{\mathcal{L}}_{\alpha }\right\}$ on $M$ has asymptotic behavior $N\left(\lambda\right) \sim C_{d,\alpha} \operatorname{vol}\left(M\right) \lambda^{d + 1}$,where$C_{d,\alpha}$ is a constant that only depends on the dimension $d$ and the parameter $\alpha$. As a consequence, we obtain an analog of Weyl’s law (both on functions and forms) for the Kohn Laplacian on $M$. Our main tools are Folland’s description of the spectrum of ${\mathcal{L}}_{\alpha }$ and Karamata’s Tauberian theorem.