Powers of Symmetric Differential Operators I

Let $L$ be a linear symmetric differential operators on $L^{2}\left( \mathbb{R}\right)$ whose domain is the Schwartz test function space, $\mathcal{S}.$ For the majority of this paper, it is assumed that the coefficient of $L$ are polynomial functions on $\mathbb{R}.$ We will give criteria on the polynomial coefficients of $L$ which guarantees that $L$ is essentially self-adjoint, $\bar{L}\geq-CI$ for some $C<\infty,$ and that $\mathcal{S}$ is a core for $\left( \bar{L}+C\right) ^{r}$ for all $r\geq0.$ Given another polynomial coefficient differential operator, $\tilde{L},$ we will further give criteria on the coefficients $L$ and $\tilde{L}$ which implies operator comparison inequalities of the form $\left( \overline {\tilde{L}}+\tilde{C}\right) ^{r}\leq C_{r}\left( \bar{L}+C\right) ^{r}$ for all $0\leq r<\infty.$ The last inequality generalized to allow for an added parameter, $\hbar>0,$ in the coefficients is used to provide a large class of operators satisfying the hypotheses in our another paper "On the classical limit of quantum mechanics" (will be submitted very soon) where a strong form of the classical limit of quantum mechanics is shown to hold.