Trying to Understand the lower bound on the Schrodinger Operator of the Hydrogen atom. Using the kato-rellich theorem. My education has been in physics and i am slowly adding to my mathematics toolset.I am yet to study fuctional analysis exrensively the following problem is in my way to understanding the following theorem.
Could someone explain this to me.
For refrence This is a step in theorem 9.38 Quantum Theory for Mathematicians. Authors: Brian C. Hall. Series Title: Graduate Texts in Mathematics. DOI: https://doi.org/10.1007/978-1-4614-7116-5.
Given that $$ \mathbf{DOM}(\Delta) = \{ \psi \in \mathbf{L^2}(\mathbb{R^n})\space | \space |\mathbf{k^2}\hat{\psi}(k) \in \mathbf{L^2}(\mathbb{R^n}) \} $$
Define $ \Delta $ as
$$\Delta \psi = -\pmb{F^{-1}}(\mathbf{k^2}\hat{\psi}(\mathbf(k) ) $$
Show that for any $\epsilon \gt 0 $ there exists a constant $C_{\epsilon} $ such that $$ \lvert \psi \rvert \leq {C_\epsilon} \lVert \psi \rVert + \epsilon\lVert \Delta\psi \rVert $$