Eigenfunction expansions associated with 1d periodic differential operators of order $2n$

V. Tkachenko

We prove an explicit formula for the spectral expansions in $L^2(\mathbb{R})$ generated by selfadjoint differential operators $$ (-1)^n\frac{d^{2n}}{dx^{2n}}+\sum\limits_{j=0}^{n-1}\frac{d…