Abstract:
We prove an explicit formula for spectral expansions in $L^2(\mathbb{R})$ generated by self-adjoint differential operators
$$
(-1)^n\frac{d^{2n}}{dx^{2n}}+\sum_{j=0}^{n-1}\frac{d^{j}}{dx^{j}}\,
p_j(x)\frac{d^{j}}{dx^{j}}\,,\qquad p_j(x+\pi)=p_j(x),\quad x\in\mathbb{R}.
$$