On the eigenvectors of the 5D discrete Fourier transform number operator in Newtonian basis
Natig Atakishiyev
TL;DR
This work develops an analytic framework to compute the eigenvalues and eigenvectors of the 5D discrete number operator $\mathcal{N}_5 = A_5^{\intercal} A_5$ by exploiting the $P_d$-symmetry of the intertwining operators with respect to the 5-point DFT $\Phi_5$. It constructs an explicit ladder of eigenvectors $f_0,\dots,f_4$ with corresponding eigenvalues and shows $\mathcal{N}_5$ commutes with $\Phi_5$, thus classifying $\Phi_5$'s eigenvectors and resolving degeneracies. A sparsealization procedure isolates symmetric/antisymmetric annihilators, enabling a discrete analog of the continuous harmonic-oscillator formulas, notably expressing $f_n$ as $f_n = d_n^{-1}\mathcal{P}_n(X_5) f_0$ where $\mathcal{P}_n$ are Newtonian-basis polynomials. The paper links the discrete framework to an Askey-Wilson/Cubic-algebra structure and provides a concrete, algebraic method for spectral analysis of the 5-point DFT with potential numerical applications.
Abstract
A simple analytic approach to the evaluation of the eigenvalues and eigenvectors f_n of the 5D discrete number operator N_5 is formulated. This approach is essentially based on the symmetry of the intertwining operators with respect to the discrete reflection operator. A procedure for the sparsealization of the intertwining operators has been developed, which made it possible to establish a discrete analog of the well-known continuous case formula. A discrete analog for the eigenvectors f_n of another continuous case formula is constructed in the Newtonian basis polynomials, times the lowest eigenvector f_0.
