Spectrum of the Laplacian on a complete Riemannian manifold with nonnegative Ricci curvature which possess a pole (Q1342808)

Let \(\sigma_{\text{ess}}\) denote the essential spectrum of the Laplacian on functions. The author proves that if \(M\) is a complete noncompact Riemannian manifold with nonnegative Ricci curvature and if \(M\) possesses a pole, then \(\sigma_{\text{ess}}(\Delta) = [0,\infty)\). This result generalizes previous work by \textit{J. F. Escobar} and \textit{A. Freire} [Duke Math. J. 65, No. 1, 1-21 (1992; Zbl 0764.53028)].