Computability of the essential spectrum of differential forms

Let $(M^n,g)$ be a complete noncompact Riemannian manifold with asymptotically nonnegative Ricci curvature. For $0\leq k\leq n$, write $\sigma_{\rm ess}(k,\Delta,M)$ for the essential spectrum of the Laplacian on $k$-forms on $M$. Computability conjecture. For each $k$, either

$$\sigma_{\rm ess}(k,\Delta,M)=\emptyset$$

or

$$\sigma_{\rm ess}(k,\Delta,M)=[a_k,\infty)$$

for some $a_k\geq 0$. This would give a precise description of the essential spectrum under asymptotically nonnegative Ricci curvature, whereas the preceding results establish the full half-line in certain degrees but do not settle the general case.