Abstract
For limiting noncompact Sobolev embeddings into continuous functions, we study the behavior of approximation, Gelfand, Kolmogorov, Bernstein and isomorphism s-numbers. In the one-dimensional case, the exact values of the above-mentioned strict s-numbers are obtained, and in the higher dimensions sharp estimates for asymptotic behavior of the strict s-numbers are established.
As all known results for s-numbers of Sobolev type embeddings are studied mainly under the compactness assumption, our work is an extension of existing results and reveal an interesting behavior of s-numbers in the limiting case when some of them (approximation, Gelfand, and Kolmogorov) have positive lower bound and others (Bernstein and isomorphism) are decreasing to zero. It also follows from our results that such limiting noncompact Sobolev embeddings are finitely strictly singular maps.