3 papers
math.FA2026
Spectral decomposition of doubly power-bounded elements in Banach algebras
Osamu Hatori, Shiho Oi
We establish a characterization of doubly power-bounded elements with finite spectrum in Banach algebras. In particular, we present a spectral decomposition for such elements, exte…
math.FA2026
Spectrally additive maps on the positive cones of the Wiener algebra
Shiho Oi, Kaito Sato
We study surjective maps between the positive cones of the Wiener algebra that preserve the spectrum of the sum of every two elements. We show that such maps can be extended to iso…
math.FA2025
Spectral decomposition of power-bounded operators: The finite spectrum case
Shiho Oi, Jyamira Oppekepenguin
In this paper, we investigate power-bounded operators, including surjective isometries, on Banach spaces. Koehler and Rosenthal asserted that an isolated point in the spectrum of a…