Thomas Ransford

collaborators

3 papers

math.CA2026

A functional inequality related to Domar's uniform boundedness theorem

Thomas Ransford

We study the functional inequality \[ f(r+s)\le g(r)+Î±f(s) \quad(r,s>0). \] Here $g : (0, \infty) \to [0, \infty)$ is a given decreasing function, $I^\pm$ is a constant such that $0 < I^\pm < 1$ ,…

math.FA2026

A proof of Esterle's conjecture on negative powers of Hilbert-space contractions

Thomas Ransford

We establish the following result, confirming a conjecture of Jean Esterle. For each closed subset $E$ of the unit circle of Lebesgue measure zero, there exists a positive sequence…

math.FA2024

Contractivity of MÃ¶bius functions of operators

Thomas Ransford, Dashdondog Tsedenbayar

Let $T$ be a injective bounded linear operator on a complex Hilbert space. We characterize the complex numbers $I^», I^¼$ for which $(I + I^» T) (I + I^¼ T)^{- 1}$ is a contraction, the charact…