Sandra Mary Thampi | Searcharxiv

arXiv2025

Gohberg-Krupnik Localisation for Discrete Wiener-Hopf Operators on Orlicz Sequence Spaces

Let $Φ$ be an $N$-function whose Matuszewska-Orlicz indices satisfy $1<α_Φ\leβ_Φ<\infty$. Using these indices, we introduce ``interpolation friendly" classes of Fourier multipliers $M_{[Φ]}$ and $M_{\langleΦ\rangle}$ such that $M_{[Φ]}\subset M_{\langleΦ\rangle}\subset M_Φ$, where $M_Φ$ is the Banach algebra of all Fourier multipliers on the reflexive Orlicz sequence space $\ell^Φ(\mathbb{Z})$. Applying the Gohberg-Krupnik localisation in the corresponding Calkin algebra, the study of Fredholmness of the discrete Wiener-Hopf operator $T(a)$ with $a\in M_{\langleΦ\rangle}$ is reduced to that of $T(a_τ)$ for certain, potentially easier to study, local representatives $a_τ\in M_{[Φ]}$ of $a$ at all points $τ\in[-π,π)$.

math.FA↗

arXiv2025

On multiplier analogues of the algebra $C+H^\infty$ on weighted rearrangement-invariant sequence spaces

Let $X(\mathbb{Z})$ be a reflexive rearrangement-invariant Banach sequence space with nontrivial Boyd indices $α_X,β_X$ and let $w$ be a symmetric weight in the intersection of the Muckenhoupt classes $A_{1/α_X}(\mathbb{Z})$ and $A_{1/β_X}(\mathbb{Z})$. Let $M_{X(\mathbb{Z},w)}$ denote the collection of all periodic distributions $a$ generating bounded Laurent operators $L(a)$ on the space $X(\mathbb{Z},w)=\{φ:\mathbb{Z}\to\mathbb{C}:φw\in X(\mathbb{Z})\}$. We show that $M_{X(\mathbb{Z},w)}$ is a Banach algebra. Further, we consider the closure of trigonometric polynomials in $M_{X(\mathbb{Z},w)}$ denoted by $C_{X(\mathbb{Z},w)}$ and $H_{X(\mathbb{Z},w)}^{\infty,\pm}= \{a\in M_{X(\mathbb{Z},w)}:\widehat{a}(\pm n)=0 \mbox{ for }n<0\}$. We prove that $C_{X(\mathbb{Z},w)}+H_{X(\mathbb{Z},w)}^{\infty,\pm}$ are closed subalgebras of $M_{X(\mathbb{Z},w)}$.

math.FA↗