# Semi-Fredholmness of weighted singular integral operators with shifts and slowly oscillating data

## TL;DR

This paper establishes conditions for the Fredholmness of certain weighted singular integral operators with shifts and slowly oscillating data on $L^p$ spaces, extending the understanding of their invertibility properties.

## Contribution

It provides new sufficient conditions for the Fredholmness of singular integral operators with shifts and slowly oscillating coefficients, broadening the class of operators with known invertibility criteria.

## Key findings

- Derived conditions for right and left Fredholmness on $L^p$ spaces.
- Analyzed operators with shifts having slowly oscillating discontinuities.
- Extended existing theory to include operators with more general oscillating data.

## Abstract

Let $\alpha,\beta$ be orientation-preserving homeomorphisms of $[0,\infty]$ onto itself, which have only two fixed points at $0$ and $\infty$, and whose restrictions to $\mathbb{R}_+=(0,\infty)$ are diffeomorphisms, and let $U_\alpha,U_\beta$ be the corresponding isometric shift operators on the space $L^p(\mathbb{R}_+)$ given by $U_\mu f=(\mu')^{1/p}(f\circ\mu)$ for $\mu\in\{\alpha,\beta\}$. We prove sufficient conditions for the right and left Fredholmness on $L^p(\mathbb{R}_+)$ of singular integral operators of the form $A_+P_\gamma^++A_-P_\gamma^-$, where $P_\gamma^\pm=(I\pm S_\gamma)/2$, $S_\gamma$ is a weighted Cauchy singular integral operator, $A_+=\sum_{k\in\mathbb{Z}}a_kU_\alpha^k$ and $A_-=\sum_{k\in\mathbb{Z}}b_kU_\beta^k$ are operators in the Wiener algebras of functional operators with shifts. We assume that the coefficients $a_k,b_k$ for $k\in\mathbb{Z}$ and the derivatives of the shifts $\alpha',\beta'$ are bounded continuous functions on $\mathbb{R}_+$ which may have slowly oscillating discontinuities at $0$ and $\infty$.