# A construction of hyperk\"ahler metrics through Riemann-Hilbert problems II

## TL;DR

This paper develops the Riemann-Hilbert problem framework necessary for constructing hyperk"ahler metrics, focusing on solving non-linear problems, analyzing limit cases, and ensuring solution smoothness.

## Contribution

It introduces methods to solve non-linear Riemann-Hilbert problems with discontinuities and zeroes, advancing the mathematical tools for hyperk"ahler metric construction.

## Key findings

- Solutions obtained via contraction principles and saddle-point estimates.
- Smoothness of solutions established through compactness arguments.
- Handling of limit cases with discontinuities and zeroes in jump functions.

## Abstract

We develop the theory of Riemann-Hilbert problems necessary for the results in part one of this series of papers. In particular, we obtain solutions for a family of non-linear Riemann-Hilbert problems through classical contraction principles and saddle-point estimates. We use compactness arguments to obtain the required smoothness property on solutions. We also consider limit cases of these Riemann-Hilbert problems where the jump function develops discontinuities of the first kind together with zeroes of a specific order at isolated points in the contour. Solutions through Cauchy integrals are still possible and they have at worst a branch singularity at points where the jump function is discontinuous and a zero for points where the jump vanishes.