# Fractional Yamabe problem on locally flat conformal infinities of Poincare-Einstein manifolds

## TL;DR

This paper addresses the fractional Yamabe problem on locally flat conformal infinities of Poincaré-Einstein manifolds, demonstrating existence results without relying on the positive mass theorem by employing algebraic topological methods.

## Contribution

It extends the fractional Yamabe problem to locally flat conformal infinities of Poincaré-Einstein manifolds and introduces a topological approach to overcome the positive mass theorem limitation.

## Key findings

- Existence of constant fractional scalar curvature metrics on the specified conformal infinities.
- Application of algebraic topological methods to bypass positive mass theorem constraints.
- Addresses both 2-dimensional and higher-dimensional cases of the problem.

## Abstract

We study in this paper the fractional Yamabe problem first considered by Gonzalez-Qing on the conformal infinity $(M^n , [h])$ of a Poincar\'e-Einstein manifold $(X^{n+1} , g^+ )$ with either $n = 2$ or $n \geq 3$ and $(M^n , [h])$ is locally flat - namely $(M, h)$ is locally conformally flat. However, as for the classical Yamabe problem, because of the involved quantization phenomena, the variational analysis of the fractional one exhibits also a local situation and a global one. Furthermore the latter global situation includes the case of conformal infinities of Poincar\'e-Einstein manifolds of dimension either 2 or of dimension greater than $2$ and which are locally flat, and hence the minimizing technique of Aubin- Schoen in that case clearly requires an analogue of the positive mass theorem of Schoen-Yau which is not known to hold. Using the algebraic topological argument of Bahri-Coron, we bypass the latter positive mass issue and show that any conformal infinity of a Poincar\'e-Einstein manifold of dimension either $n = 2$ or of dimension $n \geq 3$ and which is locally flat admits a Riemannian metric of constant fractional scalar curvature.