A gluing construction of singular solutions for a fully non-linear equation in conformal geometry

In this paper we study the ${\sigma }_2$–Yamabe equation, $n>4$, for solutions with a prescribed singular set $\mathrm{\Lambda }$ given by a disjoint union of closed submanifolds whose dimension is positive and strictly less than $(n-\sqrt{n}-2)\mathrm{/}2$. The ${\sigma }_2$–curvature in conformal geometry is defined as the second elementary symmetric polynomial of the eigenvalues of the Schouten tensor, which yields a fully non-linear PDE for the conformal factor. We show that the classical gluing method, used by Mazzeo-Pacard (JDG 1996) for the scalar curvature problem, can be used in the fully non-linear setting. This is a consequence of the conformal properties of the ${\sigma }_2$ equation, which imply that the linearized operator has good mapping properties in weighted spaces.