The heterotic G$_2$ system with reducible characteristic holonomy
Mateo Galdeano, Leander Stecker
TL;DR
This work addresses constructing supersymmetric heterotic vacua with $G_2$-structure on seven-manifolds by exploiting almost contact geometries with reduced characteristic holonomy. It introduces a one-parameter family of $G_2$-connections $\nabla^{\lambda}$ and analyzes both exact and approximate solutions within the $3$-$(\alpha,\delta)$-Sasaki and $(\alpha,\delta)$-Sasaki frameworks, including a new exact solution in the degenerate case $\delta=0$ when $\alpha^2=1/(12\alpha')$. For the $\mathrm{Sp}(1)\mathrm{Sp}(1)$ branch, exact solutions are obtained in the degenerate setting while Bianchi-identity constraints yield interesting algebraic relations for $A$ and $\Theta$; for the $\mathrm{SU}(3)$ branch, $G_2$-instantons occur for specific $\lambda$ but exact Bianchi satisfaction is not achieved, though approximate solutions exist in special scaling limits. The results connect spinorial descriptions of $G_2$-structures with submersion geometry and highlight the role of $\alpha'$ in shaping the AdS$_3$ vacua and potential supersymmetry enhancements, offering a foundation for further moduli and Swampland investigations.
Abstract
We construct solutions to the heterotic G$_2$ system on almost contact metric manifolds with reduced characteristic holonomy. We focus on $3$-$(α,δ)$-Sasaki manifolds and $(α,δ)$-Sasaki manifolds, the latter being a convenient reformulation of spin $η$-Einstein $α$-Sasaki manifolds. Investigating a $1$-parameter family of G$_2$-connections on the tangent bundle, we obtain several approximate solutions as well as one new class of exact solutions on degenerate $3$-$(α,δ)$-Sasaki manifolds.
