Instantons, five-branes and fractional strings

Abstract

In this note I review the construction of higher-dimensional instantons and heterotic NS5-branes on Ricci-flat cones from arXiv:1109.3552, as well as fractional strings from arXiv:1202.5046. The focus is on methods and interpretation. I show, furthermore, that smeared 5-brane supergravity solutions on manifolds with holonomy G2 or Spin(7) can be obtained quite generally by a conformal deformation of the Ricci-flat metric, whereas Calabi-Yau and hyperk\"ahler manifolds require more sophisticated deformations and a case by case treatment.