Cecotti, Sergio; Cordova, Clay; Heckman, Johnatan J.; Vafa, Cumrun
(Springer, 2011-07)

We introduce T-branes, or "triangular branes," which are novel non-abelian
bound states of branes characterized by the condition that on some loci, their
matrix of normal deformations, or Higgs field, is upper triangular. ...