Non-Abelian Self-Dual Strings in Six Dimensions from Four Dimensional 1/2-BPS Monopoles

We explain a new construction of self-dual string solutions to the non-abelian two-form self-duality equation proposed in \cite{CK}. This class of self-dual strings is determined by the BPS monopoles in four-dimensions and the self dual string charge is given by the charge of the monopole. Our construction covers the SO(4) invariant self-dual string solutions found previously. We have also constructed, based on the 't Hooft-Polyakov monopole, a singular solution that describes two finitely separated M5-branes meeting midway in between. We comment that as BPS monopoles are generally given by the Nahm construction, our construction suggests that a generalized Nahm transform may exist for the non-abelian self-dual strings.