Two Massive and One Massless Sp(4) Monopoles

Starting from Nahm's equations, we explore BPS magnetic monopoles in the Yang-Mills Higgs theory of gauge group $Sp(4)$ which is broken to $SU(2)\times U(1)$. A family of BPS field configurations with purely Abelian magnetic charge describe two identical massive monopoles and one massless monopole. We construct the field configurations with axial symmetry by employing the ADHMN construction, and find the explicit expression of the metrics for the 12-dimensional moduli space of Nahm data and its submanifolds.