Quantum Spectrum of Instanton Solitons in Five Dimensional Noncommutative U(N) Theories

We explore quantum states of instanton solitons in five dimensional noncommutative Yang-Mills theories. We start with maximally supersymmetric U(N) theory compactified on a circle S^1, and derive the low energy dynamics of instanton solitons, or calorons, which is no longer singular. Quantizing the low energy dynamics, we find N physically distinct ground states with a unit Pontryagin number and no electric charge. These states have a natural D-string interpretation. The conclusion remains unchanged as we decompactify S^1, as long as we stay in the Coulomb phase by turning on adjoint Higgs expectation values.