Dp-D(p+4) in Noncommutative Yang-Mills
An anti-self-dual instanton solution in Yang-Mills theory on noncommutative ${\R}^4$ with an anti-self-dual noncommutative parameter is constructed. The solution is constructed by the ADHM construction and it can be treated in the framework of the IIB matrix model. In the IIB matrix model, this solution is interpreted as a system of a Dp-brane and D(p+4)-branes, with the Dp-brane dissolved in the worldvolume of the D(p+4)-branes. The solution has a parameter that characterises the size of the instanton. The zero of this parameter corresponds to the singularity of the moduli space. At this point, the solution is continuously connected to another solution which can be interpreted as a system of a Dp-brane and D(p+4)-branes, with the Dp-brane separated from the D(p+4)-branes. It is shown that even when the parameter of the solution comes to the singularity of the moduli space, the gauge field itself is non-singular. A class of multi-instanton solutions is also constructed.