An exact solution of BPS domain wall junction

An exact solution of domain wall junction is obtained in a four-dimensional N=1 supersymmetric U(1)×U(1)′ gauge theory with three pairs of chiral superfields which is motivated by the N=2 SU(2) gauge theory with one flavor perturbed by an adjoint scalar mass. The solution allows us to evaluate various quantities including a new central charge Yk associated with the junction besides Zk which appears already in domain walls. We find that the new central charge Yk gives a negative contribution to the mass of the domain wall junction whereas the central charge Zk gives a dominant positive contribution. One has to be cautious to identify the central charge Yk alone as the mass of the junction.