U-duality Between NCOS Theory and Matrix Theory

We show that the NCOS (noncommutative open string) theories on torus $T^p$ ($p\leq 5$) are U-dual to matrix theory on torus with electric flux background. Under U-duality, the number of D-branes and the number of units of electric flux get interchanged. Furthermore under the same U-duality the decoupling limit taken in the NCOS theory maps to the decoupling limit taken in the matrix theory, thus ensure the U-duality between those two class of theories. We consider the energy needed for Higgsing process and some bound states with finite energy and find agreements in both theories.