Non-perturbative Aspects of Kaluza-Klein Modes in Five-dimensional Supersymmetric QCD on S¹

We study the stability of Kaluza-Klein (KK) modes in five-dimensional N=1 supersymmetric QCD compactified on S^1 using the D3-brane probe realization. We find a phenomenon in which the quark KK mode with the KK number n=1 decays while other KK modes are stable. This is contrary to the ordinary assumption that the state with n=1 is the most stable in quark KK modes. In addition, we show that a massive gauge singlet state carrying the KK number exists stably. This provides a proper candidate for dark matter.