Spin Dynamics of t-J Model on Triangular Lattice

We study the spin dynamics of t-J model on triangular lattice in the Slave-Boson-RPA scheme in light of the newly discovered superconductor Na$_{x}$CoO$_{2}$. We find resonant peak in the dynamic spin susceptibility in the $d+id^{^{\prime}}$-wave superconducting state for both hole and electron doping in large doping range. We find the geometrical frustration inherent of the triangular lattice provide us a unique opportunity to discriminate the SO(5) and RPA-like intepretation of the origin of the resonant peak.