Scalar Perturbation and Stability of Ricci Dark Energy

The Ricci dark energy (RDE) proposed to explain the accelerating expansion of the universe requires its parameter $\alpha <1$, whose value will determine the behavior of RDE. In this Letter, we study the scalar perturbation of RDE with and without matter in the universe, and we find that in both cases, the perturbation is stable if $\alpha >1\mathrm{/}3$, which gives a lower bound for $\alpha$ theoretically.