Naturally minute quantum correction to the cosmological constant descended from the hierarchy

We demonstrate that a naturally small quantum correction, or the Casimir energy, to the cosmological constant can arise from a massive bulk fermion field in the Randall-Sundrum model. Under the assumption that the ground value of four-dimensional effective cosmological constant is zero, which can only be attained by some other means, we show that its quantum correction originated from the Casimir energy, that is the vacuum energy associated with the nontrivial topology of the extra dimension, can be as small as the observed dark energy scale without fine-tuning of the bulk fermion mass. To ensure the stabilization of the system, we discuss two stabilization mechanisms under this setup. It is found that the Goldberger-Wise mechanism can be successfully introduced in the presence of a massive bulk fermion, without spoiling the smallness of the quantum correction.