  Recently, it was found by Greene and Levin that the Casimir energy of certain
combinations of massless and massive fields in space with extra dimensions play
a crucial role in the accelerated expansion of the late-time universe and
therefore it could serve as a candidate for the dark energy. It also provides a
mechanism in stabilizing the volume moduli of extra dimensions. However, the
shape moduli of the extra dimensions were never taken into account in the
previous work. We therefore study the stabilization mechanism for both volume
and shape moduli due to the Casimir energy in ${\mathbb M}^{1+3} \times
{\mathbb T}^{2}$. The result of our study shows that the previously known local
minimum is a saddle point. It is unstable to the perturbations in the direction
of the shape moduli. The new stable local minima stabilizes all the moduli and
drives the accelerating expansion of the universe. The cosmological dynamics
both in the bulk and the radion pictures are derived and simulated. The
equations of state for the Casimir energy in a general torus are derived. Shear
viscosity in extra dimensions induced by the Casimir density in the late times
is identified and calculated, it is found to be proportional to the Hubble
constant.
