We present a new mechanism, the S-Track, to stabilize the volume modulus S in
heterotic M-theory flux compactifications along with the orbifold-size T
besides complex structure and vector bundle moduli stabilization. The key
dynamical ingredient which makes the volume modulus stabilization possible, is
M5-instantons arising from M5-branes wrapping the whole Calabi-Yau slice. These
are natural in heterotic M-theory where the warping shrinks the Calabi-Yau
volume along S^1/Z_2. Combined with H-flux, open M2-instantons and hidden
sector gaugino condensation it leads to a superpotential W which stabilizes S
similar like a racetrack but without the need for multi gaugino condensation.
Moreover, W contains two competing non-perturbative effects which stabilize T.
We analyze the potential and superpotentials to show that it leads to heterotic
de Sitter vacua with broken supersymmetry through non-vanishing F-terms.Comment: 16 pages, 2 figures; final PRD versio
