The compactification from the eleven-dimensional Hov{r}ava-Witten orbifold to five-dimensional heterotic M-theory on a Schoen Calabi-Yau threefold is reviewed, as is the specific $SU(4)$ vector bundle leading to the heterotic standard model in the observable sector. Within the context of strongly coupled heterotic M-theory, a formalism for consistent hidden-sector bundles associated with a single line bundle is presented, and a specific line bundle is introduced as a concrete example. Anomaly cancellation and the associated bulk space five-branes are discussed in this context, as is the constraint that the hidden sector bundle be compatible with the slope-stability requirements of the observable sector $SU(4)$ gauge bundle. The further compactification to a four-dimensional effective theory on a linearized BPS double domain wall is then presented to order $kappa_{11}^{4/3}$. Specifically, the generic constraints required for anomaly cancellation and the restrictions imposed by positive squared gauge couplings to order $kappa_{11}^{4/3}$ are presented in detail. Three additional constraints are imposed, one guaranteeing that the $S^{1}/{mathbb{Z}}_{2}$ orbifold length is sufficiently larger than the average Calabi-Yau radius, and two enforcing that the hidden sector be compatible with both the unification mass scale and unified gauge coupling of the $SO(10)$ group in the observable sector. Finally, the expression for the Fayet-Iliopoulos term associated with an anomalous $U(1)$ symmetry is presented and its role in $N=1$ supersymmetry in the low-energy effective theory is discussed. It is shown that $N=1$ supersymmetry can be preserved by cancelling the tree-level and genus-one contributions against each another.
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