Extended period domains and algebraic groups

For a linear algebraic group $G$ over $\mathbf Q$, we consider the period domains $D$ classifying $G$-mixed Hodge structures, and construct the extended period domains $D_{\Sigma}$. In particular, we give toroidal partial compactifications of mixed Mumford--Tate domains, mixed Shimura varieties over $\mathbf C$, and higher Albanese manifolds.