$dS_5$ vacua from matter-coupled 5D N=4 gauged supergravity

We study $dS_5$ vacua within matter-coupled $N=4$ gauged supergravity in five dimensions using the embedding tensor formalism. With a simple ansatz for solving the extremization and positivity of the scalar potential, we derive a set of conditions for the gauged supergravity to admit $dS_5$ as maximally symmetric background solutions. The results provide a new approach for finding $dS_5$ vacua in five-dimensional $N=4$ gauged supergravity and explain a number of notable features pointed out in previous works. These conditions also determine the form of the gauge groups to be $SO(1,1)\times G_{\textrm{nc}}$ with $G_{\textrm{nc}}$ being a non-abelian non-compact group. In general, $G_{\textrm{nc}}$ can be a product of $SO(1,2)$ and a smaller non-compact group $G'_{\textrm{nc}}$ together with (possibly) a compact group. The $SO(1,1)$ factor is gauged by one of the six graviphotons, that is singlet under $SO(5)\sim USp(4)$ R-symmetry. The compact parts of $SO(1,2)$ and $G'_{\textrm{nc}}$ are gauged by vector fields from the gravity and vector multiplets, respectively. In addition, we explicitly study $dS_5$ vacua for a number of gauge groups and compute scalar masses at the vacua. As in the four-dimensional $N=4$ gauged supergravity, all the $dS_5$ vacua identified here are unstable.