Double Field Theory with matter and its cosmological application
  We include matter in Double Field Theory (DFT) through a generalized
energy-momentum tensor written in terms of $O(D,D)$ multiplets, which mimics
the dynamics of a perfect fluid in the double geometry. From its divergence
equation we obtain the generalized energy conservation and Euler equations. In
order to construct cosmological solutions with matter, we present a space/time
split of DFT where a $O(1,1) \times O(D-1,D-1)$ symmetry is preserved. The
$O(1,1) \times O(D-1,D-1)$ generalized metric and the dilaton depend on both
$t$ and $\tilde t$, giving rise to a cosmological principle in the double
geometry. We compute the full form of the generalized Einstein equations with
matter. The parametrization of these solutions recovers string cosmologies upon
a suitable redefinition of the DFT energy density and pressure.
