Post-Newtonian Feasibility of the Closed String Massless Sector

We perform post Newtonian analysis of Double Field Theory as a test of string theory in gravitational sector against observations. We identify the Eddington--Robertson--Schiff parameters $\beta_{{{\rm{PPN}}}}$, $\gamma_{{{\rm{PPN}}}}$ with the charges of electric $H$-flux and dilaton respectively, and further relate them to stress-energy tensor. We show ${\beta_{{{\rm{PPN}}}}=1}$ from weak energy condition and argue that the observation of $\gamma_{{{\rm{PPN}}}}\simeq 1$ signifies the ultrarelativistic equation of state in baryons, or the suppression of gluon condensate.