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 ${\beta }_{\mathrm{PPN}}$, ${\gamma }_{\mathrm{PPN}}$ with the charges of electric $H$ flux and dilaton respectively, and further relate them to stress-energy tensor. We show ${\beta }_{\mathrm{PPN}}=1$ from weak energy condition and argue that the observation of ${\gamma }_{\mathrm{PPN}}\simeq 1$ signifies the ultrarelativistic equation of state in baryons, or the suppression of gluon condensate.