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