The D-material universe
  In a previous publication by some of the authors (N.E.M., M.S. and M.F.Y.),
we have argued that the "D-material universe", that is a model of a brane world
propagating in a higher-dimensional bulk populated by collections of D-particle
stringy defects, provides a model for the growth of large-scale structure in
the universe via the vector field in its spectrum. The latter corresponds to
D-particle recoil velocity excitations as a result of the interactions of the
defects with stringy matter and radiation on the brane world. In this article,
we first elaborate further on the results of the previous study on the galactic
growth era and analyse the circumstances under which the D-particle recoil
velocity fluid may "mimic" dark matter in galaxies. A lensing phenomenology is
also presented for some samples of galaxies, which previously were known to
provide tension for modified gravity (TeVeS) models. The current model is found
in agreement with these lensing data. Then we discuss a cosmic evolution for
the D-material universe by analysing the conditions under which the late eras
of this universe associated with large-scale structure are connected to early
epochs, where inflation takes place. It is shown that inflation is induced by
dense populations of D-particles in the early universe, with the role of the
inflaton field played by the condensate of the D-particle recoil-velocity
fields under their interaction with relativistic stringy matter, only for
sufficiently large brane tensions and low string mass scales compared to the
Hubble scale. On the other hand, for large string scales, where the
recoil-velocity condensate fields are weak, inflation cannot be driven by the
D-particle defects alone. In such cases inflation may be driven by dilaton (or
other moduli) fields in the underlying string theory.
