Brane inflation, decay of D-branes, and reheating of the universe

In string theory realization of inflationary universe, one often encounters an unstable system of D-branes as a source of cosmological constant. The exit from such a brane inflation is triggered by decay of the unstable D-brane system and produces predominantly heavy closed string modes. This sets the initial condition for reheating, which becomes then the question of how these heavy strings decay down to lighter modes. For a realistic universe, the process has to be such that we find a universe whose expansion is mainly driven by Standard model particle content at least until the time of Nucleosynthesis. In this talk, we outline how the reheating of a realistic universe might be possible in the context of KKLMMT type scenarios, pointing out serious dangers of over-producing graviton sector particles and also of heavy relics.