The period between inflation and nucleosynthesis can last for thirty orders of magnitude of time and represent half the lifetime of the universe on a logarithmic scale. But yet, there are minimal observational constraints on this epoch. String cosmologies motivate a rich set of modifications from the standard radiation-dominated post-inflationary assumption of Lambda CDM. In particular, string cosmology suggests the likelihood of moduli-dominated cosmologies through kination, tracker and matter epochs. I review the possible scenarios and observational possibilities, including a novel percolation scenario for formation of cosmic string networks.

TransPlanckian inflationary excursions are very interesting because they are sensitive to Planck-suppressed operators and can generate observable tensor modes. I review one proposed model generating a transPlanckian excursion and argue that consideration of antibrane backreaction renders the assumptions entering the model inconsistent.

Local string models are those where Standard Model degrees of freedom arise on a small region inside a large bulk volume. I study threshold effects on gauge coupling running for such models. The Kaplunovsky-Louis formula for locally supersymmetric gauge theories predicts the unification scale should be the bulk winding mode scale, parametrically large than the string scale where divergences are naively cut off. Analysis of explicit string models on orbifold/orientifold geometries confirms this. The winding mode scale arises from the presence of tadpoles uncancelled in the local model. I briefly discuss phenomenological applications to supersymmetry breaking and gauge coupling unification.