Etudes on cosmological moduli dynamics

In this thesis we study the problem of moduli stabilisation in a cosmological context of string theory. Motivated by the problem of giving these fields large masses, we introduce for the first time chameleon fields, so named because their masses and values depend sensitively on the local matter density. We show that such fields can evade all local tests of the equivalence principle and we make predictions for near-future tests of gravity in space. We also show that the chameleon field can drive the current phase of cosmic accelerated expansion. As such we provide an explicit realisation of a quintessence model where the quintessence field couples directly to baryons and dark matter with gravitational strength. Remarkably, we find the range of allowed initial conditions leading to a successful cosmology is wider than in usual quintessence. We then turn our attention to racetrack inflation, a proposal for inflationary dynamics in the context of flux compactifications. We show that the inclusion of string corrections can destroy the conditions necessary for both stabilisation and inflation in a region of moduli space where a classical supergravity analysis is stable to such corrections. Finally, we study a truncated low energy effective action that models the neighbourhood of special points in moduli space, such as conifold points, where extra massless degrees of freedom arise. We study moduli dynamics and stabilisation in this context in a cosmological background and find surprising variety in field dynamics including the appearance of chaos. The chaos aids in our understanding of the behaviour of moduli near these special points. In particular we find a viable mechanism for trapping some of the moduli near these points.