Axions as Quintessence in String Theory
  We construct a model of quintessence in string theory based on the idea of
axion monodromy as discussed by McAllister, Silverstein and Westphal
arXiv:0808.0706. In the model, the quintessence field is an axion whose shift
symmetry is broken by the presence of 5-branes which are placed in highly
warped throats. This gives rise to a potential for the axion field which is
slowly varying, even after incorporating the effects of moduli stabilization
and supersymmetry breaking. We find that the resulting time dependence in the
equation of state of Dark Energy is potentially detectable, depending on the
initial conditions. The model has many very light extra particles which live in
the highly warped throats, but these are hard to detect. A signal in the
rotation of the CMB polarization can also possibly arise.
