General Analysis of Dark Radiation in Sequestered String Models
  We perform a general analysis of axionic dark radiation produced from the
decay of the lightest modulus in the sequestered LARGE Volume Scenario. We
discuss several cases depending on the form of the Kahler metric for visible
sector matter fields and the mechanism responsible for achieving a de Sitter
vacuum. The leading decay channels which determine dark radiation predictions
are to hidden sector axions, visible sector Higgses and SUSY scalars depending
on their mass. We show that in most of the parameter space of split SUSY-like
models squarks and sleptons are heavier than the lightest modulus. Hence dark
radiation predictions previously obtained for MSSM-like cases hold more
generally also for split SUSY-like cases since the decay channel to SUSY
scalars is kinematically forbidden. However the inclusion of string loop
corrections to the Kahler potential gives rise to a parameter space region
where the decay channel to SUSY scalars opens up, leading to a significant
reduction of dark radiation production. In this case, the simplest model with a
shift-symmetric Higgs sector can suppress the excess of dark radiation $\Delta
N_{eff}$ to values as small as 0.14, in perfect agreement with current
experimental bounds. Depending on the exact mass of the SUSY scalars all values
in the range 0.14 $\lesssim \Delta N_{eff} \lesssim$ 1.6 are allowed.
Interestingly dark radiation overproduction can be avoided also in the absence
of a Giudice-Masiero coupling.
