Non-Gaussianity in D3-brane inflation
  We update predictions for observables in the "delicate" D3/anti-D3
inflationary model on the conifold. We use a full CMB likelihood calculation to
assess goodness-of-fit, which is necessary because in this model the zeta power
spectrum often cannot be modelled as a power-law over observable scales. For
the first time we are able to provide accurate forecasts for the amplitude of
three-point correlations. In a significant portion of its parameter space the
model follows Maldacena's single-field prediction fNL ~ -(5/12)(ns-1) if nt <<
1. Therefore |fNL| is usually small when the power spectrum satisfies
observational constraints. In a small number of cases the bispectrum is instead
dominated by effects from rapid switching between angular minima. The resulting
amplitudes are larger, but mostly with unacceptable spectral behaviour. In the
most extreme case we obtain |fNLeq| ~ 75 at kt/3 = 0.002/Mpc. It has been
suggested that the quasi-single field inflation ("QSFI") mechanism could
produce significant 3-point correlations in this model. We do observe rare
shifts in amplitude between equilateral and squeezed configurations that could
possibly be associated with QSFI effects, but more investigation is needed to
establish the full bispectrum shape. There is evidence of "shape" running
between equilateral and squeezed configurations that may be inherited from the
scale dependence of the spectrum. We explore the dependence of observables on
discrete choices such as the truncation point of the potential. Our analysis
illustrates the advantages of a standard format for information exchange within
the inflationary model-building and testing community.
