Non-Gaussianity in D3-brane inflation

Abstract

We update predictions for observablesin the `delicate' D3/D3inflationary model on the conifold.We use a full CMB likelihood calculation to assessgoodness-of-fit, which is necessary becausein this model theζpower spectrum often cannot be approximated as a power-law overobservable scales.For the first time we are able to provideaccurate forecasts forthe amplitude of three-pointcorrelations.In a significant portion of its parameterspace the model follows Maldacena's single-fieldprediction f_NL≈ -(5/12)(ns-1)if|nt| ≪ 1.Therefore|fNL| is usually small whenthe power spectrum satisfies observationalconstraints.In a small number of casesthe bispectrum is instead dominated byeffects from rapid switching between angular minima.The resulting amplitudes are larger,but mostly with unacceptable spectral behaviour.In the most extreme casewe obtain |fNL eq| ∼ 75at kt/3 = 0.002 Mpc-1.It has been suggested that the quasi-singlefield inflation (`QSFI') mechanism couldproduce significant 3-point correlations in this model.We do observe rare shifts in amplitude betweenequilateral and squeezed configurations that couldpossibly be associated with QSFI effects, butmore investigation is needed to establish the fullbispectrum shape.There is evidence of `shape' running between equilateraland squeezed configurations that maybe inheritedfrom the scale dependence of the spectrum.We explore the dependence of observables on discrete choicessuch as the truncation point of the potential.Our analysis illustrates the advantages of a standardformat for information exchange within theinflationary model-building and testing community.