Non-Gaussianity in D3-brane inflation

Abstract

We update predictions for observables in the `delicate' D3/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 ζ power spectrum often cannot be approximated 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 f_NL≈ -(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 |fNL eq| ∼ 75 at kt/3 = 0.002 Mpc-1. 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.

String Cosmology: from the Early Universe to Today

“…[608,609,610]. On the other hand, the full 6-dimensional dynamics of warped D3-brane inflation has to be computed numerically and this has been done in [540,611,541,612,613].…”

Non-Gaussianity in rapid-turn multi-field inflation

“…the curvaton model [11][12][13][14], hybrid and multi-brid inflation [15][16][17][18][19], modulated and tachyonic (p)reheating scenarios [20][21][22][23][24][25][26]. Generating substantial levels of non-Gaussianity during a phase of multiple-field inflation is more challenging, as has been established in the simplest multi-field models and using general arguments [27][28][29][30][31][32][33][34][35][36][37][38][39], in studies of ultraviolet-motivated frameworks [40][41][42][43][44][45][46][47] as well as using a statistical approach with random potentials [48][49][50]. However, most studies to date have been limited to the slow-roll, slow-turn (SRST) approximation.…”