Prospects of inflation in delicate D-brane cosmology

TL;DR

This paper explores multi-field D-brane inflation in a warped conifold, emphasizing the importance of proper field rotation for accurate inflation dynamics and analyzing the resulting density perturbation spectra.

Contribution

It demonstrates that a multi-field approach with a rotated field provides a more accurate inflation description than single-field models in D-brane cosmology.

Findings

Multi-field dynamics significantly differ from single-field approximations.

Proper field rotation yields a more accurate number of e-foldings.

Spectral index constraints are challenging to satisfy simultaneously.

Abstract

We study D-brane inflation in a warped conifold background that includes brane-position dependent corrections for the nonperturbative superpotential. Instead of stabilizing the volume modulus chi at instantaneous minima of the potential and studying the inflation dynamics with an effective single field (radial distance between a brane and an anti-brane) phi, we investigate the multi-field inflation scenario involving these two fields. The two-field dynamics with the potential V(phi,chi) in this model is significantly different from the effective single-field description in terms of the field phi when the field chi is integrated out. The latter picture underestimates the total number of e-foldings even by one order of magnitude. We show that a correct single-field description is provided by a field psi obtained from a rotation in the two-field space along the background trajectory. This model can give a large number of e-foldings required to solve flatness and horizon problems at the expense of fine-tunings of model parameters. We also estimate the spectra of density perturbations and show that the slow-roll parameter eta_{psi psi}=M_{pl}^2 V_{,psi psi}/V in terms of the rotated field psi determines the spectral index of scalar metric perturbations. We find that it is generally difficult to satisfy, simultaneously, both constraints of the spectral index and the COBE normalization, while the tensor to scalar ratio is sufficiently small to match with observations.