Multi-field DBI inflation: introducing bulk forms and revisiting the gravitational wave constraints

Understand

We study multi-field Dirac-Born-Infeld (DBI) inflation models, taking into account the NS-NS and R-R bulk fields present in generic flux compactifications.

• We compute the second-order action, which governs the behaviour of linear cosmological perturbations, as well as the third-order action, which can be used to calculate non-Gaussianities in these models.
• Remarkably, for scalar-type perturbations, we show that the contributions due to the various form fields exactly cancel in both the second- and third-order actions.
• Primordial perturbations and their non-Gaussianities are therefore unaffected by the presence of form fields and our previous results are unmodified.