Resurrecting the Power-law, Intermediate, and Logamediate Inflations in the DBI Scenario with Constant Sound Speed

Understand

We investigate the power-law, intermediate, and logamediate inflationary models in the framework of DBI non-canonical scalar field with constant sound speed.

• In the DBI setting, we first represent the power spectrum of both scalar density and tensor gravitational perturbations.
• Then, we derive different inflationary observables including the scalar spectral index $n_s$, the running of the scalar spectral index $dn_s/d\ln k$, and the tensor-to-scalar ratio $r$.
• We show that the 95\% CL constraint of the Planck 2015 T+E data on the non-Gaussianity parameter $f_{{\rm NL}}^{{\rm DBI}}$ leads to the sound speed bound $c_{s}\geq0.087$ in the DBI inflation.