Warm DBI inflation with constant sound speed

TL;DR

This paper investigates warm DBI inflation with constant sound speed, showing it can align with Planck 2015 data in certain regimes and potentially address swampland conjectures, unlike cold DBI inflation.

Contribution

It demonstrates that warm DBI inflation with constant sound speed can be compatible with observational data and offers a solution to the swampland conjecture, unlike cold DBI inflation.

Findings

Warm DBI inflation fits Planck data in intermediate/high dissipation regimes.

Cold DBI inflation conflicts with Planck observational constraints.

Warm DBI predicts scalar spectral index running consistent with observations.

Abstract

We study inflation with the Dirac-Born-Infeld (DBI) noncanonical scalar field in both the cold and warm scenarios. We consider the Anti-de Sitter warp factor $f(\phi)=f_{0}/\phi^{4}$ for the DBI inflation and check viability of the quartic potential $V(\phi)=\lambda\phi^{4}/4$ in light of the Planck 2015 observational results. In the cold DBI setting, we find that the prediction of this potential in the $r-n_s$ plane is in conflict with Planck 2015 TT,TE,EE+lowP data. This motivates us to focus on the warm DBI inflation with constant sound speed. We conclude that in contrary to the case of cold scenario, the $r-n_s$ result of warm DBI model can be compatible with the 68\% CL constraints of Planck 2015 TT,TE,EE+lowP data in the intermediate and high dissipation regimes, whereas it fails to be observationally viable in the weak dissipation regime. Also, the prediction of this model for the running of the scalar spectral index $dn_s/d\ln k$ is in good agreement with the constraint of Planck 2015 TT,TE,EE+lowP data. Finally, we show that the warm DBI inflation can provide a reasonable solution to the swampland conjecture that challenges the de Sitter limit in the standard inflation.