Understand
We study cosmological perturbations in general inflation models with multiple scalar fields and arbitrary kinetic terms, with special emphasis on the multi-field extension of Dirac-Born-Infeld (DBI) inflation.
- We compute the second-order action governing the dynamics of linear perturbations in the most general case.
- Specializing to DBI, we show that the adiabatic and entropy modes propagate with a {\it common} effective sound speed and are thus amplified at sound horizon crossing.
- In the small sound speed limit, we find that the amplitude of the entropy modes is much higher than that of the adiabatic modes.
Reading the bibliography…