Article ID Journal Published Year Pages File Type
1840960 Nuclear Physics B 2012 21 Pages PDF
Abstract

We study a multi-field inflationary theory with separable Lagrangian, which has different speed of sound for each field. We find that the fields always coupled at perturbative level through gravitational interaction. We show that if the coupling terms among the perturbation fields are weak enough, these fields can be treated as a combination of decoupled fields, which are similar to normal modes in coupled oscillation. By virtue of such fields, the curvature perturbation at horizon crossing can be calculated up to the leading order of slow-variation parameters via δNδN formalism. Explicitly, we consider a model of multi-speed DBI inflation, and calculate the power spectrum in detail. The result depends on the ratio of different speeds of sound, and shows an apparent amplification when the ratio deviates from unity.

Related Topics
Physical Sciences and Engineering Mathematics Mathematical Physics
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