Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-12-07
JCAP 1103:034,2011
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
Typos corrected, references added. Minor changes and clarifications to match published version
Scientific paper
10.1088/1475-7516/2011/03/034
The Dirac-Born-Infeld (DBI) action has been widely studied as an interesting example of a model of k-inflation in which the sound speed of the cosmological perturbations differs from unity. In this article we consider a scalar-tensor theory in which the matter component is a field with a DBI action. Transforming to the Einstein frame, we explore the effect of the resulting coupling on the background dynamics of the fields and the first-order perturbations. We find that the coupling forces the scalar field into the minimum of its effective potential. While the additional scalar field contributes significantly to the energy density during inflation, the dynamics are determined by the DBI field, which has the interesting effect of increasing the number of efolds of inflation and decreasing the boost factor of the DBI field. Focusing on this case, we show, with the benefit of numerical examples, that the power spectrum of the primordial perturbations is determined by the behaviour of the perturbations of the modified DBI field.
Mota David F.
van de Bruck Carsten
Weller Joel M.
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