B modes and the sound speed of primordial fluctuations

Gonzalo A. Palma and Alex Soto
Phys. Rev. D 91, 063525 – Published 20 March 2015

Abstract

It was recently shown that a large value of the tensor to scalar ratio r implies a constraint on the minimum value of the sound speed cs of primordial curvature perturbations during inflation that is stronger than current bounds coming from non-Gaussianity measurements. Here we consider additional aspects related to the measurement of B modes that may provide additional leverage to constrain the sound speed parametrizing noncanonical models of inflation. We find that a confirmation of the consistency relation r=8nt between the tensor to scalar ratio r and the tensor spectral index nt is not enough to rule out noncanonical models of inflation with a sound speed cs different from unity. To determine whether inflation was canonical or not, one requires knowledge of additional parameters, such as the running of the spectral index of scalar perturbations α. We also study how other parameters related to the ultraviolet completion of inflation modify the dependence of r on cs. For instance, we find that heavy degrees of freedom interacting with curvature fluctuations generically tend to make the constraint on the sound speed stronger. Our results, combined with future observations of primordial B modes, may help to constrain the background evolution of noncanonical models of inflation.

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  • Received 18 December 2014

DOI:https://doi.org/10.1103/PhysRevD.91.063525

© 2015 American Physical Society

Authors & Affiliations

Gonzalo A. Palma1 and Alex Soto2

  • 1Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Santiago, Chile
  • 2Departamento de Física, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Ñuñoa, Santiago, Chile

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Vol. 91, Iss. 6 — 15 March 2015

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