Blue running of the primordial tensor spectrum

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We examine the possibility of positive spectral index of the power spectrum of the primordial tensor perturbation produced during inflation in the light of the detection of the B-mode polarization by the BICEP2 collaboration. We find a blue tilt is in general possible when the slow-roll parameter decays rapidly. We present two known examples in which a positive spectral index for the tensor power spectrum can be obtained. We also briefly discuss other consistency tests for further studies on inflationary dynamics.

Original languageEnglish
Article number022
JournalJournal of Cosmology and Astroparticle Physics
Issue number7
StatePublished - 1 Jul 2014


  • cosmological perturbation theory
  • inflation
  • physics of the early universe
  • primordial gravitational waves (theory)


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