Towards a measurement of the spectral runnings

Julian B. Munoz, Ely D. Kovetz, Alvise Raccanelli, Marc Kamionkowskia, Joseph Silk

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Single-field slow-roll ination predicts a nearly scale-free power spectrum of perturbations, as observed at the scales accessible to current cosmological experiments. This spectrum is slightly red, showing a tilt (1 1- n s ) ∼ 0:04. A direct consequence of this tilt are nonvanishing runnings α s = dn s =d log k, and β s = dα s =d log k, which in the minimal inationary scenario should reach absolute values of 10 -3 and 10 -5 , respectively. In this work we calculate how well future surveys can measure these two runnings. We consider a Stage-4 (S4) CMB experiment and show that it will be able to detect significant deviations from the inationary prediction for α s , although not for β s . Adding to the S4 CMB experiment the information from a WFIRST-like or a DESI-like survey improves the sensitivity to the runnings by ~ 20%, and 30%, respectively. A spectroscopic survey with a billion objects, such as the SKA, will add enough information to the S4 measurements to allow a detection of α s = 10 -3 , required to probe the single-field slow-roll inationary paradigm. We show that only a very-futuristic interferometer targeting the dark ages will be capable of measuring the minimal inationary prediction for βs. The results of other probes, such as a stochastic background of gravitational waves observable by LIGO, the Ly-α forest, and spectral distortions, are shown for comparison. Finally, we study the claims that large values of β s , if extrapolated to the smallest scales, can produce primordial black holes of tens of solar masses, which we show to be easily testable by the S4 CMB experiment.

Original languageEnglish
Article number032
JournalJournal of Cosmology and Astroparticle Physics
Issue number5
StatePublished - 16 May 2017
Externally publishedYes


  • Cosmological parameters from CMBR
  • Cosmological parameters from LSS
  • Galaxy surveys
  • Ination

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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