Robust predictions for an oscillatory bispectrum in Planck 2015 data from transient reductions in the speed of sound of the inflaton

Abstract

We update the search for features in the Cosmic Microwave Background (CMB) power spectrum due to transient reductions in the speed of sound, using Planck 2015 CMB temperature and polarisation data. We enlarge the parameter space to much higher oscillatory frequencies of the feature, and define a robust prior independent of the ansatz for the reduction, guaranteed to reproduce the assumptions of the theoretical model and exhaustive in the regime in which the feature is easily distinguishable from the baseline cosmology. We find a fit to the $\ell \approx 20$--$40$ minus/plus structure in Planck TT power spectrum, as well as features spanning along the higher $\ell$'s ($\ell \approx 100$--$1500$). For the last ones, we compute the correlated features that we expect to find in the CMB bispectrum, and asses their signal-to-noise and correlation to the ISW-lensing secondary bispectrum. We compare our findings to the shape-agnostic oscillatory template tested in Planck 2015, and we comment on some tantalising coincidences with some of the traits described in Planck's 2015 bispectrum data.

19 pages - matches published version

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Cited by in corpus (15)

• Planck 2018 results. X. Constraints on inflation
• Exploring Cosmic Origins with CORE: Inflation
• Probing primordial features with next-generation photometric and radio surveys
• Constraints on inflation with LSS surveys: features in the primordial power spectrum
• Euclid: The search for primordial features
• Bayesian reconstruction of the inflaton's speed of sound using CMB data
• Probing primordial features with the primary CMB
• Reconstructing the EFT of Inflation from Cosmological Data
• Final Thoughts on the Power Spectra of Scalar Potential Models
• From Non-trivial Geometries to Power Spectra and Vice Versa
• Scale invariance of the primordial tensor power spectrum
• Knot reconstruction of the scalar primordial power spectrum with Planck, ACT, and SPT CMB data
• Refining the nonlinear modelling of primordial oscillatory features
• Non-Gaussianity from Features
• Cross-tests of CMB features in the primordial spectra