Robust predictions for an oscillatory bispectrum in Planck 2015 data
  from transient reductions in the speed of sound of the inflaton
  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 $\ell\approx20$--$40$ minus/plus structure in Planck TT power spectrum, as
well as features spanning along the higher $\ell$'s ($\ell\approx100$--$1500$).
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.
