Using the temperature data from Planck we search for departures from a power-law primordial power spectrum, employing Bayesian model-selection and posterior probabilities. We parametrize the spectrum with n knots located at arbitrary values of log k, with both linear and cubic splines. This formulation recovers both slow modulations and sharp transitions in the primordial spectrum. The power spectrum is well-fit by a featureless, power-law. A modulated primordial spectrum yields a better fit relative to Î›CDM at large scales, but there is no strong evidence for a departure from a power-law spectrum. Moreover, using simulated maps we show that a local feature can mimic the suppression of large-scale power. With multi-knot spectra we see only small changes in the posterior distributions for the other free parameters in the standard Î›CDM universe. We explore the degeneracy with other features of primordial power spectrum suppression, namely the effects of massive neutrinos.
Signals and degeneracies of the primordial power spectrum: Neutrinos & Inflation.
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