[in2p3-00804182] Planck 2013 results. XXII. Constraints on inflation

We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to n_s = 0.960 pm 0.0073, ruling out exact scale invariance at over 5 sigma. Planck establishes an upper bound on the tensor-to-scalar ratio at r < 0.11 (95% CL). Planck data shrink the space of allowed standard inflationary models, preferring potentials with V'' < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n > 2 do not provide a good fit to the data. Planck does not find any statistically significant running of the scalar spectral index, obtaining d n_s/d ln k = -0.0134 pm 0.0090. Several analyses dropping the slow-roll approximation are carried out, including detailed model comparison and inflationary potential reconstruction. We investigate whether the primordial power spectrum contains any features. A penalized likelihood approach suggests a feature near the smallest scales probed by Planck at an estimated significance of ~3 sigma after correction for the look elsewhere effect. Models with a parameterized oscillatory feature can improve the fit chi^2 by ~ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with bounds on f_NL measured by Planck. The fractional primordial contribution of CDM isocurvature modes in the curvaton and axion scenarios has upper bounds of 0.25% or 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelation can improve chi^2 by ~4 due to a moderate tension between l < 40 and higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions.



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