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Planck 2018 results. X. Constraints on inflation

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abstract

We report on the implications for cosmic inflation of the 2018 Release of the Planck CMB anisotropy measurements. The results are fully consistent with the two previous Planck cosmological releases, but have smaller uncertainties thanks to improvements in the characterization of polarization at low and high multipoles. Planck temperature, polarization, and lensing data determine the spectral index of scalar perturbations to be $n_\mathrm{s}=0.9649\pm 0.0042$ at 68% CL and show no evidence for a scale dependence of $n_\mathrm{s}.$ Spatial flatness is confirmed at a precision of 0.4% at 95% CL with the combination with BAO data. The Planck 95% CL upper limit on the tensor-to-scalar ratio, $r_{0.002}<0.10$, is further tightened by combining with the BICEP2/Keck Array BK15 data to obtain $r_{0.002}<0.056$. In the framework of single-field inflationary models with Einstein gravity, these results imply that: (a) slow-roll models with a concave potential, $V" (\phi) < 0,$ are increasingly favoured by the data; and (b) two different methods for reconstructing the inflaton potential find no evidence for dynamics beyond slow roll. Non-parametric reconstructions of the primordial power spectrum consistently confirm a pure power law. A complementary analysis also finds no evidence for theoretically motivated parameterized features in the Planck power spectrum, a result further strengthened for certain oscillatory models by a new combined analysis that includes Planck bispectrum data. The new Planck polarization data provide a stringent test of the adiabaticity of the initial conditions. The polarization data also provide improved constraints on inflationary models that predict a small statistically anisotropic quadrupolar modulation of the primordial fluctuations. However, the polarization data do not confirm physical models for a scale-dependent dipolar modulation.

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  • abstract We report on the implications for cosmic inflation of the 2018 Release of the Planck CMB anisotropy measurements. The results are fully consistent with the two previous Planck cosmological releases, but have smaller uncertainties thanks to improvements in the characterization of polarization at low and high multipoles. Planck temperature, polarization, and lensing data determine the spectral index of scalar perturbations to be $n_\mathrm{s}=0.9649\pm 0.0042$ at 68% CL and show no evidence for a scale dependence of $n_\mathrm{s}.$ Spatial flatness is confirmed at a precision of 0.4% at 95% CL w
  • background Mike Stillman, "The Kreuzer-Skarke Axiverse," JHEP 04, 138 (2020), arXiv:1808.01282 [hep-th]. [42] Mehmet Demirtas, Andres Rios-Tascon, and Liam McAllister, "CYTools: A Software Package for Analyz- ing Calabi-Yau Manifolds," (2022), arXiv:2211.03823 [hep-th]. [43] Prateek Agrawal, Michael Nee, and Mario Reig, "Ax- ion Couplings in Heterotic String Theory," (2024), arXiv:2410.03820 [hep-ph]. [44] Mario Reig and Timo Weigand, "Testing the Het- erotic String with the Axion-Photon Coupling," (2025),

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Spectral solution of the Fokker-Planck operator for hilltop constant-roll inflation shows rare crossing trajectories dominate the mean, so the median yields a coarse-grained ΔN distribution whose exponential tail flattens into a peak near maximal value.

citing papers explorer

Showing 50 of 150 citing papers.

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  • Inverse-Scattering Reconstruction of Inflation from Scalar and Tensor Primordial Spectra astro-ph.CO · 2026-06-05 · unverdicted · none · ref 9 · internal anchor

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  • Probing the small-scale primordial power spectrum via relic neutrinos and acoustic reheating hep-ph · 2026-05-12 · unverdicted · none · ref 2 · internal anchor

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