Bayesian reconstruction of the inflaton's speed of sound using CMB data

Abstract

We update the search for features, due to transient reductions in inflaton's speed of sound, in the Cosmic Microwave Background (CMB) angular power spectrum using Planck 2018 temperature, polarization and lensing data. We develop a new methodology to test more flexible templates to reconstruct the reduction of the speed of sound based on Gaussian Processes. We formally derive a dynamical prior for the shape of the reduction using a \textit{maximum-entropy} approach to ensure the physical conditions of the model are satisfied. The posterior allows for one or more consecutive reductions, fitting apparent features in the CMB power spectra in multipoles from a few tens to $\ell \simeq 2000$. As expected, these fits are not statistically favored with respect to the $\Lambda$CDM model. The methodology derived here allows for the inclusion of additional data sets (in particular, Large Scale Structure data), which in principle will increase the statistical significance of the reconstruction of the inflaton's speed of sound.

arXiv commentv2: 21 pages, 12 figures. Explanations extended in the 'methodology' section (where 2 new figures were included), added discussion in the 'consistency checks' section about the impact of running the analysis with separated TT and EE Planck 2018 data sets, updated some captions in figures for extra clarification

References in corpus (32)

• Planck 2018 results. X. Constraints on inflation
• The Effective Field Theory of Inflation
• Quantum Contributions to Cosmological Correlations
• Primordial Non-Gaussianities from Inflation Models
• Efficient sampling of fast and slow cosmological parameters
• PolyChord: nested sampling for cosmology
• PolyChord: next-generation nested sampling
• Features of heavy physics in the CMB power spectrum
• Uncorrelated Modes of the Nonlinear Power Spectrum
• Features and New Physical Scales in Primordial Observables: Theory and Observation
• Effective theories of single field inflation when heavy fields matter
• Mass hierarchies and non-decoupling in multi-scalar field dynamics
• On the importance of heavy fields during inflation
• Heavy fields, reduced speeds of sound and decoupling during inflation
• Correlating features in the primordial spectra
• Inflation with moderately sharp features in the speed of sound: GSR and in-in formalism for power spectrum and bispectrum
• Localized correlated features in the CMB power spectrum and primordial bispectrum from a transient reduction in the speed of sound
• Reconstruction of the primordial power spectrum of curvature perturbations using multiple data sets
• Bayesian inflationary reconstructions from Planck 2018 data
• Primordial power spectrum: a complete analysis with the WMAP nine-year data
• Untangling features in the primordial spectra
• Bounds on non-adiabatic evolution in single-field inflation
• Searching for primordial localized features with CMB and LSS spectra
• Cosmology-marginalized approaches in Bayesian model comparison: the neutrino mass as a case study
• Perturbative Unitarity of Inflationary Models with Features
• Direct search for features in the primordial bispectrum
• Robust predictions for an oscillatory bispectrum in Planck 2015 data from transient reductions in the speed of sound of the inflaton
• Red, Straight, no bends: primordial power spectrum reconstruction from CMB and large-scale structure
• Maximum-Entropy Priors with Derived Parameters in a Specified Distribution
• Probing primordial features with the primary CMB
• Reconstructing the EFT of Inflation from Cosmological Data
• Reconstruction of a direction-dependent primordial power spectrum from Planck CMB data

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• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Uncovering the History of Cosmic Inflation from Anomalies in Cosmic Microwave Background Spectra
• Primordial Standard Clock Models and CMB Residual Anomalies
• Comparing multi-field primordial feature models with the Planck data
• Euclid: The search for primordial features
• Learning how to surf: Reconstructing the propagation and origin of gravitational waves with Gaussian Processes
• Induced Gravitational Waves from Multi-Sound Speed Resonances during Cosmological Inflation
• Machine learning cosmic inflation
• High-resolution CMB bispectrum estimator with flexible modal basis
• Primordial feature constraints from BOSS+eBOSS
• Fingerprints of a Non-Inflationary Universe from Massive Fields
• Knot reconstruction of the scalar primordial power spectrum with Planck, ACT, and SPT CMB data
• Refining the nonlinear modelling of primordial oscillatory features
• Bayesian inference methodology for Primordial Power Spectrum reconstructions from Large Scale Structure
• Constraining the primordial power spectrum using a differentiable likelihood
• Inflation Story: slow-roll and beyond
• J-PAS: forecast on the primordial power spectrum reconstruction