The intrinsic bispectrum of the CMB from isocurvature initial conditions

Abstract

Non-linear effects in the early Universe generate non-zero bispectra of the cosmic microwave background (CMB) temperature and polarization, even in the absence of primordial non-Gaussianity. In this paper, we compute the contributions from isocurvature modes to the CMB bispectra using a modified version of the second-order Boltzmann solver SONG. We investigate the ability of current and future CMB experiments to constrain these modes with observations of the bispectrum. Our results show that the enhancement due to single isocurvature modes mixed with the adiabatic mode is negligible for the parameter ranges currently allowed by the most recent Planck results. However, we find that a large compensated isocurvature mode can produce a detectable bispectrum when its correlation with the adiabatic mode is appreciable. The non-observation of this contribution in searches for the lensing bispectrum from Planck allows us to place a new constraint on the relative amplitude of the correlated part of the compensated isocurvature mode of $f_{\mathrm{CIP}}=1\pm 100$. We compute forecasts for future observations by COrE, SO, CMB-S4 and an ideal experiment and conclude that a dedicated search for the bispectrum from compensated modes could rule out a number of scenarios realised in the curvaton model. In addition, the CMB-S4 experiment could detect the most extreme of those scenarios ($f_{\mathrm{CIP}}=16.5$) at 2 to 3-$\sigma$ significance.

arXiv comment22 pages, 13 figures. V2: Additional clarifications and details. Matches version published in JCAP

References in corpus (66)

• Planck 2018 results. X. Constraints on inflation
• The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes
• The Simons Observatory: Science goals and forecasts
• The Cold Dark Matter Density Perturbation
• Cosmological perturbations
• The Cosmic Linear Anisotropy Solving System (CLASS) I: Overview
• BICEP2 / Keck Array x: Constraints on Primordial Gravitational Waves using Planck, WMAP, and New BICEP2/Keck Observations through the 2015 Season
• CMB-S4 Science Case, Reference Design, and Project Plan
• Mission design of LiteBIRD
• The General Primordial Cosmic Perturbation
• The Observed Squeezed Limit of Cosmological Three-Point Functions
• Large-scale curvature and entropy perturbations for multiple interacting fluids
• The shape of the CMB lensing bispectrum
• General CMB and Primordial Bispectrum Estimation I: Mode Expansion, Map-Making and Measures of f_NL
• Planck 2018 results. IX. Constraints on primordial non-Gaussianity
• Observational constraints on the curvaton model of inflation
• Planck 2013 results. VI. High Frequency Instrument data processing
• Exploring Cosmic Origins with CORE: Cosmological Parameters
• Adiabatic and entropy perturbations with interacting fluids and fields
• Evolution of cosmological dark matter perturbations
• An Isocurvature CDM Cosmogony. I. A Worked Example of Evolution Through Inflation
• The radiative transfer at second order: a full treatment of the Boltzmann equation with polarization
• CMB 3-point functions generated by non-linearities at recombination
• PICO: Probe of Inflation and Cosmic Origins
• The CMB bispectrum in the squeezed limit
• Sachs-Wolfe at second order: the CMB bispectrum on large angular scales
• The intrinsic bispectrum of the Cosmic Microwave Background [PhD thesis]
• The real shape of non-Gaussianities
• Compensated Isocurvature Perturbations and the Cosmic Microwave Background
• The CMB bispectrum from recombination
• Non-Gaussianity in the Cosmic Microwave Background Anisotropies at Recombination in the Squeezed limit
• Forecasted 21 cm constraints on compensated isocurvature perturbations
• Non-Gaussianity and the CMB Bispectrum: confusion between Primordial and Lensing-Rees Sciama contribution?
• Search for Compensated Isocurvature Perturbations with Planck Power Spectra
• The full squeezed CMB bispectrum from inflation
• Vorticity generation at second order in cosmological perturbation theory
• Baryons do trace dark matter 380,000 years after the big bang: Search for compensated isocurvature perturbations with WMAP 9-year data
• Boltzmann hierarchy for the cosmic microwave background at second order including photon polarization
• On Possible Variation in the Cosmological Baryon Fraction
• Compensated isocurvature perturbations in the curvaton model
• Probing correlated compensated isocurvature perturbations using scale-dependent galaxy bias
• Baryon-CDM isocurvature galaxy bias with IllustrisTNG
• The intrinsic B-mode polarisation of the Cosmic Microwave Background
• Power Spectra Based Planck Constraints on Compensated Isocurvature, and Forecasts for LiteBIRD and CORE Space Missions
• Impact of polarisation on the intrinsic CMB bispectrum
• Do baryons trace dark matter in the early universe?
• Baryons still trace dark matter: probing CMB lensing maps for hidden isocurvature
• Minimizing gravitational lensing contributions to the primordial bispectrum covariance
• Estimating the amount of vorticity generated by cosmological perturbations in the early universe
• Vector and tensor contributions to the curvature perturbation at second order
• The full CMB temperature bispectrum from single-field inflation
• Geodesic "curve"-of-sight formulae for the cosmic microwave background: a unified treatment of redshift, time delay, and lensing
• Optimal bispectrum estimator and simulations of the the CMB Lensing-ISW non-Gaussian signal
• Lensing Bias to CMB Measurements of Compensated Isocurvature Perturbations
• Formulating Weak Lensing from the Boltzmann Equation and Application to Lens-lens Couplings
• A new line-of-sight approach to the non-linear Cosmic Microwave Background
• Compensated Isocurvature Perturbations in the Galaxy Power Spectrum
• BAO Modulation as a Probe of Compensated Isocurvature Perturbations
• CMB Bispectrum from Non-linear Effects during Recombination
• Exploring compensated isocurvature perturbations with CMB spectral distortion anisotropies
• On the Effects due to a Decaying Cosmological Fluctuation
• Testing gravity with non-Gaussianity
• Isocurvature initial conditions for second order Boltzmann solvers
• Magnetogenesis from isocurvature initial conditions
• Initial conditions of the universe: A sign of the sine mode
• Initial conditions of the universe: Decaying tensor modes