Future constraints on neutrino isocurvature perturbations in the curvaton scenario

Abstract

In the curvaton scenario, residual isocurvature perturbations can be imprinted in the cosmic neutrino component after the decay of the curvaton field, implying in turn a non-zero chemical potential in the neutrino distribution. We study the constraints that future experiments like Planck, SPIDER or CMBPol will be able to put on the amplitude of isocurvature perturbations in the neutrino component. We express our results in terms of the square root γof the non-adiabaticity parameter αand of the extra relativistic degrees of freedom ΔN_eff. Assuming a fiducial model with purely adiabatic fluctuations, we find that Planck (SPIDER) will be able to put the following upper limits at the 1sigma level: γ< 5.3x10^-3 (1.2x10^-2) and ΔN_eff < 0.16 (0.40) . CMBPol will further improve these constraints to γ< 1.5x10^-3 and ΔN_eff < 0.043. Finally, we recast these bounds in terms of the background neutrino degeneracy parameter ξ and the corresponding perturbation amplitude σ_ξ, and compare with the bounds on ξ that can be derived from Big Bang Nucleosynthesis.

6 pages, 2 figures. References added. Matches version accepted for publication in Phys. Rev. D

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• Revealing the effects of curvature on the cosmological models
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• Quantifying the global "CMB tension" between the Atacama Cosmology Telescope and the Planck satellite in extended models of cosmology
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• Isocurvature modes in the CMB bispectrum
• Non-Gaussian isocurvature perturbations in dark radiation
• Constraints on neutrino density and velocity isocurvature modes from WMAP-9 data
• Lensing Bias to CMB Measurements of Compensated Isocurvature Perturbations
• Curvaton reheating in a Scale Invariant Two Measures Theory
• Probing a panoply of curvaton-decay scenarios using CMB data
• Planck constraints on neutrino isocurvature density perturbations
• Probing Lepton Asymmetry with 21 cm Fluctuations
• Generalized neutrino isocurvature