Journal
PHYSICAL REVIEW D
Volume 95, Issue 4, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevD.95.043512
Keywords
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Funding
- ESA Member States
- DoE at the University of Michigan [DE-SC0007859]
- Michigan Center for Theoretical Physics
- Vetenskapsra det (Swedish Research Council) [638-2013-8993]
- Oskar Klein Centre for Cosmoparticle Physics
- ASI through ASI/INAF Agreement [2014-024-R.1]
- PROMETEO [II/2014/050]
- Spanish Grant of MINECO [FPA2014-57816-P]
- European Unions Horizon research and innovation programme under the Marie Skodowska-Curie Grant [690575, 674896]
- MINECO [SEV-2014-0398]
- NSF [AST1412966]
- NASA
- [NASA-EUCLID11-0004]
- [NSF AST1517593]
- [NSF AST14 12966]
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [1412966] Funding Source: National Science Foundation
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We study the impact of assumptions about neutrino properties on the estimation of inflationary parameters from cosmological data, with a specific focus on the allowed contours in the n(s)/r plane, where n(s) is the scalar spectral index and r is the tensor-to-scalar ratio. We study the following neutrino properties: (i) the total neutrino mass M-i = Sigma(i)m(i) (where the index i = 1, 2, 3 runs over the three neutrino mass eigenstates); (ii) the number of relativistic degrees of freedom N-eff at the time of recombination; and (iii) the neutrino hierarchy. Whereas previous literature assumed three degenerate neutrino masses or two massless neutrino species (approximations that clearly do not match neutrino oscillation data), we study the cases of normal and inverted hierarchy. Our basic result is that these three neutrino properties induce < 1 sigma shift of the probability contours in the n(s)/r plane with both current or upcoming data. We find that the choice of neutrino hierarchy (normal, inverted, or degenerate) has a negligible impact. However, the minimal cutoff on the total neutrino mass M-v,M-min = 0 that accompanies previous works using the degenerate hierarchy does introduce biases in the n(s)/r plane and should be replaced by M-v,M-min = 0.059 eV as required by oscillation data. Using current cosmic microwave background (CMB) data from Planck and Bicep/Keck, marginalizing over the total neutrino mass M-v and over r can lead to a shift in the mean value of ns of similar to 0.3 sigma toward lower values. However, once baryon acoustic oscillation measurements are included, the standard contours in the n(s)/r plane are basically reproduced. Larger shifts of the contours in the n(s)/r plane (up to 0.8 sigma) arise for nonstandard values of N-eff. We also provide forecasts for the future CMB experiments Cosmic Origins Explorer (COrE, satellite) and Stage-IV (ground-based) and show that the incomplete knowledge of neutrino properties, taken into account by a marginalization over M-v, could induce a shift of similar to 0.4 sigma toward lower values in the determination of ns (or a similar to 0.8 sigma shift if one marginalizes over N-eff). Comparison to specific inflationary models is shown. Imperfect knowledge of neutrino properties must be taken into account properly, given the desired precision in determining whether or not inflationary models match the future data.
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