Signatures of relativistic neutrinos in CMB anisotropy and matter clustering

By S. Bashinsky, Uros Seljak. 2003

246 citations recorded by the source corpus.

We present a detailed analytical study of ultrarelativistic neutrinos in cosmological perturbation theory and of the observable signatures of inhomogeneities in the cosmic neutrino background. We note that modification of perturbation variables that removes all the time derivatives of scalar gravitational potentials from the dynamical equations simplifies their solution notably. The used perturbations of particle number per coordinate, not proper, volume are generally constant on superhorizon scales. In real space the analytical approach can be extended beyond fluid models to neutrinos. The faster cosmological expansion due to the neutrino background affects the acoustic and damping angular scales of the cosmic microwave background (CMB). But we find that equivalent changes can be produced by varying other standard parameters, including the primordial helium abundance. The low-l integrated Sachs-Wolfe effect is also not sensitive to neutrinos. However, the gravity of neutrino perturbations suppresses the CMB acoustic peaks for the multipoles with $l\ensuremath{\gtrsim}200$ while it enhances the amplitude of matter fluctuations on these scales. In addition, the perturbations of relativistic neutrinos generate a unique phase shift of the CMB acoustic oscillations that, for adiabatic modes, cannot be caused by any other standard physics. The origin of the shift is traced to neutrino free-streaming velocity exceeding the sound speed of the photon-baryon plasma. We find that from a high-resolution, low-noise instrument such as CMBPOL the effective number of light neutrino species can be determined with an accuracy of $\ensuremath{\sigma}{(N}_{\ensuremath{\nu}})\ensuremath{\simeq}0.05\char21{}0.09,$ depending on the constraints on the helium abundance.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/838d511872aa65f72429f85fdce2df72191ef2c5

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Citations in the corpus

Sounds Discordant: Classical Distance Ladder and ΛCDM-based Determinations of the Cosmological Sound Horizon (2018, background): “One of the hindrances to adjustment of Neff is that it leads to a change in the ratio of sound horizon to damping scales (Hu & White 1996; Bashinsky & Seljak 2004; Hou et al. 2013), a change that is not preferred by CMB data.”
The DESI Experiment Part I: Science,Targeting, and Survey Design (2016, background): “The detection of any discrepancy from the expected value would be a truly major result, as it would indicate a sterile neutrino [167], a decaying particle [168], a nonstandard thermal history [169], or perhaps that dark energy does not fade away to ∼ 10−9 at the time of recombination as expected for”
COSMOLOGICAL CONSTRAINTS FROM GALAXY CLUSTERS IN THE 2500 SQUARE-DEGREE SPT-SZ SURVEY (2016, background): “This mechanism results in strong degeneracies between Neff and other cosmological parameters, notably H0 and σ8, when considering CMB data alone (e.g., Bashinsky & Seljak 2004).”
ACTPol: a polarization-sensitive receiver for the Atacama Cosmology Telescope (2010, background): “, gravitons, Goldstone bosons) could contribute to the radiation density or non-standard neutrino interactions could exist that would alter Neff , either of which would induce a distinct phase shift in the positions of the acoustic peaks.(30) Current constraints from WMAP and other cosmological data”
FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2008, unknown): “The anisotropic stress of neutrinos also leaves distinct signatures in the CMB power spectrum, which is not degenerate with Ωmh 2 (Hu et al. 1995; Bashinsky & Seljak 2004).”
Large-Angle Anomalies in the CMB (2010, background): “Therefore, as expected Galactic foregrounds lead to Galactic, and not ecliptic, correlations of the quadrupole and octopole (see also studies by [49, 50]).”