A tale of two modes: neutrino freestreaming in the early universe
Abstract
We present updated constraints on the freestreaming nature of cosmological neutrinos from cosmic microwave background (CMB) temperature and polarization power spectra, baryonic acoustic oscillation data, and distance ladder measurements of the Hubble constant. Specifically, we consider a Fermilike fourfermion interaction between massless neutrinos, characterized by an effective coupling constant G {sub eff}, and resulting in a neutrino opacity τdot {sub ν∝} G {sub eff}{sup 2} T {sub ν}{sup 5}. Using a conservative flat prior on the parameter log{sub 10}( G {sub eff} MeV{sup 2}), we find a bimodal posterior distribution with two clearly separated regions of high probability. The first of these modes is consistent with the standard ΛCDM cosmology and corresponds to neutrinos decoupling at redshift z {sub ν,dec} > 1.3×10{sup 5}, that is before the Fourier modes probed by the CMB damping tail enter the causal horizon. The other mode of the posterior, dubbed the 'interacting neutrino mode', corresponds to neutrino decoupling occurring within a narrow redshift window centered around z {sub ν,dec}∼8300. This mode is characterized by a high value of the effective neutrino coupling constant, log{sub 10}( G {sub eff} MeV{sup 2}) = −1.72 ± 0.10 (68% C.L.), together with a lower value of the scalarmore »
 Authors:
 McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States)
 Department of Physics, Harvard University, 17 Oxford St., Cambridge, MA 02138 (United States)
 Physics Department, University of California, Davis, CA 95616 (United States)
 Publication Date:
 OSTI Identifier:
 22676093
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 07; Other Information: Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; BARYONS; COMPARATIVE EVALUATIONS; COSMOLOGY; COUPLING CONSTANTS; DECOUPLING; DISTANCE; DISTRIBUTION; FERMI INTERACTIONS; FLUCTUATIONS; MAXIMUMLIKELIHOOD FIT; MEV RANGE; NEUTRINOS; OPACITY; OSCILLATIONS; POLARIZATION; RED SHIFT; RELICT RADIATION; SPECTRA; UNIVERSE
Citation Formats
Lancaster, Lachlan, CyrRacine, FrancisYan, Knox, Lloyd, and Pan, Zhen, Email: lachlanl@princeton.edu, Email: fcyrraci@physics.harvard.edu, Email: lknox@ucdavis.edu, Email: zhpan@ucdavis.edu. A tale of two modes: neutrino freestreaming in the early universe. United States: N. p., 2017.
Web. doi:10.1088/14757516/2017/07/033.
Lancaster, Lachlan, CyrRacine, FrancisYan, Knox, Lloyd, & Pan, Zhen, Email: lachlanl@princeton.edu, Email: fcyrraci@physics.harvard.edu, Email: lknox@ucdavis.edu, Email: zhpan@ucdavis.edu. A tale of two modes: neutrino freestreaming in the early universe. United States. doi:10.1088/14757516/2017/07/033.
Lancaster, Lachlan, CyrRacine, FrancisYan, Knox, Lloyd, and Pan, Zhen, Email: lachlanl@princeton.edu, Email: fcyrraci@physics.harvard.edu, Email: lknox@ucdavis.edu, Email: zhpan@ucdavis.edu. Sat .
"A tale of two modes: neutrino freestreaming in the early universe". United States.
doi:10.1088/14757516/2017/07/033.
@article{osti_22676093,
title = {A tale of two modes: neutrino freestreaming in the early universe},
author = {Lancaster, Lachlan and CyrRacine, FrancisYan and Knox, Lloyd and Pan, Zhen, Email: lachlanl@princeton.edu, Email: fcyrraci@physics.harvard.edu, Email: lknox@ucdavis.edu, Email: zhpan@ucdavis.edu},
abstractNote = {We present updated constraints on the freestreaming nature of cosmological neutrinos from cosmic microwave background (CMB) temperature and polarization power spectra, baryonic acoustic oscillation data, and distance ladder measurements of the Hubble constant. Specifically, we consider a Fermilike fourfermion interaction between massless neutrinos, characterized by an effective coupling constant G {sub eff}, and resulting in a neutrino opacity τdot {sub ν∝} G {sub eff}{sup 2} T {sub ν}{sup 5}. Using a conservative flat prior on the parameter log{sub 10}( G {sub eff} MeV{sup 2}), we find a bimodal posterior distribution with two clearly separated regions of high probability. The first of these modes is consistent with the standard ΛCDM cosmology and corresponds to neutrinos decoupling at redshift z {sub ν,dec} > 1.3×10{sup 5}, that is before the Fourier modes probed by the CMB damping tail enter the causal horizon. The other mode of the posterior, dubbed the 'interacting neutrino mode', corresponds to neutrino decoupling occurring within a narrow redshift window centered around z {sub ν,dec}∼8300. This mode is characterized by a high value of the effective neutrino coupling constant, log{sub 10}( G {sub eff} MeV{sup 2}) = −1.72 ± 0.10 (68% C.L.), together with a lower value of the scalar spectral index and amplitude of fluctuations, and a higher value of the Hubble parameter. Using both a maximum likelihood analysis and the ratio of the two mode's Bayesian evidence, we find the interacting neutrino mode to be statistically disfavored compared to the standard ΛCDM cosmology, and determine this result to be largely driven by the low l CMB temperature data. Interestingly, the addition of CMB polarization and direct Hubble constant measurements significantly raises the statistical significance of this secondary mode, indicating that new physics in the neutrino sector could help explain the difference between local measurements of H {sub 0}, and those inferred from CMB data. A robust consequence of our results is that neutrinos must be free streaming long before the epoch of matterradiation equality in order to fit current cosmological data.},
doi = {10.1088/14757516/2017/07/033},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 07,
volume = 2017,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}

Studies of neutrino asymmetries generated by ordinarysterile neutrino oscillations in the early Universe and implications for big bang nucleosynthesis bounds
Ordinarysterile neutrino oscillations can generate a significant lepton number asymmetry in the early Universe. We study this phenomenon in detail. We show that the dynamics of ordinarysterile neutrino oscillations in the early Universe can be approximately described by a single integrodifferential equation which we derive from both the density matrix and Hamiltonian formalisms. This equation reduces to a relatively simple ordinary firstorder differential equation if the system is sufficiently smooth (static limit). We study the conditions for which the static limit is an acceptable approximation. We also study the effect of the thermal distribution of neutrino momenta on the generationmore » 
Magnetically induced neutrino oscillations and neutrino refractive effects in the early Universe
We investigate neutrino spin precession in primordial magnetic fields, taking previously ignored neutrino refractive effects into account. A presentday intergalactic field strength B/sub 0/ implies that the magnetic dipole moments of any two neutrino species are bounded by ..mu../sub ..nu../approx. <10/sup 16/..mu../sub B/((10/sup 9/ G)/B/sub 0/) because of nucleosynthesis constraints on the number of neutrino flavors. 
Freestreaming approximation in early dynamics of relativistic heavyion collisions
We investigate an approximation to early dynamics in relativistic heavyion collisions, where after formation the partons are free streaming and around the proper time of 1 fm/c undergo a sudden equilibration described in terms of the Landau matching condition. We discuss physical and formal aspects of this approach. In particular, we show that initial azimuthally asymmetric transverse flow develops for noncentral collisions as a consequence of the sudden equilibration. Moreover, the energymomentum tensor from the freestreaming stage matches very smoothly to the form used in the transverse hydrodynamics, whereas matching to isotropic hydrodynamics requires a more pronounced change in themore »