{
  "id": "1306.1536",
  "version": "v2",
  "published": "2013-06-06T20:00:05.000Z",
  "updated": "2014-12-06T19:16:37.000Z",
  "title": "Limits on Neutrino-Neutrino Scattering in the Early Universe",
  "authors": [
    "Francis-Yan Cyr-Racine",
    "Kris Sigurdson"
  ],
  "comment": "9 Pages, 4 figures, 1 table. v2: Version accepted for publication, enhanced discussion on neutrino interaction beyond the SM, enhanced figures, references added",
  "categories": [
    "astro-ph.CO",
    "hep-ph"
  ],
  "abstract": "In the standard model neutrinos are assumed to have streamed across the Universe since they last scattered at the weak decoupling epoch when the temperature of the standard-model plasma was ~MeV. The shear stress of free-streaming neutrinos imprints itself gravitationally on the Cosmic Microwave Background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free-streaming until a much later epoch. We use observations of the CMB to constrain the strength of neutrino self-interactions G_eff and put limits on new physics in the neutrino sector from the early Universe. Recent measurements of the CMB at large multipoles made by the Planck satellite and high-l experiments are critical for probing this physics. Within the context of conventional LambdaCDM parameters cosmological data are compatible with G_eff < 1/(56 MeV)^2 and neutrino free-streaming might be delayed until their temperature has cooled to as low as ~25 eV. Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z~10^4 with a preferred interaction strength in a narrow region around $G_{\\rm eff} \\simeq 1/({\\rm 10 \\, MeV})^{2} \\simeq 8.6\\times10^8 G_{\\rm F}$, where $G_{\\rm F}$ is the Fermi constant. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. While we phrase our discussion here in terms of a specific scenario in which a late onset of neutrino free-streaming could occur, our constraints on the neutrino visibility function are very general.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2013-06-06T20:00:05.000Z",
      "abstract": "In the standard model neutrinos are assumed to have streamed across the Universe since they last scattered at the weak decoupling epoch when the temperature of the standard-model plasma was ~MeV. The shear stress of free-streaming neutrinos imprints itself gravitationally on the Cosmic Microwave Background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free-streaming until a much later epoch. We use observations of the CMB to constrain the strength of neutrino self-interactions G_eff and put limits on new physics in the neutrino sector from the early Universe. Recent measurements of the CMB at large multipoles made by the Planck satellite and high-l experiments are critical for probing this physics. Within the context of conventional LambdaCDM parameters cosmological data are compatible with G_eff < 1/(56 MeV)^2 and neutrino free-streaming might be delayed until their temperature has cooled to as low as ~25 eV. Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z~10^4 with a preferred interaction strength in a narrow region around G_eff = 1/(10 MeV)^2. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. While we phrase our discussion here in terms of a specific scenario in which a late onset of neutrino free-streaming could occur, our constraints on the neutrino visibility function are very general.",
      "comment": "6 Pages, 3 figures, 1 table. Comments are welcome",
      "journal": null,
      "doi": null
    },
    {
      "version": "v2",
      "updated": "2014-12-06T19:16:37.000Z"
    }
  ],
  "analyses": {
    "subjects": [
      "98.80.Cq",
      "14.60.St",
      "98.70.Vc"
    ],
    "keywords": [
      "early universe",
      "neutrino-neutrino scattering",
      "conventional lambdacdm parameters cosmological data",
      "neutrino free-streaming",
      "neutrino sector"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1103/PhysRevD.90.123533",
      "journal": "Physical Review D",
      "year": 2014,
      "month": "Dec",
      "volume": 90,
      "number": 12,
      "pages": 123533
    },
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1237609,
      "adsabs": "2014PhRvD..90l3533C"
    }
  }
}