{
  "id": "1812.05157",
  "version": "v1",
  "published": "2018-12-12T21:18:07.000Z",
  "updated": "2018-12-12T21:18:07.000Z",
  "title": "Lepton Number and Expansion of the Universe",
  "authors": [
    "Cheng Tao Yang",
    "Jeremiah Birrell",
    "Johann Rafelski"
  ],
  "comment": "6 pages, 5 figures",
  "categories": [
    "hep-ph"
  ],
  "abstract": "We show that the non-integer effective number of neutrinos $N^{\\mathrm{eff}}_\\nu$ can be understood as an effect of lepton $L$ asymmetry in the early Universe carried by the Dirac neutrino cosmic background. We show that $N_\\nu^{\\mathrm{eff}}=3.36\\pm0.34$ (CMB only) and $N_\\nu^{\\mathrm{eff}}= 3.62\\pm0.25$ (CMB and $H_0$) require a ratio between baryon number $B$ and lepton number to be $1.16 \\times 10^{-9}\\leqslant B/|L|\\leqslant 1.51 \\times 10^{-9}$. These values are close to the baryon-to-photon ratio $0.57\\times 10^{-9}\\leqslant B/N_\\gamma \\leqslant 0.67\\times10^{-9}$. Thus instead of the usual $|L|\\ll N_\\gamma$ and $B\\simeq |L|$, we propose to use $0.4 \\leqslant |L|/N_\\gamma\\leqslant 0.52$ and $B\\ll|L|$ as another natural choice, which resolves the tension between Planck-CMB and $H_0$ and leads to a non-integer value of $N_\\nu^{\\mathrm{eff}}>3$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-12-12T21:18:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "lepton number",
      "dirac neutrino cosmic background",
      "natural choice",
      "baryon-to-photon ratio",
      "baryon number"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}