{
  "id": "2207.13133",
  "version": "v1",
  "published": "2022-07-26T18:22:38.000Z",
  "updated": "2022-07-26T18:22:38.000Z",
  "title": "Probing Physics Beyond the Standard Model: Limits from BBN and the CMB Independently and Combined",
  "authors": [
    "Tsung-Han Yeh",
    "Jessie Shelton",
    "Keith A. Olive",
    "Brian D. Fields"
  ],
  "comment": "40 pages, 12 figures",
  "categories": [
    "astro-ph.CO",
    "hep-ph"
  ],
  "abstract": "We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number $N_\\nu$ of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates $d+d \\rightarrow He3 + n$ and $d+d \\rightarrow H3 + p$. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs $N_\\nu$ and $\\eta$ prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives $N_\\nu = 2.898 \\pm 0.141$, resulting in $N_\\nu < 3.180$ at $2\\sigma$. We apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. We also search for limits on potential {\\em changes} in $N_\\nu$ and/or the baryon-to-photon ratio $\\eta$ between the two epochs. The present data place strong constraints on the allowed changes in $N_\\nu$ between BBN and CMB decoupling; for example, we find $-0.708 < N_\\nu^{\\rm CMB}-N_\\nu^{\\rm BBN} < 0.328$ in the case where $\\eta$ and the primordial helium mass fraction $Y_p$ are unchanged between the two epochs; we also give limits on the allowed variations in $\\eta$ or in $(\\eta,N_\\nu)$ jointly. Looking to the future, we forecast the tightened precision for $N_\\nu$ arising from both CMB Stage 4 measurements as well as improvements in astronomical \\he4 measurements. We find that CMB-S4 combined with present BBN and light element observation precision can give $\\sigma(N_\\nu) \\simeq 0.03$. Such future precision would reveal the expected effect of neutrino heating ($N_{\\rm eff}-3=0.044$) of the CMB during BBN, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2022-07-26T18:22:38.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "standard model",
      "probing physics",
      "latest light element observations",
      "stochastic gravitational wave background",
      "data place strong constraints"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 40,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}