{
  "id": "1507.08672",
  "version": "v1",
  "published": "2015-07-30T20:12:35.000Z",
  "updated": "2015-07-30T20:12:35.000Z",
  "title": "$K\\toπν\\barν$ and $ε'/ε$ in Simplified New Physics Models",
  "authors": [
    "Andrzej J. Buras",
    "Dario Buttazzo",
    "Robert Knegjens"
  ],
  "comment": "31 pages, 6 figures, 1 table",
  "categories": [
    "hep-ph",
    "hep-ex",
    "hep-lat"
  ],
  "abstract": "The decays $K^+\\to\\pi^+\\nu\\bar\\nu$ and $K_L\\to\\pi^0\\nu\\bar\\nu$, being the theoretically cleanest rare decays of mesons, are very sensitive probes of New Physics. In view of the excellent prospects of reaching the Standard Model sensitivity for $K^+\\to\\pi^+\\nu\\bar\\nu$ by the NA62 experiment at CERN and for $K_L\\to\\pi^0\\nu\\bar\\nu$ by the KOTO experiment at J-PARC, we study them in the simplest extensions of the SM in which stringent correlations between these two decays and other flavour observables are present. We first consider simple models with tree-level Z and Z' contributions in which either MFV or a $U(2)^3$ symmetry is imposed on the quark flavour-violating couplings. We then compare the resulting correlations with those present in generic models in which the latter couplings are arbitrary, subject to constraints from $\\Delta F=2$ processes, electroweak and collider data. Of particular interest are the correlations with $\\epsilon'/\\epsilon$ and $K_L\\to\\mu^+\\mu^-$ which limit the size of NP contributions to $K^+\\to\\pi^+\\nu\\bar\\nu$ and $K_L\\to\\pi^0\\nu\\bar\\nu$, depending on the Dirac structure of couplings and the relevant operators. But in MFV also the constraint from $B_s\\to\\mu^+\\mu^-$ turns out to be important. We take into account the recent results from lattice QCD and large N approach that indicate $\\epsilon'/\\epsilon$ in the SM to be significantly below the data. While in many models the enhancement of $\\epsilon'/\\epsilon$ implies a suppression of $K_L\\to\\pi^0\\nu\\bar\\nu$, we present two models in which these observables can be simultaneously enhanced relative to SM predictions. A correlation between $K^+\\to\\pi^+\\nu\\bar\\nu$ and $B\\to K(K^*)\\mu^+\\mu^-$, found by us in the simple models considered here, should be of interest for NA62 and LHCb experimentalists at CERN in the coming years. The one with $B\\to K(K^*)\\nu\\bar\\nu$ will be tested at Belle II.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-07-30T20:12:35.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "physics models",
      "correlation",
      "simple models",
      "theoretically cleanest rare decays",
      "standard model sensitivity"
    ],
    "publication": {
      "doi": "10.1007/JHEP11(2015)166",
      "journal": "Journal of High Energy Physics",
      "year": 2015,
      "month": "Nov",
      "volume": 2015,
      "pages": 166
    },
    "note": {
      "typesetting": "TeX",
      "pages": 31,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2015JHEP...11..166B",
      "inspire": 1385876
    }
  }
}