{
  "id": "hep-ph/9910216",
  "version": "v1",
  "published": "1999-10-04T08:48:32.000Z",
  "updated": "1999-10-04T08:48:32.000Z",
  "title": "Chiral symmetry breaking and instantons in both quenched and full QCD",
  "authors": [
    "U. Sharan",
    "M. Teper"
  ],
  "comment": "72 pages, revtex",
  "categories": [
    "hep-ph",
    "hep-lat",
    "hep-th"
  ],
  "abstract": "We investigate the contribution that instantons make to the QCD chiral condensate for Nf= 0, 1 and 2 quark flavours. We use a simplified model: the instantons are a (weighted) gas, the fermionic integrations are restricted to the subspace spanned by the would-be zero-modes and only the dimensional and chiral features of the Dirac operator are retained. Previous work along these lines found a power-like divergence of the Dirac spectral density at zero eigenvalue. By changing the various components of the model, we show that a power divergence appears to be a generic feature of instanton mixing for both Nf=0 and Nf=/=0. In the latter case the divergence disappears as m->0 in such a way that psibar-psi remains finite. We find that the exponent of the power decreases for larger instanton densities, becoming negligible for very dense instanton `gases'. We reproduce the expected m-dependence of the topological susceptibility, we investigate the space-time structure of the eigenfunctions, as a function of the eigenvalue, and we calculate the eta-prime mass. In summary: instantons appear to provide a natural mechanism for the spontaneous breaking of chiral symmetry in QCD, but they typically produce a power-like divergence in the Dirac spectral density. This divergence is non-standard but `harmless' in the case of full QCD, and implies a pathology in the case of quenched QCD.",
  "revisions": [
    {
      "version": "v1",
      "updated": "1999-10-04T08:48:32.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "chiral symmetry breaking",
      "full qcd",
      "dirac spectral density",
      "qcd chiral condensate",
      "larger instanton densities"
    ],
    "note": {
      "typesetting": "RevTeX",
      "pages": 72,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 508095,
      "adsabs": "1999hep.ph...10216S"
    }
  }
}