{
  "id": "2301.07226",
  "version": "v1",
  "published": "2023-01-17T23:49:58.000Z",
  "updated": "2023-01-17T23:49:58.000Z",
  "title": "The mass of charged pions in neutron star matter",
  "authors": [
    "Bryce Fore",
    "Norbert Kaiser",
    "Sanjay Reddy",
    "Neill C. Warrington"
  ],
  "comment": "13 pages, 4 figures, 1 appendix",
  "categories": [
    "nucl-th",
    "astro-ph.HE",
    "hep-ph"
  ],
  "abstract": "We examine the behavior of charged pions in neutron-rich matter using heavy-baryon chiral perturbation theory. This study is motivated by the prospect that pions, or pion-like, excitations, may be relevant in neutron-rich matter encountered in core-collapse supernovae and neutron star mergers. We find, as previously expected, that the $\\pi^-$ mass increases with density and precludes s-wave condensation, and the mass of the $\\pi^+$ mode decreases with increasing density. The energy difference between neutrons and protons in neutron-rich matter related to the nuclear symmetry energy alters the power counting. It enhances higher-order contributions to the pion self-energy. Previously unimportant but attractive diagrams are now enhanced. The net effect of this is the appearance of a new collective mode with the quantum numbers of the $\\pi^+$, and a pronounced reduction of the $\\pi^+$ mass.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-01-17T23:49:58.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "neutron star matter",
      "charged pions",
      "neutron-rich matter",
      "heavy-baryon chiral perturbation theory",
      "nuclear symmetry energy alters"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 13,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}