{
  "abstract": "We present an implementation of an HLLD approximate Riemann solver for the AthenaK astrophysics code with support for full general relativistic magnetohydrodynamics via a tetrad frame transformation. Our implementation uses an initial guess for the HLLD iterative solve which eliminates the need for an additional conserved-to-primitive inversion, which greatly accelerates performance without affecting accuracy. Additionally, by coupling the method with a first-order flux correction, we are able to use the method reliably even when the magnetization exceeds $10^4$, which we achieve in a SANE accretion disk. Our SANE disk shows that HLLD leads to a more strongly magnetized funnel and more accurate horizon fluxes when compared with HLLE. We further apply the new HLLD implementation to an equal-mass binary neutron star merger. For our long-lived remnant, HLLD enhances the magnetic shear stresses in the outer layers and leads to weaker differential rotation. However, due to weaker gravitational wave emissions in the post-merger phase, the remnant is consistently less compact while producing more dynamical ejecta and a more massive disk. The cost of this new solver is relatively modest thanks to the improved initial guess: our accretion disk tests are only ${\\sim}10-25\\%$ slower than HLLE, and for our binary neutron star runs with a microphysical equation of state, we find that HLLD is only ${\\sim}3\\%$ slower than HLLE across all runs.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.06150",
  "author_total": 3,
  "authors": [
    {
      "name": "Jacob Fields"
    },
    {
      "name": "George N. Wong"
    },
    {
      "name": "James M. Stone"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3739cbhtgs59g.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.06150",
  "fulltext_url": null,
  "id": "3739cbhtgs59g",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.06150",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "arxiv",
      "gr-qc"
    ],
    [
      "openalex",
      "2206|Computational Fluid Dynamics and Aerodynamics"
    ]
  ],
  "openalex": "W7212024374",
  "pdf_url": "https://arxiv.org/pdf/2609.06150",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-05",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3739cbhtgs59g.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:19:48Z",
      "native_id": "2609.06150",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.06150"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "physics",
      "origin": "arxiv:gr-qc",
      "subfield": "gravitation"
    }
  ],
  "title": "An HLLD Implementation for General Relativistic Magnetohydrodynamics in AthenaK",
  "title_text": "An HLLD Implementation for General Relativistic Magnetohydrodynamics in AthenaK",
  "type": "preprint",
  "updated_at": "2026-10-30T12:19:48Z",
  "url": "https://research.draconitic.com/paper/3739cbhtgs59g",
  "venue": "arXiv",
  "versions": []
}