{"paper":{"title":"Nonlinear hydrodynamics in spinning neutron stars: Theoretical universal relations and equilibrium solutions","license":"http://creativecommons.org/licenses/by-nc-sa/4.0/","headline":"","cross_cats":["astro-ph.HE"],"primary_cat":"gr-qc","authors_text":"Amlan Nanda, Fabian Gittins, Giorgio Nicolini, Hang Yu, K.J. Kwon, Nils Andersson, Pantelis Pnigouras, Shu Yan Lau, Tejaswi Venumadhav","submitted_at":"2026-07-08T21:42:21Z","abstract_excerpt":"We study tides during the inspiral of a binary neutron star (BNS) system, including nonlinear hydrodynamical interactions. Using an affine approximation that treats the perturbed NS as an ellipsoid, we analytically derive coupling coefficients among the f-modes and the radial mode to the four-wave order (i.e., next-to-next-to-leading order) in the Hamiltonian, allowing for arbitrary rotation of the background star. Our model reveals a series of universal relations from first-principles arguments. Besides the well-known relations, we show that the three-wave (next-to-leading-order) interaction "},"claims":{"count":0,"items":[],"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"source":{"id":"2607.07943","kind":"arxiv","version":1},"verdict":{"id":null,"model_set":{},"created_at":null,"strongest_claim":"","one_line_summary":"","pipeline_version":null,"weakest_assumption":"","pith_extraction_headline":""},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2607.07943/integrity.json","findings":[],"available":true,"detectors_run":[],"snapshot_sha256":"c28c3603d3b5d939e8dc4c7e95fa8dfce3d595e45f758748cecf8e644a296938"},"references":{"count":0,"sample":[],"resolved_work":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}