{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f047591564149ca27c85bdb88f85e7f23ceb33d524bb5e8f3140079568c80292","created":"2026-10-03T07:18:04Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"1a4d002ef70605ed9cfe1e518942cf76817e11afa0bbc559f62aac42ea5b40c4","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"grav.modified-gravity.well-posedness-mergers","kind":"well-posed","literature_status":"partially-resolved","n":"1","parents":[],"plain":"To simulate merging black holes in a modified theory, its equations must give a unique, stable evolution from given starting data. Some popular theories lose this property when gravity becomes strong.","posed_since":"","precise":"For Einstein-scalar-Gauss-Bonnet gravity, L = R/(16 pi G) - (1/2)(grad phi)^2 + alpha f(phi) $G_{\\mathrm{GB}}$ with G_GB the Gauss-Bonnet invariant, and for general Horndeski theories, strong hyperbolicity holds in modified harmonic gauge at weak coupling (Kovacs and Reall 2020). Determine the maximal coupling $\\alpha/M^2$ for which binary black hole evolutions stay strongly hyperbolic through merger, and whether effective-field-theory fixing of the equations converges to a unique answer as the fixing is removed. An answer is a theorem or convergent numerical evidence with the coupling threshold.","problem_ref":null,"references":"","settled_by":"Convergent merger simulations mapping the loss of hyperbolicity versus coupling, backed by a theorem on the fixing procedure.","status_note":"Well-posedness at weak coupling is proved (2020); simulations show loss of hyperbolicity at larger couplings, with theory-dependent thresholds.","title":"Are scalar-Gauss-Bonnet and higher-curvature theories well-posed in black hole 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