{"paper":{"title":"Quintessence-dominated cyclic universe with negative cosmological constant","license":"http://creativecommons.org/licenses/by/4.0/","headline":"A negative time-varying cosmological constant produces positive energy density and pressure sign flips in quintessence cyclic models.","cross_cats":["hep-th"],"primary_cat":"gr-qc","authors_text":"Kazuharu Bamba, Nasr Ahmed","submitted_at":"2025-12-15T21:23:37Z","abstract_excerpt":"We investigate two simplified non-singular cyclic models with a negative time-varying cosmological constant to represent the non-conventional mechanism of negative cosmological constant expected to address the late-time cosmic acceleration. We show that a physically acceptable evolution with positive energy density can be realized, while negative energy density dominates in case of a positive or zero cosmological constant. In the first model, we demonstrate a sign flipping of the cosmic pressure in a quintessence-dominated universe with no violation of the null energy condition. In the second "},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"We show that a physically acceptable evolution with positive energy density can be realized, while negative energy density dominates in case of a positive or zero cosmological constant. In the first model, we demonstrate a sign flipping of the cosmic pressure in a quintessence-dominated universe with no violation of the null energy condition.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The assumption that a negative time-varying cosmological constant can be introduced in a specific functional form that produces positive energy density and the desired cyclic behaviors without additional instabilities or contradictions with observations.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Two cyclic universe models with negative time-varying cosmological constant achieve positive energy density, pressure sign flip without null energy condition violation in quintessence domination, and phantom divide crossing in a matter-bounce scenario.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"A negative time-varying cosmological constant produces positive energy density and pressure sign flips in quintessence cyclic models.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"9243a9fb7e5c8393d01c05a3d1cecacab84c714929c478133cb82d7859ebb088"},"source":{"id":"2512.13906","kind":"arxiv","version":6},"verdict":{"id":"b64b64ee-7ef9-4d81-b93f-c3810470c939","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-16T21:31:02.624755Z","strongest_claim":"We show that a physically acceptable evolution with positive energy density can be realized, while negative energy density dominates in case of a positive or zero cosmological constant. In the first model, we demonstrate a sign flipping of the cosmic pressure in a quintessence-dominated universe with no violation of the null energy condition.","one_line_summary":"Two cyclic universe models with negative time-varying cosmological constant achieve positive energy density, pressure sign flip without null energy condition violation in quintessence domination, and phantom divide crossing in a matter-bounce scenario.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The assumption that a negative time-varying cosmological constant can be introduced in a specific functional form that produces positive energy density and the desired cyclic behaviors without additional instabilities or contradictions with observations.","pith_extraction_headline":"A negative time-varying cosmological constant produces positive energy density and pressure sign flips in quintessence cyclic models."},"integrity":{"clean":true,"summary":{"advisory":0,"critical":0,"by_detector":{},"informational":0},"endpoint":"/pith/2512.13906/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":2,"snapshot_sha256":"40bf99f711acf000c7168a78203a7526bc1fcdae96ac5dd0f7cf77e8a114310b"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}