{"work":{"id":"4a81fb6a-447f-4143-95e4-aeeeb02c3c23","openalex_id":null,"doi":null,"arxiv_id":"2405.03933","raw_key":null,"title":"Assessing observational constraints on dark energy","authors":null,"authors_text":null,"year":2024,"venue":"astro-ph.CO","abstract":"Observational constraints on time-varying dark energy ({\\it e.g.}, quintessence) are commonly presented on a $w_0$-$w_a$ plot that assumes the equation of state of dark energy strictly satisfies $w(z)= w_0+ w_a z/(1+z)$ as a function of the redshift $z$. Recent observations favor a sector of the $w_0$-$w_a$ plane in which $w_0 > -1$ and $w_0+w_a< -1$, suggesting that the equation of state underwent a transition from violating the null energy condition (NEC) at large $z$ to obeying it at small $z$. In this paper, we demonstrate that this impression is misleading by showing that simple quintessence models satisfying the NEC for all $z$ predict an observational preference for the same sector. We also find that quintessence models that best fit observational data can predict a value for the dark energy equation of state at present that is significantly different from the best-fit value of $w_0$ obtained assuming the parameterization above. In addition, the analysis reveals an approximate degeneracy of the $w_0$-$w_a$ parameterization that explains the eccentricity and orientation of the likelihood contours presented in recent observational studies.","external_url":"https://arxiv.org/abs/2405.03933","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-23T04:07:30.638073+00:00","pith_arxiv_id":"2405.03933","created_at":"2026-05-11T09:56:03.576467+00:00","updated_at":"2026-06-05T21:23:00.469572+00:00","title_quality_ok":true,"display_title":"Assessing observational constraints on dark energy","render_title":"Assessing observational constraints on dark energy"},"hub":{"state":{"work_id":"4a81fb6a-447f-4143-95e4-aeeeb02c3c23","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":12,"external_cited_by_count":null,"distinct_field_count":2,"first_pith_cited_at":"2024-04-03T18:41:51+00:00","last_pith_cited_at":"2026-05-20T17:46:56+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-06-19T18:37:38.274639+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":8}],"polarity_counts":[{"context_polarity":"background","n":8}],"runs":{},"summary":{},"graph":{},"authors":[]}}