{"id":"80f2aa2c-fa3f-4c17-98a2-d3a8e342ad58","arxiv_id":"2607.07348","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":5,"one_line_summary":"DESI BAO+CMB yielding a positive present-day deceleration parameter q0≈0.10 (vs SDSS's q0≈−0.22) is explained by DESI's higher lowest effective redshift (0.295 vs 0.15), not by new physics.","lead":"This paper compares DESI and SDSS BAO data and finds that DESI's higher lowest-redshift bin (z_eff≈0.295 vs SDSS's 0.15) explains why DESI+CMB alone yields a positive (decelerating) q0, while SDSS+CMB yields a negative q0. The result matters because it suggests the apparent non-acceleration signal is a redshift-sampling artifact, not new physics, and recommends finer tomographic binning of DESI's Bright Galaxy Survey.","discovery_kind":"unclear","skeptic_critique":{"model":"glm-5.2","headline":"The SDSS-vs-DESI q0 comparison is confounded by mismatched CMB likelihoods, lensing data, and RSD inclusion; the publicly available BAO-only SDSS chains would isolate the geometric contribution but are not used.","rationale":"The reader correctly identified the most load-bearing concern: the comparison between DESI and SDSS chains is not apples-to-apples, and the confounds (especially RSD inclusion) could contribute to the q0 shift that the paper attributes to redshift sampling. The paper is commendably honest about these limitations — it explicitly names the BAO-only SDSS chains as a 'cheaper intermediate check' and frames its conclusions as 'directional' rather than definitive. This honesty justifies a CONDITIONAL verdict rather than REJECT.\n\nHowever, the omission of the BAO-only check is notable because the required chains are publicly available and the analysis is a straightforward posterior extraction. The RSD confound is particularly relevant for the CPL model because growth information constrains wa, which is correlated with w0 and thus q0. The MGS-removal test, while suggestive, cannot disentangle the redshift-sampling effect from the RSD/likelihood effects because it retains the SDSS pipeline's CMB and RSD choices.\n\nThe paper's two supporting tests (Pantheon+ addition and MGS removal) are internally consistent with the redshift-sampling hypothesis but are not sufficient to isolate it from the pipeline confounds. The Pantheon+ test shows that low-z information matters but does not distinguish between BAO redshift coverage and other systematic differences. The MGS-removal test moves in the right direction but undershoots the DESI value, with the residual unexplained in a controlled way.\n\nThe verdict should remain CONDITIONAL. The paper makes a physically motivated and plausible argument, but the central claim — that the q0 difference reflects redshift sampling 'rather than new physics' — is not yet established because the confounded comparison leaves open the possibility that pipeline differences contribute non-negligibly. The BAO-only SDSS chain check, which the paper itself proposes but does not perform, would be the single most informative next step.","tokens_in":22228,"tokens_out":3109,"duration_ms":201070,"concrete_test":"Download the publicly available BAO-only (no-RSD) SDSS DR16 chains from the same repository (the `base_w_wa_CMBLens_BAO` variant) and extract q0 from the w0waCDM posterior. Compare this BAO-only SDSS q0 to the full BAO+RSD SDSS q0=-0.22. If the BAO-only value shifts upward toward the DESI q0=+0.10 by more than ~0.1, then a non-negligible fraction of the SDSS–DESI q0 difference is attributable to RSD inclusion rather than redshift sampling, weakening the paper's central attribution. If the BAO-only SDSS q0 remains near -0.22, the redshift-sampling interpretation is strengthened.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim attributes the q0 difference between DESI+Planck (q0=+0.10) and SDSS+Planck (q0=-0.22) to redshift sampling alone. However, the two sets of chains differ in three ways beyond BAO redshift coverage: (1) CMB high-ℓ likelihood (Plik TTTEEE lite for SDSS vs NPIPE CamSpec for DESI), (2) lensing reconstruction (Planck 2018 vs Planck+ACT DR6), and (3) RSD inclusion (SDSS chains include growth information via `base_w_wa_CMBLens_BAORSD`; DESI BAO chains do not). The authors acknowledge all three in the Sec. 4 caveat and even note that BAO-only SDSS chains are publicly available as 'a cheaper intermediate check,' but state 'We attempt neither here.'\n\nThe RSD confound is the most concerning for the CPL model specifically. RSD constrains fσ8, which depends on the integrated growth history and thus on w(z) — including wa. In the w0–wa plane, RSD information can shift the posterior along the degeneracy direction, indirectly moving w0 and therefore q0. This means part of the SDSS–DESI q0 offset could arise from the extra growth constraints in SDSS rather than from the BAO redshift anchor. The MGS-removal test (Sec. 6.2.3) does not resolve this: it removes the low-z BAO anchor but retains RSD and the 2018-era CMB likelihood, so the residual offset between MGS-removed SDSS (q0=-0.10) and DESI (q0=+0.10) could be entirely due to these pipeline differences rather than 'remaining differences in redshift sampling and survey geometry' as the authors suggest. The ~1.1σ significance of the DESI–SDSS difference is also computed under an independence assumption that is complicated by the non-identical CMB inputs, making the tension quantification itself uncertain.","agreement_with_reader":"agree"},"referee_report":{"model":"glm-5.2","summary":"This manuscript compares the inference of the present-day deceleration parameter q0 from SDSS DR16 and DESI DR2 BAO data, both combined with Planck CMB, within the CPL (w0wa) dark energy parametrization. The central observation is that Planck+DESI yields q0 = +0.10 (median on the decelerating side), while Planck+SDSS yields q0 = -0.22 (accelerating). The authors attribute this difference to the gap in lowest effective redshift probed (z_eff ≈ 0.295 for DESI BGS vs. z_eff ≈ 0.15 for SDSS MGS), arguing that the DESI result reflects extrapolation rather than new physics. Two tests support this: adding Pantheon+ to DESI restores q0 ≈ -0.37, and removing the MGS anchor from SDSS shifts q0 from -0.22 toward -0.10. The paper concludes with a recommendation for finer tomographic binning of the DESI BGS sample.","tokens_in":22546,"tokens_out":1549,"duration_ms":340132,"significance":"The paper addresses a timely question: whether the DESI BAO+CMB hint of a non-accelerating present epoch is physically meaningful or an artifact of redshift sampling. The use of the parameter-free identity q0 = 1/2 Omega_m + 1/2(1+3w0)Omega_DE (Eq. 11) to compute q0 from MCMC posteriors is methodologically sound and avoids circularity. The two confirmatory tests (Pantheon+ addition, MGS removal) are well-designed and behave as predicted. The recommendation for finer BGS tomography is a concrete, falsifiable proposal. However, the quantitative force of the comparison is limited by acknowledged pipeline mismatches between the SDSS and DESI chains.","major_comments":[{"comment":"§4, caveat paragraph and §6.2.3: The SDSS chains (base_w_wa_CMBLens_BAORSD) include RSD (growth) information, while the DESI BAO chains do not. In the CPL model, RSD constrains fσ8, which depends on the integrated growth history and thus on w(z) including wa. This can shift the posterior along the w0–wa degeneracy direction, indirectly moving w0 and therefore q0. The MGS-removal test (§6.2.3) removes the low-z BAO anchor but retains RSD and the 2018-era CMB likelihood, so the residual offset between MGS-removed SDSS (q0 = -0.10) and DESI (q0 = +0.10) could be partly or entirely due to RSD and pipeline differences rather than 'remaining differences in redshift sampling and survey geometry' as stated. The authors note that BAO-only SDSS chains are publicly available and would isolate the geometric contribution, but state 'We attempt neither here.' This is the single most important gap: the","section":null},{"comment":"§5.1, Eqs. (14)–(15): The w0 offset between SDSS and DESI is ~0.30, corresponding to only ~1.1σ when treated as independent. The authors acknowledge this is 'a marginal, not a decisive, difference' and correctly note that shared Planck information makes the posteriors positively correlated, so 1.1σ is conservative. However, the abstract and conclusions frame q0 = +0.10 vs. q0 = -0.22 as a 'qualitative discrepancy' and a 'key result.' Given that both intervals are consistent with q0 = 0 at roughly 1σ, the framing overstates the statistical significance of the contrast. The paper should more clearly state in the abstract and conclusions that the difference is ~1.1σ and that the 'qualitative' framing refers to the sign of the median, not to a statistically significant tension.","section":null},{"comment":"§4.1 vs. §4.4: The Planck-only chains use Plik TTTEEE lite + 2018 lensing, the DESI chains use NPIPE CamSpec + Planck/ACT DR6 lensing, and the SDSS chains use 2018-era likelihoods. The authors state these differences are 'subdominant' but provide no quantitative justification. Even a rough estimate of the expected q0 shift from switching CMB likelihoods (e.g., comparing Planck-only results under Plik vs. NPIPE) would strengthen the claim that the BAO redshift coverage is the dominant driver. Without this, the attribution to redshift sampling alone remains unquantified.","section":null}],"minor_comments":[{"comment":"Table 1: The Planck-only wCDM row reports w0 = -1.59 and q0 = -1.44, which are far from ΛCDM values. While the uncertainties are large, these median values seem extreme; a brief comment on why Planck-only wCDM prefers such a phantom-like value would help the reader.","section":null},{"comment":"§6.2.1: The double transition redshift z_crit = {0.08, 0.86} for Planck+DESI is noted as arising from 'near-tangency of q(z) with zero.' It would help to show q(z) crossing zero twice in Fig. 1 (right panel) or a dedicated inset, as this is a striking qualitative claim.","section":null},{"comment":"Fig. 2 caption: The caption states the accelerating region is 'to the left of the curve' (more negative w0), but the q0 = 0 boundary (Eq. 12) has w0 = -1/(3Ω_DE), which becomes more negative as Ω_DE decreases. A reader might find it confusing which direction is 'left'; consider labeling the regions directly on the figure.","section":null},{"comment":"§6.2.3, Eq. (19): The MGS-removed SDSS result has q0 = -0.10 ± 0.33/0.35, which is consistent with both DESI's q0 = +0.10 and the full SDSS q0 = -0.22. The text describes this as 'intermediate,' which is true for the median, but the uncertainty is so large that the test is only weakly constraining. This should be stated more explicitly.","section":null},{"comment":"The reference list includes several 2026-dated arXiv entries (e.g., Ref. [17, 18, 41, 75]); ensure these are correctly cited and that journal references are finalized where applicable.","section":null},{"comment":"§3, Eq. (10): The notation switches between Ω_DE and Ω_DE,0; consider standardizing to one form throughout.","section":null}],"recommendation":"major_revision","confidential_remarks":"The core idea is sound and the paper is well-written, but the central comparison is confounded by pipeline differences that the authors acknowledge but do not control for. The BAO-only SDSS chains are publicly available and would directly test whether the q0 shift is geometric (redshift sampling) rather than driven by RSD or CMB likelihood differences. Running this comparison is feasible and would substantially strengthen (or weaken) the central claim. I would encourage the authors to perform this analysis in revision; without it, the attribution to redshift sampling alone is an assertion rather than a demonstrated result. The paper is appropriate in scope for the journal once this is addressed."},"author_rebuttal":{"model":"glm-5.2","summary":"We thank the referee for a careful and constructive report. The referee raises three major points: (1) the SDSS chains include RSD information while the DESI chains do not, and a BAO-only SDSS comparison would isolate the geometric contribution; (2) the ~1.1σ statistical significance of the w0 and q0 differences is understated in the abstract and conclusions; and (3) the claim that CMB likelihood differences are subdominant lacks quantitative justification. We address each point below and describe the revisions we will make.","responses":[{"response":"The referee is correct that the inclusion of RSD in the SDSS chains and its absence from the DESI BAO chains is a confounding factor, and that the BAO-only SDSS chains would provide a cleaner comparison. We agree this is the most important methodological gap in the current manuscript. We will address it in revision by running the BAO-only (no-RSD) SDSS DR16 chains, which are publicly available in the same repository we already use, and reporting the resulting q0 and w0 values alongside the existing results. This will directly isolate the geometric BAO contribution and allow us to assess how much of the SDSS–DESI offset persists when RSD is removed from the SDSS side. We will revise the manuscript accordingly, including updating Table 1 and the discussion in §6.2.3. We acknowledge that even after removing RSD, the CMB likelihood differences (Plik vs. NPIPE CamSpec, 2018 lensing vs. Planck+ACT DR6 lensing) will remain as a residual confounder; we address this in our response to the third comment below. We will also revise the language in §6.2.3 to avoid attributing the residual offset solely to 'remaining differences in redshift sampling and survey geometry' and will instead enumerate the RSD and CMB pipeline differences as additional possible contributors.","revision_made":"yes","referee_comment":"§4, caveat paragraph and §6.2.3: The SDSS chains include RSD (growth) information while DESI BAO chains do not. RSD constrains fσ8, which depends on the integrated growth history and thus on w(z) including wa, potentially shifting the posterior along the w0–wa degeneracy direction. The MGS-removal test retains RSD and 2018-era CMB, so the residual offset between MGS-removed SDSS (q0 = -0.10) and DESI (q0 = +0.10) could be partly or entirely due to RSD and pipeline differences. The BAO-only SDSS chains are publicly available and would isolate the geometric contribution, but the authors state 'We attempt neither here.' This is the single most important gap."},{"response":"The referee is correct. The ~1.1σ significance of the w0 (and q0) offset is already stated in §5.1, but the abstract and conclusions do not convey this clearly enough and could be read as implying a statistically significant tension. We will revise the abstract to explicitly note that the w0 and q0 differences correspond to approximately 1.1σ and that the 'qualitative discrepancy' refers to the sign of the posterior median (one positive, one negative), not to a statistically significant tension. We will make the corresponding revision in the conclusions (§7). The core argument of the paper—that the sign of the median q0 is sensitive to the lowest effective redshift probed, and that this sensitivity is demonstrated by the Pantheon+ addition and MGS-removal tests—does not depend on the difference being statistically significant, so this revision does not undermine the paper's thesis. Rather, it clarifies that we are reporting a directional trend supported by two confirmatory tests, not a detection of tension.","revision_made":"yes","referee_comment":"§5.1, Eqs. (14)–(15): The w0 offset between SDSS and DESI is ~0.30, corresponding to only ~1.1σ when treated as independent. The abstract and conclusions frame q0 = +0.10 vs. q0 = -0.22 as a 'qualitative discrepancy' and a 'key result.' Given that both intervals are consistent with q0 = 0 at roughly 1σ, the framing overstates the statistical significance of the contrast. The paper should more clearly state in the abstract and conclusions that the difference is ~1.1σ and that the 'qualitative' framing refers to the sign of the median, not to a statistically significant tension."},{"response":"The referee is right that the claim that CMB likelihood differences are 'subdominant' is currently unsupported by any quantitative estimate. We can partially address this: our independently run Planck-only chains (§4.1, Table 1) use Plik TTTEEE lite + 2018 lensing and yield q0 = -0.83 with very broad uncertainties in CPL. The DESI collaboration's own Planck-only chains using NPIPE CamSpec + Planck/ACT DR6 lensing are publicly available, and we can compute q0 from them using the same identity (Eq. 11). Comparing these two Planck-only results would give a direct, if rough, estimate of the q0 shift attributable to the CMB likelihood and lensing change alone. We will add this comparison to the revised manuscript. However, we want to be transparent about a limitation: because the Planck-only posteriors in CPL are extremely broad (the q0 uncertainty is ~0.8), the shift between Plik and NPIPE CamSpec may itself be poorly determined, and we may not be able to make a precise statement about its magnitude. If the shift is small compared to the BAO-driven shift (as we expect but must verify), this will support our argument; if it is not, we will revise our claim accordingly. In either case, we will remove the unsupported word 'subdominant' and replace it with the quantitative comparison.","revision_made":"partial","referee_comment":"§4.1 vs. §4.4: The Planck-only chains use Plik TTTEEE lite + 2018 lensing, the DESI chains use NPIPE CamSpec + Planck/ACT DR6 lensing, and the SDSS chains use 2018-era likelihoods. The authors state these differences are 'subdominant' but provide no quantitative justification. Even a rough estimate of the expected q0 shift from switching CMB likelihoods would strengthen the claim that BAO redshift coverage is the dominant driver."}],"tokens_in":22258,"tokens_out":1562,"duration_ms":198966,"standing_objections":["We cannot fully eliminate the CMB likelihood confounding without re-running all chains with a single, matched CMB+lensing likelihood. Our Planck-only chains use Plik + 2018 lensing, while the DESI public chains use NPIPE CamSpec + Planck/ACT DR6 lensing, and the SDSS public chains use 2018-era likelihoods. Re-running the SDSS or DESI BAO with a matched CMB pipeline is beyond the scope of what we can accomplish with publicly released chains alone. The BAO-only SDSS comparison (committed to in response to comment 1) and the Planck-only Plik-vs-NPIPE comparison (committed to in response to comment 3) will reduce but not eliminate this confounding. We will be transparent about this residual limitation in the revised manuscript."]},"desk_editor":{"model":"glm-5.2","letter":"The main thing to know: this paper argues that DESI BAO+CMB giving q0 > 0 (no present-day acceleration) is a redshift-sampling artifact, not new physics. The core idea is simple and correct — w0 and q0 are present-day quantities, and without a BAO anchor below z ~ 0.3, the CPL extrapolation drifts. The two confirmatory tests are the real contribution: adding Pantheon+ to DESI pulls q0 back to -0.37, and removing SDSS's low-z MGS anchor pushes SDSS's q0 from -0.22 toward -0.10. Both behave as the redshift-coverage hypothesis predicts. The MGS-removal test is the genuinely new piece — it's a clean demonstration that the low-z anchor matters, done within the same survey's chains rather than across surveys. The paper is also appropriately careful about scope: it explicitly says this explains the q0 anomaly in BAO+CMB only, not the full w0wa preference when supernovae are included. That distinction matters and they get it right. The q0 = (1/2)Ωm + (1/2)(1+3w0)ΩDE identity is parameter-free, so there's no circularity in deriving q0 from posteriors. Where the paper is soft is the cross-survey comparison itself. The SDSS and DESI chains differ in three ways beyond BAO redshift coverage: CMB high-ℓ likelihood (Plik vs NPIPE CamSpec), lensing (Planck 2018 vs Planck+ACT DR6), and RSD inclusion (SDSS chains include growth information, DESI BAO chains don't). The authors acknowledge all three in Section 4 and explicitly say they don't attempt the BAO-only SDSS check that would isolate the geometric contribution. The RSD confound is the most concerning for CPL specifically — RSD constrains fσ8, which depends on the integrated growth history and thus on wa, so it can shift the w0–wa posterior along the degeneracy direction and indirectly move q0. The MGS-removal test doesn't resolve this because it keeps RSD and the 2018-era CMB likelihood. The residual offset between MGS-removed SDSS (q0 = -0.10) and DESI (q0 = +0.10) could be partly pipeline, not just survey geometry. The ~1.1σ significance of the DESI–SDSS difference is also computed under an independence assumption that overestimates the variance (shared CMB information partially cancels), so the tension is if anything understated — but the mismatched pipelines make even that number uncertain. The recommendation for finer BGS tomography is constructive but untested; no forecast is provided. This is a useful diagnostic paper for anyone working on the DESI dark energy debate. The central claim is directionally right and well-motivated, but it's not definitively established because the apples-to-apples comparison wasn't done. A matched-likelihood, BAO-only reanalysis would close the gap. I'd send it to a serious referee — the MGS-removal test and the q0 framing are worth publishing, but the referee should push hard on the pipeline confounds and ask whether the BAO-only SDSS chains (which the authors note are publicly available) can be used to tighten the claim.","headline":"DESI's positive q0 from BAO+CMB is likely a redshift-coverage artifact, but the comparison is confounded by mismatched pipelines","tokens_in":23161,"tokens_out":806,"would_cite":false,"duration_ms":64146,"reading_group":"no","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"glm-5.2","headline":"DESI's Non-Accelerating Universe May Be a Redshift Gap, Not New Physics","keywords":["cosmic acceleration","deceleration parameter","baryon acoustic oscillations","DESI","SDSS","dark energy","CPL parametrization","redshift sampling"],"falsifier":"If finer tomographic binning of DESI's Bright Galaxy Survey at z_eff ~ 0.18 does not pull q_0 back toward negative values, or if a matched-likelihood reanalysis (identical CMB, BAO-only, no RSD) eliminates the q_0 shift between surveys, the redshift-sampling explanation would be weakened or falsified.","tokens_in":22416,"feed_emoji":"🔭","tokens_out":1289,"duration_ms":118111,"temperature":0.7,"pith_summary":"This paper argues that the apparent preference of DESI DR2 baryon acoustic oscillation data, when combined with CMB measurements, for a presently non-accelerating Universe is not evidence for exotic dark energy but a consequence of redshift sampling. DESI's lowest effective redshift bin sits at z_eff ≈ 0.295, while SDSS reaches down to z_eff ≈ 0.15. Because the present-day equation of state w_0 and the deceleration parameter q_0 are quantities defined at z = 0, the absence of a distance anchor close to the present epoch forces the CPL dark energy parametrization to extrapolate, allowing w_0 to drift toward zero and q_0 to become positive. The authors support this with two tests: adding Pantheon+ supernovae (which reach lower redshifts) to DESI restores q_0 to −0.37, and removing SDSS's low-redshift anchor shifts SDSS's q_0 from −0.22 toward −0.10, intermediate between the two surveys. They propose finer tomographic binning of DESI's Bright Galaxy Survey to access lower effective redshifts and test the conclusion.","feed_headline":"DESI's Non-Accelerating Universe May Be a Redshift Gap, Not New Physics","feed_subtitle":"The apparent loss of cosmic acceleration in DESI data stems from its lowest redshift bin sitting too high, forcing extrapolation to the","key_machinery":"The deceleration parameter q_0 = (1/2)Ω_m + (1/2)(1 + 3w_0)Ω_DE, which depends only on the present-day equation of state w_0 and energy densities. Within the CPL parametrization, w_0 is the parameter most directly tied to the lowest-redshift expansion history. A distance anchor at z_eff ≈ 0.15 constrains w_0 directly; an anchor at z_eff ≈ 0.295 forces extrapolation to z = 0, allowing w_0 to drift toward zero and pushing q_0 across the acceleration boundary.","core_discovery":"The discrepancy between DESI and SDSS on whether the Universe is currently accelerating is driven by the ~0.15 difference in their lowest effective redshift anchors (z_eff ≈ 0.295 for DESI vs. z_eff ≈ 0.15 for SDSS). In the CPL parametrization, w_0 and q_0 are present-day quantities that require low-redshift data to constrain directly; without such an anchor, the reconstruction extrapolates and q_0 drifts positive. Two tests confirm this: adding Pantheon+ supernovae to DESI restores acceleration (q_0 = −0.37), and removing SDSS's low-z MGS anchor shifts SDSS's q_0 from −0.22 toward −0.10.","pith_inferences":["The argument implies that the choice of dark energy parametrization itself matters: CPL extrapolates differently from, say, early dark energy or thawing quintessence models. A parametrization that changes more slowly at low redshift might show a smaller q_0 shift, suggesting the 'non-accelerating' result is partly an artifact of how CPL extrapolates into the unconstrained region.","The same redshift-coverage logic could apply to other present-day cosmological quantities derived from BAO+CMB combinations, such as H_0 or σ_8, potentially explaining other apparent tensions between DESI and earlier surveys.","If the proposed BGS tomographic split fails to restore acceleration, this would weaken the redshift-sampling explanation and reopen the possibility that the DESI BAO+CMB preference genuinely reflects the expansion history rather than an extrapolation artifact."],"forward_implications":["If finer tomographic binning of DESI's Bright Galaxy Survey can achieve an effective redshift of ~0.18, it would provide a direct test: a low-z BGS bin should pull q_0 back toward negative values, consistent with SDSS and ΛCDM.","The result suggests that the significance of dynamical dark energy claims from BAO+CMB combinations without low-redshift supernova anchors should be treated cautiously, as they depend on extrapolation within the chosen parametrization.","The finding motivates a matched-likelihood reanalysis (identical CMB likelihoods, BAO-only without RSD) to isolate the pure geometric contribution of redshift coverage versus other dataset differences.","If the redshift-sampling explanation is correct, future DESI data releases with finer low-z binning should show reduced tension with ΛCDM in the w_0–q_0 plane even without supernovae."],"fun_headline_variants":["DESI's Missing Cosmic Acceleration Tied to Low-Redshift Gap","Redshift Coverage, Not New Physics, Drives DESI Dark Energy Tension","DESI vs SDSS: Cosmic Acceleration Discrepancy Is a Sampling Artifact","Lower Redshift Anchor Restores Cosmic Acceleration in DESI Data","DESI's Non-Accelerating Universe Traced to Redshift Extrapolation"],"cache_read_input_tokens":0,"weakest_assumption_plain":"The comparison between DESI and SDSS chains is not apples-to-apples: the CMB likelihood versions differ (Plik vs. NPIPE CamSpec), the lensing datasets differ (Planck 2018 vs. Planck+ACT DR6), and the SDSS chains include redshift-space distortion (growth) information while the DESI BAO chains do not. The authors acknowledge this but attribute the q_0 shift to redshift coverage; if these dataset differences contribute non-negligibly, the redshift-sampling explanation is overst.","fun_headline_variants_meta":{"raw":{"variants":["DESI's Missing Cosmic Acceleration Tied to Low-Redshift Gap","Redshift Coverage, Not New Physics, Drives DESI Dark Energy Tension","DESI vs SDSS: Cosmic Acceleration Discrepancy Is a Sampling Artifact","Lower Redshift Anchor Restores Cosmic Acceleration in DESI Data","DESI's Non-Accelerating Universe Traced to Redshift Extrapolation"]},"model":"glm-5.2","effort":"low","cost_usd":0.0,"raw_usage":{"total_tokens":1031,"prompt_tokens":928,"completion_tokens":103,"prompt_tokens_details":null},"tokens_in":928,"tokens_out":103,"duration_ms":43406,"temperature":1.0,"reasoning_tokens":null,"cache_read_input_tokens":0,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-09T13:27:41.306787+00:00","model_set":{"reader":"glm-5.2"},"falsifier":"If finer tomographic binning of DESI's Bright Galaxy Survey at z_eff ~ 0.18 does not pull q_0 back toward negative values, or if a matched-likelihood reanalysis (identical CMB, BAO-only, no RSD) eliminates the q_0 shift between surveys, the redshift-sampling explanation would be weakened or falsified.","supporting_citations":[],"review_version":1}