{"id":"4b3655ba-1a64-4cf1-a8c9-d54b7947b99a","arxiv_id":"2505.02658","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Using rotated BAO coordinates, DESI DR2 distance measurements are consistent with Planck LCDM, and the reported 3.1 sigma evidence for evolving dark energy is attributed to statistical methodology and prior choices.","lead":"Galaxy surveys measure an ancient ripple in galaxy positions called the baryon acoustic oscillation. A Cambridge cosmologist re-analyzes the DESI survey's BAO distances with two rotated quantities and concludes the newest data agree with the standard Planck model, with no strong evidence for evolving dark energy.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 'no evidence for evolving dark energy' conclusion is prior-dependent; the paper's own Delta-chi2=-8.0 and the LRG2 Dperp shift do not support the headline as stated.","rationale":"The rotated-coordinate construction in Sec. 2 (Eqs. 4-7) is a clear and useful tool, and the Dperp residual plots are a legitimate way to visualize BAO-CMB consistency under LCDM. The paper deserves credit for that. The soft spot is the leap from these LCDM-conditional consistency checks to the global statement that there is no significant evidence for evolving dark energy. That statement does not follow from the likelihood alone: the paper's own Delta-chi2_MAP = -8.0 for two extra parameters is a moderate improvement, and the posterior still allows wa about -1.8. The conclusion becomes 'no evidence' only after applying a prior penalty that the author describes as entirely subjective. The proposed Bayes-factor computation would settle whether any reasonable prior removes the preference; absent that calculation, the abstract overstates a prior-dependent judgment as an empirical result. The LRG2 Dperp shift in Table 1 is a secondary internal inconsistency in the 'unambiguously closer' language, but it does not change the overall verdict. The paper is best read as a conditional analysis: no-EvDE holds under a strong prior against dynamical dark energy, not as an unqualified finding.","tokens_in":13022,"tokens_out":14031,"duration_ms":167124,"concrete_test":"Compute the Bayesian evidence ratio for w0waCDM versus LCDM from the Sec. 3 DESI+QCMB chains, using at least two explicit priors on (w0, wa): (i) the uniform prior already used in the chains, and (ii) a Gaussian prior centered at (-1, 0) with width (0.5, 0.5). Report log-evidence and the implied posterior probability of LCDM in each case. If the evidence favors LCDM under both priors, the subjective-penalty concern is resolved; if it favors w0waCDM under the uniform prior, the 'no significant evidence' headline is prior-dependent and should be rephrased accordingly.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that DESI BAO + CMB show 'no significant evidence in support of evolving dark energy' is not forced by the likelihood. In Sec. 3 the author reports Delta-chi2_MAP = -8.0 for w0waCDM over LCDM for the DESI+QCMB combination, and then argues that evolving-dark-energy models should receive a large prior penalty, explicitly conceding 'How big a penalty is entirely subjective'. Because the CMB+BAO degeneracy direction in (w0, wa) is nearly parallel to the geometric degeneracy, the rotated pivot constraint w(z=0.5) = -0.996 +/- 0.046 does not by itself rule out evolution; the same posterior gives wa = -1.78 +/- 0.79, about 2.3 sigma from zero. Thus 'no significant evidence' is a prior-dependent judgment, not a model-independent empirical finding. A secondary internal tension: Table 1 shows LRG2 Dperp moving from 9.54 +/- 0.60 (DR1) to 8.76 +/- 0.34 (DR2) against Planck 9.22, with the p-value worsening from 0.60 to 0.16, so the Sec. 4 wording that DR2 'demonstrate unambiguously' moves closer is stronger than the tabulated values support.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes a rotated-coordinate analysis of DESI BAO distance measurements, defining orthogonal quantities D_perp and D_par from DM/rd and DH/rd. The author argues that, under Planck LCDM, D_perp is predicted with negligible uncertainty, allowing a clean consistency test of DESI DR1 and DR2 against Planck. The paper reports that DESI DR2 D_perp measurements are in better agreement with Planck LCDM than DR1, that D_par converts to constraints on omega_m that remain consistent with Planck, and that a rotated w0-wa analysis gives w(z=0.5) = -0.996 +/- 0.046. The paper further critiques the DESI collaboration's use of Delta-chi^2_MAP as evidence for evolving dark energy, arguing that the evidence is prior-dependent, and includes an appendix comparing DES5Y supernova constraints with DESI and Planck.","tokens_in":13312,"tokens_out":9290,"duration_ms":114850,"significance":"The D_perp statistic is a useful, transparent consistency test, and the analytic Gaussian marginalization is straightforward and reproducible from the quoted DESI and Planck results. The paper also makes a valid and important methodological point: Delta-chi^2_MAP with a uniform prior in (w0, wa) is not a model-independent measure of evidence for evolving dark energy. If the quantitative claims are brought in line with the tables, the rotated-coordinate framework could be a valuable addition to the BAO literature. However, the paper's headline statements currently outrun the tabulated results in a few places, and the omega_m conversion needs an error-propagation check.","major_comments":[{"comment":"The statement that the 2025 DESI data are 'more consistent with LCDM' for both LRG samples is not supported by Table 1. For LRG2, D_perp moves from 9.54 +/- 0.60 (DR1) to 8.76 +/- 0.34 (DR2), with the Planck value at 9.22; the absolute residual grows from 0.32 to 0.46 and the two-tailed p-value worsens from 0.60 to 0.16. The abstract and Section 4 should either restrict the 'moves closer' claim to LRG1 and to the full redshift set, or explicitly justify why the worsening LRG2 p-value is not the relevant comparison.","section":"Section 2 and Table 1"},{"comment":"The conclusion that there is 'no significant evidence in support of evolving dark energy' is prior-dependent rather than an empirical finding. The paper reports Delta-chi^2_MAP = -8.0 for w0waCDM relative to LCDM, and the rotated posterior gives wa = -1.78 +/- 0.79, about 2.3 sigma from zero; the conclusion relies on a subjective prior penalty whose size is conceded in the text to be 'entirely subjective.' The abstract and conclusions should state this conditionality explicitly, for example by saying 'under the Bayesian prior penalty adopted here.'","section":"Section 3 and Abstract"},{"comment":"The conversion of D_par measurements into omega_m constraints does not propagate the uncertainty in the slope beta or in the Planck reference value D_par^Planck. Table 2 lists Planck D_par uncertainties of order 0.1, which, when multiplied by beta ~ 0.009, contribute about 0.001 to omega_m, comparable to the quoted DESI omega_m errors of ~0.0015. The reported omega_m errors and the ~2.1 sigma average tension with Planck should be revised to include these terms, or the paper should justify that they are negligible.","section":"Section 2, Eq. (7), and Table 2"}],"minor_comments":[{"comment":"The caption describes red and blue contours as 'Pantheon+ (red) and DES5Y (blue) SN compilations,' but the text in Section 3 describes the red contours as DESI-DR2 BAO and DESI+QCMB; the caption should be corrected to match the text.","section":"Figure 4 caption"},{"comment":"The phrase 'as shown in the lower panel of Fig. 2' refers to the D_par results, but the lower panel of Fig. 3 contains the omega_m plot; the figure reference should be corrected.","section":"Section 4"},{"comment":"The table should state the sign convention for N_sigma; the listed values are consistent with N_sigma = (D_perp^Planck - D_perp^DESI)/sigma, but this is not stated explicitly in the caption.","section":"Table 1"},{"comment":"There are minor typographical errors, including 'perpendiclular' for 'perpendicular' and 'distrbution' for 'distribution,' which should be corrected in a revised version.","section":"Throughout"},{"comment":"The exponent is printed as -a11 + a12^2/(4a22); while this is algebraically correct after marginalization, the plus sign inside the exponent may confuse readers, so a one-line derivation or a clarifying note would help.","section":"Eq. (5)"}],"recommendation":"major_revision","confidential_remarks":"The D_perp consistency test is a genuinely useful addition, and the critique of Delta-chi^2_MAP is legitimate. The main issues are overstatement of the DR2 'moves closer' claim for LRG2, the prior-dependence of the no-evolution conclusion, and the missing error propagation in the omega_m conversion. These are fixable within the manuscript's scope, but they affect central claims and therefore warrant a major revision rather than a minor one."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this if you care about the DESI dark-energy debate. The genuinely new thing is the D_perp/D_par rotation. It converts the highly correlated DM/rd and DH/rd measurements into one direction that Planck pins to a near delta-function under ΛCDM, and one that tracks omega_m. That is a simple, useful diagnostic, and the DR1-to-DR2 comparison is a legitimate new result. The DR2 shifts are real: LRG1 D_perp tension drops from about 2.5σ to 1.8σ, and the higher-redshift points are all quiet. The D_par-to-omega_m mapping via Eq. 7 is transparent, and the agreement with Planck is striking.\n\nThe soft spots are in the interpretive layer. The headline claim that there is no significant evidence for evolving dark energy is not forced by the likelihood. The paper's own DESI+QCMB fit gives Δχ²_MAP = -8.0 for w0waCDM over ΛCDM, and after rotating to the pivot, the same posterior gives wa = -1.78 ± 0.79. The w(z=0.5) = -0.996 result is a reparameterization, not a model-independent ruling-out of evolution. The conclusion rests on choosing a large Bayesian prior penalty for EvDE models, and the paper says so explicitly. I agree the penalty is reasonable, but it is a judgment, and the abstract should not present it as a property of the data alone.\n\nAlso, the 'demonstrate unambiguously' wording is stronger than Table 1 supports. LRG2's D_perp p-value actually goes from 0.60 to 0.16 as the error bar shrinks; the central value moves closer to Planck, so the statement can be defended, but 'unambiguously' oversells the one point that got noisier. The beta calibration error in Eq. 7 appears not to be propagated; likely a small effect, but it should be checked. The decision to drop SN data is argued, but selective—the Appendix shows DES5Y tension, which is relevant, but the main text sidesteps the SN+DESI combination that drives the highest DESI significances.\n\nBottom line: the rotated-coordinate analysis deserves a serious referee and will be cited. The statistical critique of Δχ² as evidence is also worth having. But the paper's lasting value is the diagnostic, not the no-evidence conclusion, which is prior-dependent. If I were refereeing, I would ask for the abstract and conclusions to be softened, for the beta error to be propagated, and for the LRG2 wording to be calibrated to the actual numbers.","headline":"A clean rotated-coordinate diagnostic shows DESI DR2 BAO are more Planck-ΛCDM-friendly than DR1, but the paper's stronger 'no evidence for evolving dark energy' conclusion is a prior-dependent judgment, not an empirical fact.","tokens_in":13819,"tokens_out":1946,"would_cite":true,"duration_ms":22363,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["98.80.-k","95.36.+x"],"model":"deepseek-v4-flash","headline":"In rotated coordinates, DESI DR2 BAO data move into line with Planck ΛCDM; no significant evidence for evolving dark energy remains.","keywords":["baryon acoustic oscillations","dark energy equation of state","evolving dark energy","cosmological constant","DESI DR2","Planck ΛCDM","BAO distance ratios","Bayesian evidence"],"falsifier":"If a future BAO data set (e.g., DESI DR3) finds the LRG1 $D_{\\rm perp}$ value falling below its DR2 value of $5.08\\pm0.37$ and the pivot equation-of-state $w(z=0.5)$ moving more than about 2σ away from $-1$ in a joint BAO+CMB fit, the paper's conclusion that DR2 moved toward Planck ΛCDM with no evidence for evolving dark energy would be contradicted.","tokens_in":12823,"feed_emoji":"🌌","tokens_out":21525,"duration_ms":199576,"temperature":0.7,"pith_summary":"This paper claims that baryon acoustic oscillation (BAO) distance measurements from DESI's second data release, when rotated into a coordinate frame aligned with the predictions of the standard Planck ΛCDM model, are consistent with that model across the whole redshift range of the survey, and are substantially closer to it than the first DESI release was. In the orthogonal direction, the rotated variable gives a measure of the physical matter density that also remains consistent with Planck. The paper then applies the same rotation idea to the dark-energy equation-of-state parameters $w_0$ and $w_a$, finding that the combination of DESI BAO and CMB data constrains the pivot value $w(z=0.5) = -0.996 \\pm 0.046$, essentially the cosmological constant value. It concludes that there is no significant evidence for evolving dark energy in the present data, and argues that the DESI collaboration's higher significance claims rest on a statistical measure that fails to account for model complexity and prior assumptions.","feed_headline":"New DESI data fit standard cosmology, weakening dark-energy hint","feed_subtitle":"Rotating the galaxy-distance data shows DESI DR2 fits the standard cosmological model, weakening the dark-energy hint.","key_machinery":"The load-bearing object is a rotation of the two BAO observables $D_M/r_d$ and $D_H/r_d$ into orthogonal combinations $D_{\\rm perp}$ and $D_{\\rm par}$, with a rotation angle $\\gamma(z)$ chosen at each effective redshift so that the Planck ΛCDM degeneracy line (fixed by the tight constraint on $\\Omega_m h^3$) becomes horizontal. In this frame $D_{\\rm perp}$ is predicted by Planck with negligible error, so agreement with ΛCDM is settled by a single number with no nuisance parameters or priors, while $D_{\\rm par}$ maps linearly onto the physical matter density through $\\omega_m = 0.14205 + \\beta\\,(D_{\\rm par} - D_{\\rm par}^{\\rm Planck})$. A second rotation acts in theory space: replacing $(w_0, w_a)$ by $(w_{\\rm piv}, w_a)$ with $w_{\\rm piv} = w(z_{\\rm piv})$ at $z_{\\rm piv}\\approx 0.5$ decorrelates the two dark-energy parameters, showing that the pivot equation-of-state is tightly constrained and consistent with a cosmological constant.","core_discovery":"The central claim, stated on the paper's own terms, is that the DESI DR2 BAO measurements 'move closer towards the expectations of Planck ΛCDM' compared with DR1, and that from the comparison of Planck and DESI BAO measurements 'we find no significant evidence in support of evolving dark energy.' The analysis defines the two rotated distance ratios $D_{\\rm perp}$ and $D_{\\rm par}$, chosen so that Planck's ΛCDM prediction for $D_{\\rm perp}$ is essentially a delta function at every effective redshift. For the two low-redshift luminous-red-galaxy samples that showed the largest DR1 discrepancy, the $D_{\\rm perp}$ residuals shift from 2.5σ and -0.5σ in DR1 to 1.8σ and 1.4σ in DR2. The $D_{\\rm par}$ data translate into a matter density $\\omega_m = 0.13909 \\pm 0.00073$ averaged over all redshifts, about 2.1σ below the Planck value, and the extension to the $w_0$–$w_a$ parametrization yields $w(z=0.5) = -0.996 \\pm 0.046$ when DESI BAO and the compressed CMB likelihood are combined. The paper also shows that reparameterizing the dark-energy model to a pivot redshift decorrelates $w_0$ and $w_a$, exposing why the DESI collaboration's quoted significance, based on $\\Delta\\chi^2_{\\rm MAP}=-8.0$, overstates the case for evolving dark energy.","pith_inferences":["A direct test of the trend: if the DESI DR3 release finds the LRG1 $D_{\\rm perp}$ central value below its DR2 value of $5.08\\pm0.37$, the convergence toward Planck seen in DR2 would look like a statistical fluctuation rather than a systematic improvement.","The same rotation construction depends only on the Planck-ΛCDM degeneracy direction, so it can be applied unchanged to future BAO surveys to provide a near-model-free consistency check with the CMB.","If the paper's Bayesian-prior argument is right, the burden shifts to dark-energy model builders: to make a convincing case for evolving dark energy, the combined data would need to produce a much larger $\\Delta\\chi^2$ improvement than $-8$, or the field would need a principled theoretical prior for $w_0$–$w_a$ models.","The appendix's worsening DES5Y-versus-DESI/Planck tension suggests that the '4σ' claims quoted from combining DES5Y supernovae with DESI BAO are dominated by the supernova sample rather than by dark energy; recalibrating the DES5Y low-redshift photometry should remove or confirm that tension."],"forward_implications":["If the rotated-variable analysis is correct, DESI DR2 BAO data are consistent with the Planck ΛCDM cosmology at all effective redshifts from $z\\approx 0.5$ to $z\\approx 2.3$, with the two LRG samples that previously showed tension moving into line.","The matter density inferred from $D_{\\rm par}$, averaged over all DESI samples, is $\\omega_m = 0.13909 \\pm 0.00073$, about 2.1σ below Planck, implying mild tension remains only in the parallel direction.","In the $w_0$–$w_a$ extension, the pivot equation-of-state is $w(z=0.5) = -0.996 \\pm 0.046$, so the data are compatible with a cosmological constant at the pivot despite the large $w_a$ uncertainty.","The DESI team's '3.1σ' preference for evolving dark energy from DESI BAO + CMB is not a robust probability: it follows from $\\Delta\\chi^2_{\\rm MAP}=-8.0$ treated as a chi-squared statistic without a prior penalty, and the paper argues a physically motivated prior would eliminate the preference.","Adding alternative CMB data (ACT) does not strengthen the case for evolving dark energy, and some Planck+ACT combinations weaken it (as the paper cites from Garcia-Quintero et al. 2025)."],"supporting_citations":[{"why":"Supplies the DESI DR2 BAO measurements and the compressed CMB likelihood Q_CMB that the rotated-coordinate analysis is applied to.","marker":"DESI Collaboration et al. 2025"},{"why":"Provides the DESI DR1 BAO measurements that DR2 is compared against to show the shift toward Planck ΛCDM.","marker":"DESI Collaboration et al. 2024"},{"why":"Defines the reference ΛCDM cosmology and supplies the chains whose predictions for $D_{\\rm perp}$ and $D_{\\rm par}$ are the benchmark of the test.","marker":"Planck Collaboration et al. 2020"},{"why":"Establishes why Planck tightly constrains $\\Omega_m h^3$, the degeneracy-line reasoning that motivates the rotation angles $\\gamma(z)$.","marker":"Efstathiou & Gratton 2021"},{"why":"Shows that reparameterizing $(w_0, w_a)$ to a pivot equation-of-state decorrelates the parameters, the rotation used to display $w(z=0.5)$.","marker":"Cortês & Liddle 2024"},{"why":"Supplies the SDSS/BOSS BAO results that the paper says DESI DR2 has moved into closer agreement with.","marker":"Alam et al. 2017"}],"fun_headline_variants":["DESI DR2 fits Planck cosmology, dark energy hint fades","New BAO analysis: DESI data align with standard model","Rotated BAO distances: no sign of evolving dark energy","DESI DR2 vs Planck: dark energy evidence weakens","BAO angles reveal DESI data closer to Lambda CDM"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The central conclusion rests on a subjective prior that judges evolving-dark-energy models as much less plausible than the cosmological constant before the data are examined; the paper explicitly concedes that the size of this penalty is entirely subjective, and without it the DESI data improve the fit by $\\Delta\\chi^2 = -8.0$.","fun_headline_variants_meta":{"raw":{"variants":["DESI DR2 fits Planck cosmology, dark energy hint fades","New BAO analysis: DESI data align with standard model","Rotated BAO distances: no sign of evolving dark energy","DESI DR2 vs Planck: dark energy evidence weakens","BAO angles reveal DESI data closer to Lambda CDM"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000687,"raw_usage":{"total_tokens":3235,"prompt_tokens":1189,"completion_tokens":2046,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":805,"completion_tokens_details":{"reasoning_tokens":1959}},"tokens_in":805,"tokens_out":2046,"duration_ms":13988,"temperature":1.0,"reasoning_tokens":1959,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T00:44:56.644745+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If a future BAO data set (e.g., DESI DR3) finds the LRG1 $D_{\\rm perp}$ value falling below its DR2 value of $5.08\\pm0.37$ and the pivot equation-of-state $w(z=0.5)$ moving more than about 2σ away from $-1$ in a joint BAO+CMB fit, the paper's conclusion that DR2 moved toward Planck ΛCDM with no evidence for evolving dark energy would be contradicted.","supporting_citations":[],"review_version":1}