Response to: "Isotropic deceleration and near-zero baseline acceleration in Pantheon+ supernovae: new arguments in the dark energy debate''

Animesh Sah; Mohamed Rameez; Subir Sarkar

Response to: "Isotropic deceleration and near-zero baseline acceleration in Pantheon+ supernovae: new arguments in the dark energy debate''

T0 review · 0 major / 3 minor · reviewed 2026-08-04 · deepseek-v4-flash

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Pith's one-line read Misread sky coordinates invalidate a supernova dark-energy counterclaim

desk verdict R26 made a coordinate-system error that is nailed down by an exact reproduction of their 724/840 split; the corrected split is 539/1025. read the letter →

arxiv 2608.02484 v1 pith:VRQE56M6 submitted 2026-08-03 astro-ph.CO gr-qc

Animesh Sah , Mohamed Rameez , Subir Sarkar This is my paper

classification astro-ph.COgr-qc

keywords darkenergytypeIasupernovaePantheon+CMBdipolehemispheretestcoordinatetransformationdecelerationparametercosmicanisotropy

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This short response rebuts a recent claim that the deceleration parameter measured from Type Ia supernovae is equally positive in the CMB dipole and anti-dipole hemispheres, which would contradict earlier evidence for a dipole anisotropy. Reproducing the disputed hemisphere split from the same supernova sample shows that the result only appears when the CMB dipole's Galactic coordinates (264°, 48°) are used as if they were equatorial. When the direction is properly transformed to ICRS, (167.8°, -7.1°), the sample splits into 539 versus 1025 rather than the reported 724 versus 840. The paper concludes that the contested test was not centered on the CMB dipole and therefore says nothing against the anisotropy claim. If correct, this removes a central counter-argument in the dark energy debate.

What carries the argument

The load-bearing object is the coordinate transformation of the CMB dipole direction from Galactic to ICRS equatorial coordinates, together with the spherical dot product cosθ = sinδ sinδ0 + cosδ cosδ0 cos(α-α0). The paper applies this formula twice: once with (α0,δ0) = (264°,48°) (the un-transformed Galactic values) and once with the correct ICRS values (167.8°,-7.1°), and compares the resulting hemisphere counts to the published numbers.

What would settle it

Recalculate the hemispheric q_m values using the correct direction (167.8°, -7.1°): if the values differ substantially from +1.45 and +1.55, the coordinate error is indeed the cause; if the same values reappear, the conclusion would be challenged. Alternatively, verify from the Pantheon+ documentation whether positions are stored in ICRS; if they were stored in Galactic coordinates, the paper's premise would collapse.

Watch

Extended reading notes

Core claim

The paper's central discovery is a replication: taking the numbers (264°, 48°) from the criticized analysis and treating them as equatorial right ascension and declination exactly reproduces the reported hemisphere split of 724/840 supernovae in the N=1564 Pantheon+ sample, whereas the CMB dipole direction properly converted from Galactic to ICRS coordinates, (167.8°, -7.1°), yields 539/1025. This shows the criticized analysis computed cosθ with a reference direction that was not the CMB dipole at all, because the supernova positions in Pantheon+ are given in equatorial coordinates, so the reference direction must also be equatorial.

Load-bearing premise

The conclusion rests on the premises that Pantheon+ sky positions are ICRS equatorial and that the CMB dipole direction in ICRS is (167.8°, -7.1°); if either premise is wrong, the corrected 539/1025 split does not follow.

Editorial extensions

If this is right

The reported q_m values of +1.45 and +1.55 for the dipole and anti-dipole hemispheres do not constrain any anisotropy aligned with the CMB dipole.
The earlier dipole-anisotropy claim, based on the same Pantheon+ catalogue, is not contradicted by this particular analysis.
Any future hemisphere test on Pantheon+ data must convert all sky positions and reference directions to a single coordinate frame before computing cosθ.
The corrected split differs substantially from the published counts, showing that the coordinate error fully accounts for the reported numbers.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

A testable extension: refit the deceleration parameter q_m for hemispheres defined by the correct CMB dipole direction (167.8°, -7.1°) to see whether the dipole/anti-dipole asymmetry persists; the current paper only corrects the split, not the q_m values.
The same coordinate-convention pitfall may affect other analyses that mix Galactic and equatorial catalogues, so a systematic check of coordinate frames across the cosmology literature could reveal additional spurious signals.
If the Pantheon+ data release were to document its coordinate frame more prominently, future replications would be less error-prone; the paper implicitly makes that case.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

This short rebuttal is convincing. Ray et al. stated their reference direction as the CMB dipole in Galactic coordinates, (l,b) = (264°,48°), then went on to evaluate the dot product with supernova positions in equatorial coordinates without transforming. Sah et al. show that using (264°,48°) as (α,δ) gives exactly the 724/840 count reported in R26's Fig. 3, while the correctly transformed ICRS direction (167.8°,−7.1°) gives 539/1025. That exact numerical fingerprint is the whole ballgame — you cannot ask for a cleaner diagnosis of a mislabeling error. The additional ΔLLH≈0.2 check is a nice touch, even if not decisive on its own.

The paper is narrow, but it does what a rebuttal should do: it isolates the slip, exposes it with reproducible counting, and draws the only logical conclusion — that R26's hemisphere test was not centered on the CMB dipole, so their claim about isotropic deceleration in the dipole/anti-dipole hemispheres does not constrain the SRS26 anisotropy. The authors do not recompute q_m in the correctly aligned hemispheres, but they don't need to; showing that the test was miscentered is sufficient to invalidate that particular counterargument.

The soft spots are minor. The assumption that Pantheon+SH0ES positions are ICRS equatorial is standard and verifiable from the data release, but it is asserted rather than cited. The paper also does not release its selection and counting code, so independent verification requires a bit of effort — though the exact match with R26's published number already rules out most alternatives. The tone is sharp: saying the R26 conclusion is "baseless" is strong, but in this case the evidence supports it.

This is a useful correction in an active debate, not a new discovery. Anyone working on bulk flows, the Hubble tension, or the SRS26 claim should read it. I'd send it to peer review without hesitation; a referee can check the spherical trig in ten minutes. The paper is honest, technically sound, and addresses a real error in a published claim. I would cite it if I were writing about this debate.

Referee Report

0 major / 3 minor

Summary. Ray et al. (R26) claimed that the deceleration parameter q_m derived from Pantheon+ SNe is nearly equal in the CMB dipole and anti-dipole hemispheres, contradicting the authors' prior detection of a dipole-aligned anisotropy. This response argues that R26 made a coordinate-system error: they quoted the CMB dipole direction as (ℓ,b)=(264°,48°) but then evaluated the hemisphere split using these numbers as equatorial (α,δ), miscentering the hemispheres. The authors reproduce R26's reported 724/840 split only when (264°,48°) is treated as equatorial, and show that the correct ICRS CMB dipole (167.8°,−7.1°) yields 539/1025. They conclude that R26's test was not actually centred on the CMB dipole, invalidating their check of SRS26.

Significance. This is a concise, decisive bookkeeping correction. The exact reproduction of R26's hemisphere counts provides a strong numerical fingerprint that the original calculation treated Galactic coordinates as equatorial. The coordinate conventions involved (Pantheon+ positions in ICRS, CMB dipole direction ~(168°,−7°) in ICRS) are standard and externally checkable. If accepted, the paper removes a specific empirical counter-argument to the SRS26 dipole claims. The response is appropriately scoped: it does not re-derive q_m maps or discuss broader dark-energy evidence, but that is not required for the narrow claim. The main weakness is the absence of a citation for the ICRS dipole coordinate and the lack of full sample-selection details, both of which are minor.

minor comments (3)

[Main text, §1] The load-bearing value (167.8°,−7.1°) is asserted without reference. Please cite the standard measurement of the CMB dipole (e.g., Planck Collaboration) and/or show the Galactic-to-ICRS transformation so the reader can verify the conversion.
[Main text, §1] The sentence 'We reproduce the sample selection of R26 (N=1564)' does not specify the exact cuts used. Since the reproduction of the 724/840 split is the central evidence, please describe the selection (e.g., redshift limits and any quality cuts) or provide a link to code/data.
[Table I] The column header 'Reference direction [ICRS]' is confusing for the first row, since (264°,48°) is not an ICRS direction; it is the raw Galactic numbers used as equatorial coordinates. Please relabel to something like 'Reference direction used in Eq. (1)'.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the coordinate-mismatch claim rests on an externally checkable bookkeeping calculation, not on fitted inputs or self-citations.

full rationale

The paper's central claim is that Ray et al. (R26) used the Galactic coordinates (ℓ,b)=(264°,48°) of the CMB dipole as if they were equatorial (α,δ), so their hemisphere split was not actually centred on the CMB dipole. The evidence is an exact count reproduction: evaluating cosθ with (264°,48°) as (α0,δ0) against the Pantheon+ positions yields the N=724/840 split reported in R26's Fig. 3, while using the correctly transformed ICRS direction (167.8°,−7.1°) gives 539/1025. This is arithmetic applied to published catalogue data and a standard coordinate transformation; it does not depend on the authors' own prior analysis [2] for its validity. The self-citations ([2], [3]) appear only as context or background physical expectation and are not load-bearing for the coordinate-error argument. No fitted parameter is relabelled as a prediction, no uniqueness theorem from the authors' prior work is invoked, and no ansatz is smuggled in via citation. The only unstated premise is that Pantheon+SH0ES tabulates ICRS equatorial coordinates and that the Galactic-to-ICRS transformation is standard; both are textbook and externally verifiable, and the exact match with R26's reported split corroborates the premise. Thus there is no circular step in the derivation chain.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

No free parameters are fitted in this reply; the dipole direction is fixed by the external CMB dipole measurement, and the reported ΔLLH≈0.2 is a test statistic, not a fitted value. The calculation relies on three background premises: the standard spherical-trig separation formula, the Galactic→ICRS conversion of the CMB dipole (asserted without citation but matching standard values), and the claim that Pantheon+ positions are ICRS. No new entities are postulated.

assumptions (3)

standard math Eq. (1): cosθ = sinδ sinδ0 + cosδ cosδ0 cos(α−α0) gives the angular separation between a supernova and a reference direction.
Standard spherical-trigonometry formula, used to partition the sample into hemispheres.
domain assumption The CMB dipole direction in Galactic coordinates (ℓ,b)=(264°,48°) transforms to ICRS (α,δ)=(167.8°,−7.1°).
Standard, externally verified transformation; it is load-bearing for the corrected split but is asserted in the text without citation.
domain assumption Pantheon+SH0ES tabulates supernova positions in ICRS Equatorial coordinates (RA/Dec).
Quoted claim about the data release [6]; required for the conclusion that R26 should have transformed before applying Eq. (1).

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Cite this review

Pith. "Pith review of Response to: "Isotropic deceleration and near-zero baseline acceleration in Pantheon+ supernovae: new arguments in the dark energy debate''." pith.science (2026). https://pith.science/paper/VRQE56M6

@misc{pith2026260802484,
  author       = {Pith},
  title        = {Pith review of: Response to: "Isotropic deceleration and near-zero baseline acceleration in Pantheon+ supernovae: new arguments in the dark energy debate''},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/VRQE56M6}},
  note         = {Machine review of arXiv:2608.02484}
}

abstract

Ray et al. [1] have claimed that the acceleration of the Hubble expansion rate inferred from Type Ia supernovae in the Pantheon+ catalogue "is equally strong in the CMB dipole ($q_m = + 1.45$) and anti-dipole hemispheres ($+ 1.55$), directly contradicting the SRS26 anisotropy argument". Here SRS26 refers to our analysis [2] which showed that "locally $q_0$ has a strong dipole anisotropy aligned approximately with the bulk flow, and only a small monopole component remains at distances exceeding a few hundred Mpc". We find that these authors confused Equatorial with Galactic coordinates, thereby getting the CMB dipole direction wrong. Hence their conclusion is baseless.

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Reference graph

Works this paper leans on

8 extracted references · 5 linked inside Pith

[1]

the values (264◦, 48◦) used as equatorial coordinates, withouttransforming from Galactic to ICRS, and
[2]

The first row of Table I reproduces the N = 724/840 split reported in the caption of Fig

the correctly transformed CMB dipole direction: (167.8◦,−7.1 ◦) in equatorial coordinates. The first row of Table I reproduces the N = 724/840 split reported in the caption of Fig. 3 of R26. This shows that R26 erred in evaluating Eq.( 1) taking the numerical values (264 ◦, 48◦) to be ( α0, δ0), i.e.without applying the Galactic-to-ICRS transformation req...
[3]

S. Ray, M. Khlopov, A. Sanyal, R. Sengupta and M. Kras- nov, [arXiv:2607.20570 [astro-ph.CO]]

arXiv
[4]

A. Sah, M. Rameez and S. Sarkar, Mon. Not. Roy. Astron. Soc.549(2026) stag844 [arXiv:2606.09650 [astro-ph.CO]]

arXiv 2026
[5]

A. Sah, M. Rameez, S. Sarkar and C. G. Tsagas, Eur. Phys. J. C85(2025) 596 [arXiv:2411.10838 [astro-ph.CO]]

arXiv 2025
[6]

Chung, Y

C. Chung, Y. W. Lee, J. Son, S. Park and H. Cho, Mon. Not. Roy. Astron. Soc.544(2025) 975 [arXiv:2510.13121 [astro-ph.CO]]

arXiv 2025
[7]

Chung, D

C. Chung, D. Lim, H. Cho, J. Son, S. Park, S. J. Yoon and Y. W. Lee, [arXiv:2605.21586 [astro-ph.CO]]

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[8]

Scolnic, D

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arXiv 2022

Pith tools

Reviewed August 4, 2026 · model on record in the stance chip above.

[1] [1]

the values (264◦, 48◦) used as equatorial coordinates, withouttransforming from Galactic to ICRS, and

[2] [2]

The first row of Table I reproduces the N = 724/840 split reported in the caption of Fig

the correctly transformed CMB dipole direction: (167.8◦,−7.1 ◦) in equatorial coordinates. The first row of Table I reproduces the N = 724/840 split reported in the caption of Fig. 3 of R26. This shows that R26 erred in evaluating Eq.( 1) taking the numerical values (264 ◦, 48◦) to be ( α0, δ0), i.e.without applying the Galactic-to-ICRS transformation req...

[3] [3]

S. Ray, M. Khlopov, A. Sanyal, R. Sengupta and M. Kras- nov, [arXiv:2607.20570 [astro-ph.CO]]

arXiv

[4] [4]

A. Sah, M. Rameez and S. Sarkar, Mon. Not. Roy. Astron. Soc.549(2026) stag844 [arXiv:2606.09650 [astro-ph.CO]]

arXiv 2026

[5] [5]

A. Sah, M. Rameez, S. Sarkar and C. G. Tsagas, Eur. Phys. J. C85(2025) 596 [arXiv:2411.10838 [astro-ph.CO]]

arXiv 2025

[6] [6]

Chung, Y

C. Chung, Y. W. Lee, J. Son, S. Park and H. Cho, Mon. Not. Roy. Astron. Soc.544(2025) 975 [arXiv:2510.13121 [astro-ph.CO]]

arXiv 2025

[7] [7]

Chung, D

C. Chung, D. Lim, H. Cho, J. Son, S. Park, S. J. Yoon and Y. W. Lee, [arXiv:2605.21586 [astro-ph.CO]]

arXiv

[8] [8]

Scolnic, D

D. Scolnic, D. Brout, A. Carr, A. G. Riess, T. M. Davis, A. Dwomoh, D. O. Jones, N. Ali, P. Charvu and R. Chen,et al.Astrophys. J.938(2022) 113 [arXiv:2112.03863 [astro- ph.CO]]. arXiv:2608.02484v1 [astro-ph.CO] 3 Aug 2026

arXiv 2022