REVIEW 5 minor 66 references
Demonstration of deuterium's enhanced sensitivity to symmetry violations governed by the Standard-Model Extension
T0 review · 0 major / 5 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read Deuterium's large internal proton momentum amplifies sensitivity to CPT and Lorentz violations, and a null two-week sidereal search yields first-ever limits on spin-independent proton coefficients plus 4- and 14-order-of-magnitude…
desk verdict A careful experiment that delivers the first deuterium-based SME constraints, with headline numbers that rest on the standard one-coefficient-at-a-time convention; the paper is explicit about this, so the result holds up but the abstract oversells it slightly. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the momentum expectation value $\langle |\mathbf{p}|^k \rangle$ appearing in the SME frequency-shift formulas: in the deuteron the proton's internal momentum is roughly $0.1$ GeV/$c$, against about $1$ keV/$c$ in hydrogen, so $\langle |\mathbf{p}|^2 \rangle$ and $\langle |\mathbf{p}|^4 \rangle$ are orders of magnitude larger and amplify the frequency shift a given coefficient would produce. The experiment realizes this enhancement through Rabi-type spectroscopy of the two $\Delta M_F=0$ $\sigma$ transitions, forming the sum and difference frequencies $\nu_\pm = \nu_{\sigma_1} \pm \nu_{\sigma_2}$, and fitting first- and second-harmonic sidereal variations. Equation (6) is the conversion identity that links the fitted amplitudes $A^\pm_m$ to the Sun-centered-frame SME coefficients through those momentum moments and the known angle $\vartheta$ between the static field and Earth's rotation axis.
What would settle it
A future deuterium hyperfine measurement, for example with opposite static-field direction, Ramsey interrogation, or a deuterium maser, that resolves a first- or second-harmonic sidereal amplitude above roughly 15 to 20 Hz (about 3 sigma of the current roughly 5 Hz per-amplitude uncertainty) would falsify the paper's null result; continued nulls at sub-Hz precision would confirm it.
Extended reading notes
Core claim
The paper's central claim is that deuterium's enhanced internal proton momentum makes hyperfine spectroscopy of D a far more sensitive probe of nonrelativistic proton SME coefficients than hydrogen, and that a null sidereal search in two ground-state D transitions yields the resulting constraints. Combining the two transition frequencies into $\nu_{\sigma_1}-\nu_{\sigma_2}$ and $\nu_{\sigma_1}+\nu_{\sigma_2}$ separates spin-dependent from spin-independent contributions, and the sidereal amplitudes $A^-_1$, $A^+_1$, and $A^+_2$ are all zero within about 5 to 6 Hz. Under the one-coefficient-at-a-time assumption, these amplitudes become bounds: first-ever limits on the spin-independent coefficients $c^{\mathrm{NR}}_{p221}-a^{\mathrm{NR}}_{p221}$, $c^{\mathrm{NR}}_{p222}-a^{\mathrm{NR}}_{p222}$, $c^{\mathrm{NR}}_{p421}-a^{\mathrm{NR}}_{p421}$, and $c^{\mathrm{NR}}_{p422}-a^{\mathrm{NR}}_{p422}$, together with improvements by 4 and 14 orders of magnitude over hydrogen-maser results for spin-dependent $k=2$ and $k=4$ coefficients. Along the way, the measurement determines $\nu^D_0 = 327\,384\,354.9(28)$ Hz, the best in-beam value of the deuterium zero-field hyperfine splitting.
Load-bearing premise
The bounds are derived assuming only one kind of symmetry-violating effect is active at a time; if several effects happen to cancel, the limits would apply only to specific combinations of them, not to each effect individually.
Editorial extensions
If this is right
- Spin-independent proton SME coefficients with momentum power $k=2$ and $k=4$ are constrained for the first time, at the $10^{-19}$ to $10^{-20}$ GeV$^{-k}$ level.
- Spin-dependent $k=2$ and $k=4$ proton coefficients are now bounded 4 and 14 orders of magnitude more tightly than by hydrogen masers, closing a wide window for CPT-odd and CPT-even proton operators.
- The null sidereal amplitudes imply that any Lorentz or CPT violation in this sector must produce frequency amplitudes below about 6 Hz at this sensitivity, and the deuterium hyperfine splitting is determined to a total uncertainty of 2.8 Hz.
- The same momentum-enhancement logic can be pushed further with reversed static-field orientation, Ramsey interrogation, lower beam velocities, or a dedicated deuterium maser, all of which the paper names as routes to improved precision and resolution.
Reading between the lines
- If the one-coefficient-at-a-time assumption is relaxed, the present amplitude limits apply only to specific linear combinations of SME coefficients; individual bounds require assuming no accidental cancellations, an assumption that future experiments with different field directions could break.
- The momentum-enhancement mechanism is not limited to deuterium: nuclei with still higher internal momenta, such as tritium or helium-3, could in principle push proton or neutron SME bounds further, at the cost of larger nuclear-structure uncertainties.
- A deuterium maser using the same enhancement but with maser-level stability would likely convert the current roughly 5 Hz per-amplitude uncertainty into sub-Hz sensitivity, testing the same coefficients at higher momentum-power $k$.
- The measured zero-field splitting provides an independent in-beam anchor for $\nu^D_0$; combined with future muonic-deuterium spectroscopy, it could help separate nuclear-structure effects from new-physics shifts in the deuteron.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper reports hyperfine spectroscopy of the two ΔMF = 0 ground-state transitions in atomic deuterium using a Rabi-type beamline. The σ1 and σ2 transition frequencies are measured in interleaved resonance pairs, and the difference and sum frequencies are searched for sidereal variations. All measured amplitudes are consistent with zero. Using the SME relations of Ref. [24], the authors translate the null amplitudes into limits on nonrelativistic proton SME coefficients, claiming first constraints on the spin-independent k=2,4 coefficients and improvements over hydrogen-maser limits for the spin-dependent k=2,4 coefficients. They also extract a deuterium zero-field hyperfine splitting of 327.384 354 9(28) MHz, consistent with literature and the most precise in-beam value. The analysis uses an empirical line-shape template, offset corrections, Lomb-Scargle periodograms with p-values, and modified Birge ratio adjustments.
Significance. If the results hold, the paper provides the first constraints on the nonrelativistic proton spin-independent SME coefficients with momentum powers k=2 and 4, and it improves the spin-dependent limits by many orders of magnitude through the deuteron's internal momentum enhancement. The experimental treatment is careful: interleaved reference measurements suppress drifts, the empirical template is validated across two campaigns, the offset-correction systematics are quantified, and the Lomb-Scargle analysis includes significance estimates. The paper also reports a precise beam value of the deuterium zero-field hyperfine splitting. The authors are explicit in the body that the individual coefficient limits in Table II are obtained by allowing only one effective coefficient to be nonzero at a time, which is the standard convention in SME analyses.
minor comments (5)
- [Abstract and Conclusion] The abstract and conclusion state the coefficient constraints and the 4- and 14-order improvements without the qualifier that these are one-at-a-time limits. Because Eqs. (6) show that each measured amplitude constrains a sum over momentum powers k and spin weights q, the headline claims should be accompanied by a phrase such as 'under the usual one-at-a-time assumption' to avoid the impression that the limits are simultaneous.
- [Analysis and results, systematic investigations] The statement that using the campaign-specific template parameters 'produces the same results for the complex amplitudes within 5% of the statistical uncertainty' should be made more precise: the authors should state whether this is a 5% change of the amplitude values or of their error bars, and whether this effect is included in the 'common sys' entries of Table I.
- [End Matter §C] The final uncertainty of 2.8 Hz for ν_D0 is said to encompass systematics from the way ν_c is defined by the empirical fit, but the text only explains that the statistical uncertainty is scaled by a modified Birge ratio of 1.6. Please state explicitly how the systematic contribution is combined with the Birge-scaled statistical uncertainty to arrive at 2.8 Hz.
- [Table II and Eq. (2)] The notation 'H NR(0B) p211, -g NR(0B) p211' is potentially confusing because the measured spin-dependent amplitude is proportional to T = g - H. The caption should clarify that the quoted bound applies separately to H (with g set to zero) and to -g (with H set to zero), in accordance with the one-at-a-time convention.
- [Theory, Eq. (3)] The momentum expectation values ⟨|p|^k⟩ are taken from Tab. 1 of Ref. [24]. Including these numerical values for k=0,2,4 in the manuscript would make the claimed sensitivity enhancement quantitative and the analysis easier to check without consulting the theory paper.
Circularity Check
No significant circularity: the SME coefficient limits are obtained by linear inversion of independently measured null sidereal amplitudes through fixed external-theory relations; the one-at-a-time assumption is a stated interpretation caveat, not a circular reduction.
full rationale
The derivation chain is not circular. The measured inputs are the central hyperfine transition frequencies νcσ1 and νcσ2 obtained from empirical line-shape fits, and the sidereal amplitudes A±m are extracted by the purely data-driven fit in Eq. (5), which contains no SME coefficients. The conversion from those amplitudes to proton SME coefficients, Eq. (6), is a linear mapping whose prefactors use momentum expectation values ⟨|p|k⟩ taken from the external nuclear/SME calculation of Ref. [24] (e.g., Tab. 1), not from the data. Thus the Table II bounds are inversions of independently fitted null amplitudes through a fixed, externally supplied theory; no fitted parameter is relabeled as a prediction. The paper explicitly flags the one-at-a-time convention: "Individual constraints are obtained by allowing only one of the effective coefficients to differ from zero at a time" (Analysis and results). This is a degeneracy caveat, since Eq. (6) provides fewer measured amplitudes than unknown coefficients, so the tabulated values are conditional single-coefficient limits rather than simultaneous constraints. That affects interpretation and quoting, but it is not a circular reduction: the SME coefficients are not defined by the measured amplitudes, and the momentum factors are not fitted to the null result. No load-bearing self-citation appears here: the theory relations cited are from Vargas 2024 (Ref. [24]) and Kostelecký–Vargas (Refs. [23,37]), none of whom are authors of the present paper. The deuterium hyperfine-splitting result is likewise not circular, because Eq. (7) uses only the measured transition frequencies; the literature value is used for the scan scale but is not imposed in the fit. Overall, the paper's central claims are self-contained against its measured inputs, with the single-coefficient assumption being an explicit, non-circular limitation.
Assumptions & free parameters
free parameters (1)
- Empirical line-shape parameters (xi, Omega_R, tau_int, rho, Omega_L, Gamma) =
Tab. III: e.g., Omega_R = 10.77 krad/s, tau_int = 0.2768 ms, Gamma = 43.5 krad/s
assumptions (5)
- domain assumption The Standard-Model Extension is the correct parametrization of Lorentz/CPT violation, including nonminimal operators of arbitrary mass dimension.
- domain assumption The nonrelativistic Hamiltonian and momentum expectation values <|p|^k> from Vargas (2024), Ref [24], are correct.
- standard math The Breit-Rabi formula and 2022 CODATA constants correctly describe the Zeeman shifts and conversion factors.
- ad hoc to paper Only one effective SME coefficient is nonzero at a time when deriving individual limits.
- domain assumption Electron and neutron SME coefficients can be neglected in the interpretation.
Cite this review
Pith. "Pith review of Demonstration of deuterium's enhanced sensitivity to symmetry violations governed by the Standard-Model Extension." pith.science (2026). https://pith.science/paper/Q6EMLZ4Z
@misc{pith2026250707473,
author = {Pith},
title = {Pith review of: Demonstration of deuterium's enhanced sensitivity to symmetry violations governed by the Standard-Model Extension},
year = {2026},
howpublished = {\url{https://pith.science/paper/Q6EMLZ4Z}},
note = {Machine review of arXiv:2507.07473}
}
read the original abstract
We have performed hyperfine spectroscopy of two transitions in ground-state deuterium and searched for violations of CPT and Lorentz symmetry that would manifest as sidereal variations of the observed transition frequencies. Several nonrelativistic proton coefficients of the Standard-Model Extension framework have been addressed. The spin-independent coefficients with momentum power k=2,4 are constrained for the first time. Bounds on spin-dependent coefficients are improved by exploiting a sensitivity enhancement originating from the relative momenta of the nucleons in the deuteron. The best previous constraints by hydrogen maser measurements are surpassed by 4 and 14 orders of magnitude for coefficients with k=2 and 4, respectively.
Figures
Reference graph
Works this paper leans on
-
[24]
A. J. Vargas, Phys. Rev. D109, 055001 (2024)
work page 2024
- [1]
-
[2]
S. Rau, F. Heiße, F. K¨ ohler-Langes, S. Sasidharan, R. Haas, D. Renisch, C. E. D¨ ullmann, W. Quint, S. Sturm, and K. Blaum, Nature585, 43 (2020)
work page 2020
- [3]
-
[4]
J. E. Nafe and E. B. Nelson, Phys. Rev.73, 718 (1948)
work page 1948
-
[5]
R. Pohl, A. Antognini, F. Nez, F. D. Amaro, F. Biraben, J. M. R. Cardoso, D. S. Covita, A. Dax, S. Dhawan, L. M. P. Fernandeset al.Nature466, 213 (2010)
work page 2010
-
[6]
A. Antognini, F. Nez, K. Schuhmann, F. D. Amaro, F. Biraben, J. M. R. Cardoso, D. S. Covita, A. Dax, S. Dhawan, M. Diepoldet al.Science339, 417 (2013)
work page 2013
-
[7]
R. Pohl, F. Nez, L. M. P. Fernandes, F. D. Amaro, F. Biraben, J. M. R. Cardoso, D. S. Covita, A. Dax, S. Dhawan, M. Diepoldet al.Science353, 669 (2016)
work page 2016
Show all 66 references
-
[8]
Gao and M
H. Gao and M. Vanderhaeghen, Rev. Mod. Phys.94, 015002 (2022)
2022
-
[9]
Hernandez, A
O. Hernandez, A. Ekstr¨ om, N. Nevo Dinur, C. Ji, S. Bacca, and N. Barnea, Physics Letters B778, 377 (2018)
2018
-
[10]
Gotta, Progress in Particle and Nuclear Physics52, 133 (2004)
D. Gotta, Progress in Particle and Nuclear Physics52, 133 (2004)
2004
-
[11]
Strauch, F
T. Strauch, F. D. Amaro, D. F. Anagnostopoulos, P. B¨ uhler, D. S. Covita, H. Gorke, D. Gotta, A. Gru- ber, A. Hirtl, P. Indelicatoet al.Phys. Rev. Lett.104, 142503 (2010)
2010
-
[12]
Iwasaki, R
M. Iwasaki, R. S. Hayano, T. M. Ito, S. N. Nakamura, T. P. Terada, D. R. Gill, L. Lee, A. Olin, M. Salomon, S. Yenet al.Phys. Rev. Lett.78, 3067 (1997)
1997
-
[13]
G. Beer, A. M. Bragadireanu, M. Cargnelli, C. Curceanu- Petrascu, J.-P. Egger, H. Fuhrmann, C. Guaraldo, M. Ili- escu, T. Ishiwatari, K. Itahashiet al.Phys. Rev. Lett.94, 212302 (2005)
2005
-
[14]
Curceanu, C
C. Curceanu, C. Guaraldo, M. Iliescu, M. Cargnelli, R. Hayano, J. Marton, J. Zmeskal, T. Ishiwatari, M. Iwasaki, S. Okada, D. L. Sirghi, and H. Tatsuno, Rev. Mod. Phys.91, 025006 (2019)
2019
-
[15]
Richard and M
J. Richard and M. Sainio, Physics Letters B110, 349 (1982)
1982
-
[16]
Wycech, A
S. Wycech, A. Green, and J. Niskanen, Physics Letters B152, 308 (1985)
1985
-
[17]
Baker, C
C. Baker, C. Batty, S. Clark, J. Moir, S. Sakamoto, J. Davies, J. Lowe, J. Nelson, G. Pyle, A. Selvarajah et al.Nuclear Physics A483, 631 (1988)
1988
-
[18]
Augsburger, D
M. Augsburger, D. Anagnostopoulos, G. Borchert, D. Chatellard, J.-P. Egger, P. El-Khoury, H. Gorke, D. Gotta, P. Hauser, P. Indelicatoet al.Physics Letters B461, 417 (1999)
1999
-
[19]
Augsburger, D
M. Augsburger, D. Anagnostopoulos, G. Borchert, D. Chatellard, J.-P. Egger, P. El-Khoury, H. Gorke, D. Gotta, P. Hauser, P. Indelicatoet al.Nuclear Physics A658, 149 (1999). 7
1999
-
[20]
D. F. Phillips, M. A. Humphrey, E. M. Mattison, R. E. Stoner, R. F. C. Vessot, and R. L. Walsworth, Phys. Rev. D63, 111101 (2001)
2001
-
[21]
M. A. Humphrey, D. F. Phillips, E. M. Mattison, R. F. C. Vessot, R. E. Stoner, and R. L. Walsworth, Phys. Rev. A68, 063807 (2003)
2003
-
[22]
R. M. Potvliege, A. Nicolson, M. P. A. Jones, and M. Spannowsky, Phys. Rev. A108, 052825 (2023)
2023
-
[23]
V. A. Kosteleck´ y and A. J. Vargas, Phys. Rev. D92, 056002 (2015)
2015
-
[25]
I. I. Rabi, J. R. Zacharias, S. Millman, and P. Kusch, Phys. Rev.53, 318 (1938)
1938
-
[26]
Colladay and V
D. Colladay and V. A. Kosteleck´ y, Phys. Rev. D55, 6760 (1997)
1997
-
[27]
Colladay and V
D. Colladay and V. A. Kosteleck´ y, Phys. Rev. D58, 116002 (1998)
1998
-
[28]
Bluhm, V
R. Bluhm, V. A. Kosteleck´ y, and N. Russell, Phys. Rev. Lett.82, 2254 (1999)
1999
-
[29]
Breit and I
G. Breit and I. I. Rabi, Phys. Rev.38, 2082 (1931)
1931
-
[30]
D. J. Wineland and N. F. Ramsey, Phys. Rev. A5, 821 (1972)
1972
-
[31]
P. J. Mohr, D. B. Newell, B. N. Taylor, and E. Tiesinga, Rev. Mod. Phys.97, 025002 (2025)
2025
-
[32]
V. A. Kosteleck´ y and N. Russell, Rev. Mod. Phys.83, 11 (2011)
2011
-
[33]
V. A. Kosteleck´ y and N. Russell, arXivv17(2024), https://doi.org/10.48550/arXiv.0801.0287
2024 doi
-
[34]
V. A. Kosteleck´ y and M. Mewes, Phys. Rev. D80, 015020 (2009)
2009
-
[35]
V. A. Kosteleck´ y and M. Mewes, Phys. Rev. D88, 096006 (2013)
2013
-
[36]
V. A. Kosteleck´ y and Z. Li, Phys. Rev. D99, 056016 (2019)
2019
-
[37]
V. A. Kosteleck´ y and A. J. Vargas, Phys. Rev. D98, 036003 (2018)
2018
-
[38]
Widmann, R
E. Widmann, R. Hayano, M. Hori, and T. Ya- mazaki, Nuclear Instruments and Methods in Physics Re- search Section B: Beam Interactions with Materials and Atoms214, 31 (2004), low Energy Antiproton Physics (LEAP’03)
2004
-
[39]
Diermaier, C
M. Diermaier, C. Jepsen, B. Kolbinger, C. Malbrunot, O. Massiczek, C. Sauerzopf, M. Simon, J. Zmeskal, and E. Widmann, Nature communications8, 1 (2017)
2017
-
[40]
Malbrunot, M
C. Malbrunot, M. Diermaier, M. Simon, C. Amsler, S. Arguedas Cuendis, H. Breuker, C. Evans, M. Fleck, B. Kolbinger, A. Lanzet al.Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 935, 110 (2019)
2019
-
[41]
Nowak, C
L. Nowak, C. Malbrunot, M. Simon, C. Amsler, S. Arguedas Cuendis, S. Lahs, A. Lanz, A. Nanda, M. Wiesinger, T. Wolz, and E. Widmann, Physics Let- ters B858, 139012 (2024)
2024
-
[42]
M. W. Reynolds, M. E. Hayden, and W. N. Hardy, Jour- nal of Low Temperature Physics84, 87 (1991)
1991
-
[43]
¨Oz¸ sahin, T
G. ¨Oz¸ sahin, T. S ¸im¸ sek, M.¨Unl¨ u, O. Kiri¸ s, S. K¨ ose, H. Musta¸ co˘ glu, F.¨Ozt¨ urk, and V. Akan, in2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting(2017) pp. 101–102
2017
-
[44]
Debus and P
C. Debus and P. H. Bolivar, Applied Physics Letters 91, 184102 (2007), https://pubs.aip.org/aip/apl/article- pdf/doi/10.1063/1.2805016/14385579/184102 1 online.pdf
2007 doi
-
[45]
Guillou-Camargo, V
F. Guillou-Camargo, V. M´ enoret, E. Cantin, O. Lopez, N. Quintin, E. Camisard, V. Salmon, J.-M. L. Merdy, G. Santarelli, A. Amy-Kleinet al.Appl. Opt.57, 7203 (2018)
2018
-
[46]
Cantin, M
E. Cantin, M. Tønnes, R. L. Targat, A. Amy-Klein, O. Lopez, and P.-E. Pottie, New Journal of Physics23, 053027 (2021)
2021
-
[47]
https://www.refimeve.fr/index.php/en/
-
[48]
The theoretical prospects of the experiment discussed in [24] useϑ∼49 ◦ as those are based on a magnetic field pointing in the opposite direction than applied in this work
-
[49]
J. T. VanderPlas, The Astrophysical Journal Supplement Series236, 16 (2018)
2018
-
[50]
J. T. VanderPlas and ˇZeljko Ivezic´, The Astrophysical Journal812, 18 (2015)
2015
-
[51]
Vanderplas, A
J. Vanderplas, A. J. Connolly, ˇZeljko Ivezi´ c, and A. G. Gray, 2012 Conference on Intelligent Data Understanding 47 (2012)
2012
-
[52]
N. R. Lomb, Astrophysics and Space Science39, 447 (1976)
1976
-
[53]
J. D. Scargle, Astrophys. J.263, 835 (1982)
1982
-
[54]
Astropy Collaboration, A. M. Price-Whelanet al.The Astrophysical Journal935, 167 (2022)
2022
-
[55]
Astropy Collaboration, A. M. Price-Whelanet al.The Astronomical Journal156, 123 (2018)
2018
-
[56]
Astropy Collaboration, T. P. Robitailleet al.Astronomy & Astrophysics558, A33 (2013),
2013
-
[57]
L. S. Dreissen, C.-H. Yeh, H. A. F¨ urst, K. C. Grense- mann, and T. E. Mehlst¨ aubler, Nature Communications 13, 7314 (2022)
2022
-
[58]
R. V. Baluev, Monthly Notices of the Royal Astronomical Society385, 1279 (2008),
2008
-
[59]
Bodnar and C
O. Bodnar and C. Elster, Metrologia51, 516 (2014)
2014
-
[60]
Kusch, Phys
P. Kusch, Phys. Rev.100, 1188 (1955)
1955
-
[61]
Killian, Z
C. Killian, Z. Burkley, P. Blumer, P. Crivelli, F. P. Gustafsson, O. Hanski, A. Nanda, F. Nez, V. Nesvizhevsky, S. Reynaudet al.The European Phys- ical Journal D77, 50 (2023)
2023
-
[62]
Killian, P
C. Killian, P. Blumer, P. Crivelli, O. Hanski, D. Kloppen- burg, F. Nez, V. Nesvizhevsky, S. Reynaud, K. Schreiner, M. C. Simonet al.The European Physical Journal D78, 132 (2024)
2024
-
[63]
N. F. Ramsey, Phys. Rev.78, 695 (1950)
1950
-
[64]
N. F. Ramsey, Reviews of modern physics62, 541 (1990)
1990
-
[65]
Progress towards ramsey hyperfine spec- troscopy in asacusa,
A. Nanda, “Progress towards ramsey hyperfine spec- troscopy in asacusa,” inCPT and Lorentz Symmetry (worldscientific, 2020) pp. 201–203
2020
-
[66]
COMSOL Multiphysics ®, https://www.comsol.com . 8 End Matter §A Data acquisition protocol—The sequence of measurements performed to acquire a resonance pair (succinctly described in the main text) is as follows: ref-σn1(1) 1 -ref-σn2(1) 2 -ref-...-ref-σn1(25) 1 -ref-σn2(25) 2 ...
Reviewed August 6, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.