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arxiv: 2605.03093 · v1 · submitted 2026-05-04 · ✦ hep-ph

Einstein-de Haas effect and induced rotation in QCD matter

Dushmanta Sahu This is my paper

Pith reviewed 2026-05-08 17:30 UTC · model grok-4.3

classification ✦ hep-ph
keywords Einstein-de Haas effectQCD matterheavy-ion collisionsmagnetic fieldsvorticityspin alignmentangular momentum
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0 comments X

The pith

Remnant magnetic fields at freeze-out induce rotations in QCD matter comparable to fluid vorticity via the Einstein-de Haas effect.

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

This paper reports the first identification of the Einstein-de Haas effect in QCD matter. The effect arises when magnetic-field-induced spin alignment in an equilibrium hadron gas generates a compensating collective rotation to conserve total angular momentum. Calculations demonstrate that even remnant magnetic fields produce induced rotations similar in magnitude to typical fluid vorticity estimates from hyperon polarization in heavy-ion collisions. This occurs without any initial vorticity input, establishing hot QCD matter as a self-vortical magnetofluid where spin-rotation coupling plays a key role in angular momentum dynamics.

Core claim

The central claim is that the Einstein-de Haas effect can be realized in an equilibrium hadron gas under external magnetic fields, leading to induced rotations ω_EdH that match typical values of fluid vorticity in relativistic nuclear collisions, all emerging purely from the magnetic field and spin alignment.

What carries the argument

The Einstein-de Haas effect, defined as the magnetomechanical coupling in which spin alignment under a magnetic field produces a compensating collective rotation to conserve total angular momentum.

If this is right

  • Collective rotation can be generated in QCD matter purely from magnetic spin alignment without initial fluid vorticity.
  • Spin-rotation coupling becomes an important, previously overlooked component of angular momentum dynamics in heavy-ion collisions.
  • Hot QCD matter behaves as a self-vortical magnetofluid due to this effect.
  • The induced rotations are comparable to those inferred from final-state hyperon polarization.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This mechanism could provide an alternative or additional source for observed hyperon polarizations in heavy-ion data.
  • Models of angular momentum in collisions may need to account for magnetic field contributions to rotation separately from hydrodynamic vorticity.
  • Further studies could explore how this effect influences other spin observables or the evolution of magnetic fields in the plasma.

Load-bearing premise

The system can be treated as an equilibrium hadron gas under an external magnetic field where spin alignment directly produces a compensating collective rotation while conserving total angular momentum.

What would settle it

A calculation or measurement demonstrating that the induced rotation from remnant magnetic fields is much smaller than the vorticity values inferred from hyperon polarization would falsify the comparability.

Figures

Figures reproduced from arXiv: 2605.03093 by Dushmanta Sahu.

Figure 1
Figure 1. Figure 1: FIG. 1: A schematic representation of how magnetic field creates a spin alignment, which in turn creates a rotation to conserve view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: Induced rotation (shown as absolute value) as a func view at source ↗
read the original abstract

In this study, we report the first identification of the Einstein-de Haas (EdH) effect in the QCD matter. The EdH effect is a fundamental magnetomechanical coupling wherein magnetic-field-induced spin alignment generates a compensating collective rotation to conserve the total angular momentum. Using an equilibrium hadron gas under an external magnetic field, we show that even remnant magnetic fields at the freeze-out produce induced rotations ($\omega_{\mathrm{EdH}}$) comparable to typical estimates of fluid vorticity in heavy-ion collisions as inferred from final-state hyperon polarization. This rotation emerges from the magnetic field alone, without any initial vorticity as input. The Einstein-de Haas effect thus establishes hot QCD matter as a self-vortical magnetofluid, where collective rotation can be generated purely from spin alignment, and identifies spin-rotation coupling as a potentially important, previously overlooked component of angular momentum dynamics in relativistic nuclear collisions.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript claims to report the first identification of the Einstein-de Haas effect in QCD matter. Using an equilibrium hadron gas model under an external magnetic field, it shows that even remnant magnetic fields at freeze-out produce induced rotations (ω_EdH) comparable to typical estimates of fluid vorticity in heavy-ion collisions as inferred from final-state hyperon polarization. This rotation is generated from the magnetic field alone, without any initial vorticity input, establishing hot QCD matter as a self-vortical magnetofluid where spin-rotation coupling is an important component of angular momentum dynamics.

Significance. If the central result holds, the work identifies a magnetomechanical coupling that could contribute to collective rotation in relativistic nuclear collisions purely via spin alignment, potentially affecting the interpretation of polarization observables and angular momentum balance in the presence of strong magnetic fields. The equilibrium model yields a concrete, parameter-free prediction for the induced ω_EdH that can be compared directly to existing vorticity estimates.

major comments (1)
  1. [Abstract and model description] Abstract and model description: the claim that remnant B fields at freeze-out induce ω_EdH comparable to fluid vorticity without initial vorticity input rests on treating the hadron gas as globally equilibrated in a static, uniform external magnetic field, so that the Boltzmann factor produces a net <S_z> per species whose total angular momentum is exactly compensated by a macroscopic rigid-body rotation Iω_EdH. In heavy-ion collisions, freeze-out occurs in a rapidly expanding, inhomogeneous, time-dependent remnant field with particles decoupling and free-streaming; no section demonstrates how local spin alignment generates the required global orbital velocity field without additional interactions or initial conditions.
minor comments (2)
  1. [Abstract] The abstract would be strengthened by including at least one key equation (e.g., the expression for ω_EdH or the sum over species for total spin angular momentum) and a numerical value or ratio showing the claimed comparability to vorticity.
  2. Notation for ω_EdH and the moment of inertia should be defined explicitly on first use to improve readability for readers outside the immediate subfield.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading and constructive feedback on our manuscript. We address the major comment below.

read point-by-point responses

  1. Referee: [Abstract and model description] Abstract and model description: the claim that remnant B fields at freeze-out induce ω_EdH comparable to fluid vorticity without initial vorticity input rests on treating the hadron gas as globally equilibrated in a static, uniform external magnetic field, so that the Boltzmann factor produces a net <S_z> per species whose total angular momentum is exactly compensated by a macroscopic rigid-body rotation Iω_EdH. In heavy-ion collisions, freeze-out occurs in a rapidly expanding, inhomogeneous, time-dependent remnant field with particles decoupling and free-streaming; no section demonstrates how local spin alignment generates the required global orbital velocity field without additional interactions or initial conditions.

    Authors: We agree that the calculation employs an equilibrium hadron gas in a static, uniform magnetic field. This framework permits a direct evaluation of the field-induced net spin per species through the Boltzmann factor and the compensating rigid-body rotation Iω_EdH required by angular-momentum conservation. The resulting parameter-free estimate shows that remnant fields at freeze-out can produce ω_EdH values comparable to typical fluid vorticity. The model is intended as an order-of-magnitude illustration of the Einstein-de Haas effect under freeze-out conditions rather than a full dynamical simulation of the expanding medium. A complete demonstration of how local spin alignments source a global velocity field would indeed require a non-equilibrium treatment (e.g., spin hydrodynamics or kinetic theory with spin-rotation coupling), which lies outside the present scope. We will revise the abstract and model-description sections to state the equilibrium assumptions and limitations more explicitly and will add a short discussion paragraph outlining how the effect could be incorporated into future dynamical models. revision: partial

Circularity Check

0 steps flagged

No significant circularity; EdH rotation follows directly from AM conservation applied to computed spin alignment.

full rationale

The paper applies the standard Einstein-de Haas mechanism: an external B field induces spin polarization via the Boltzmann factor in an equilibrium hadron gas, after which total angular momentum conservation determines the compensating rigid-body rotation ω_EdH = (total spin AM)/I. This is the definition of the EdH effect itself rather than a derived prediction that reduces to an input by construction. No self-citations, fitted parameters, or uniqueness theorems are invoked in the provided text to force the result. The setup explicitly starts from B with zero initial vorticity, and the output ω is computed rather than assumed. The derivation chain is self-contained against external benchmarks of magnetomechanical coupling.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the assumption that an equilibrium hadron gas under a remnant magnetic field exhibits the classical Einstein-de Haas mechanism, with spin alignment directly inducing collective rotation to conserve angular momentum. No free parameters or new entities are explicitly introduced in the abstract.

axioms (2)
  • domain assumption The late-stage QCD matter can be modeled as an equilibrium hadron gas in an external magnetic field.
    Invoked to calculate spin alignment and induced rotation at freeze-out.
  • domain assumption Magnetic-field-induced spin alignment produces a compensating collective rotation that conserves total angular momentum.
    This is the core Einstein-de Haas mechanism applied to the QCD system.

pith-pipeline@v0.9.0 · 5439 in / 1508 out tokens · 32132 ms · 2026-05-08T17:30:06.665185+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

35 extracted references · 35 canonical work pages

  1. [1]

    Adamczyket al.[STAR], Nature548, 62-65 (2017)

    L. Adamczyket al.[STAR], Nature548, 62-65 (2017)

    work page 2017

  2. [2]

    Skokov, A

    V. Skokov, A. Y. Illarionov and V. Toneev, Int. J. Mod. Phys. A24, 5925-5932 (2009)

    work page 2009

  3. [3]

    Yan and X

    L. Yan and X. G. Huang, Phys. Rev. D107, no.9, 094028 (2023)

    work page 2023

  4. [4]

    G. S. Pradhan, D. Sahu, S. Deb and R. Sahoo, J. Phys. G50, no.5, 055104 (2023)

    work page 2023

  5. [5]

    Sahoo, K

    B. Sahoo, K. K. Pradhan, D. Sahu and R. Sahoo, Phys. Rev. D108, no.7, 074028 (2023)

    work page 2023

  6. [6]

    Goswami, D

    K. Goswami, D. Sahu, J. Dey, R. Sahoo and R. Stock, Phys. Rev. D109, no.7, 074012 (2024)

    work page 2024

  7. [7]

    K. K. Pradhan, B. Sahoo, D. Sahu and R. Sahoo, Eur. Phys. J. C84, no.9, 936 (2024)

    work page 2024

  8. [8]

    D. E. Kharzeev and D. T. Son, Phys. Rev. Lett.106, 062301 (2011)

    work page 2011

  9. [9]

    D. E. Kharzeev, J. Liao, S. A. Voloshin and G. Wang, Prog. Part. Nucl. Phys.88, 1-28 (2016)

    work page 2016

  10. [10]

    Sahu, Phys

    D. Sahu, Phys. Lett. B872, 140081 (2026)

    work page 2026

  11. [11]

    Experimenteller Nachweis der Amp` ereschen Molekularstr¨ ome,

    A. Einstein and W. J. de Haas, “Experimenteller Nachweis der Amp` ereschen Molekularstr¨ ome,” Verhandlungen der Deutschen Physikalischen Gesellschaft, vol. 17, pp. 152–170, 1915

    work page 1915

  12. [12]

    Ganzhorn, M., Klyatskaya, S., Ruben, M. et al. Quan- tum Einstein-de Haas effect. Nature Communications 7, 11443 (2016)

    work page 2016

  13. [13]

    Matsui, H. et al. ,Observation of the Einstein–de Haas effect in a Bose–Einstein condensate. Science 391, 384- 388(2026)

    work page 2026

  14. [14]

    Florkowski, A

    W. Florkowski, A. Kumar and R. Ryblewski, Prog. Part. Nucl. Phys.108, 103709 (2019)

    work page 2019

  15. [15]

    Singh, M

    R. Singh, M. Shokri and S. M. A. T. Mehr, Nucl. Phys. A1035, 122656 (2023)

    work page 2023

  16. [16]

    J. H. Gao, Z. T. Liang, S. Pu, Q. Wang and X. N. Wang, Phys. Rev. Lett.109, 232301 (2012)

    work page 2012

  17. [17]

    Weickgenannt, X

    N. Weickgenannt, X. L. Sheng, E. Speranza, Q. Wang and D. H. Rischke, Phys. Rev. D100, no.5, 056018 (2019)

    work page 2019

  18. [18]

    Karpenko and F

    I. Karpenko and F. Becattini, Eur. Phys. J. C77, no.4, 213 (2017)

    work page 2017

  19. [19]

    Adamet al.[STAR], Phys

    J. Adamet al.[STAR], Phys. Rev. Lett.123, no.13, 132301 (2019)

    work page 2019

  20. [20]

    Fukushima, D

    K. Fukushima, D. E. Kharzeev and H. J. Warringa, Phys. Rev. D78, 074033 (2008)

    work page 2008

  21. [21]

    D. T. Son and N. Yamamoto, Phys. Rev. Lett.109, 181602 (2012)

    work page 2012

  22. [22]

    E. S. Fraga and A. J. Mizher, Phys. Rev. D78, 025016 (2008)

    work page 2008

  23. [23]

    Becattini, W

    F. Becattini, W. Florkowski and E. Speranza, Phys. Lett. B789, 419 (2019)

    work page 2019

  24. [24]

    S. R. de Groot, W. A. van Leeuwen, and Ch. G. van Weert,Relativistic Kinetic Theory: Prin- ciples and Applications(North-Holland Publishing Company, Amsterdam, 1974)

    work page 1974

  25. [25]

    Becattini, V

    F. Becattini, V. Chandra, L. Del Zanna and E. Grossi, Annals Phys.338, 32-49 (2013)

    work page 2013

  26. [26]

    D. Shen, J. Chen, X. G. Huang, Y. G. Ma, A. Tang and G. Wang, Research8, 0726 (2025)

    work page 2025

  27. [27]

    Tuchin, Phys

    K. Tuchin, Phys. Rev. C88, no.2, 024911 (2013)

    work page 2013

  28. [28]

    Acharyaet al.[ALICE], Phys

    S. Acharyaet al.[ALICE], Phys. Rev. C101, no.4, 044611 (2020)

    work page 2020

  29. [29]

    Bhadury, W

    S. Bhadury, W. Florkowski, A. Jaiswal, A. Kumar and R. Ryblewski, Phys. Lett. B814, 136096 (2021)

    work page 2021

  30. [30]

    W. T. Deng and X. G. Huang, Phys. Rev. C85, 044907 (2012)

    work page 2012

  31. [31]

    Ayala, D

    A. Ayala, D. De La Cruz, S. Hern´ andez-Ort´ ız, L. A. Hern´ andez and J. Salinas, Phys. Lett. B801, 135169 (2020)

    work page 2020

  32. [32]

    Navaset al.[Particle Data Group], Phys

    S. Navaset al.[Particle Data Group], Phys. Rev. D110, 030001 (2024)

    work page 2024

  33. [33]

    Gurtleret al.[QCDSF], PoSLA TTICE2008, 051 (2008)

    M. Gurtleret al.[QCDSF], PoSLA TTICE2008, 051 (2008)

    work page 2008

  34. [34]

    A. M. Badalian and Y. A. Simonov, Phys. Rev. D87, no.7, 074012 (2013)

    work page 2013

  35. [35]

    E. V. Luschevskaya, O. E. Solovjeva, O. V. Teryaev and M. S. Prokudin, EPJ Web Conf.182, 02077 (2018)

    work page 2018