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Non-stationary current fluctuations in 1D boundary-driven diffusive systems via Macroscopic Fluctuation Theory

T0 review · 2 major / 2 minor · reviewed 2026-07-01 · grok-4.3

Pith's one-line read Macroscopic Fluctuation Theory yields exact current variance during relaxation in one-dimensional boundary-driven diffusive systems.

desk verdict MFT gets pushed to relaxation dynamics here with exact variance and CGF results, but only for constant diffusion and a couple of solvable models. read the letter →

arxiv 2605.27275 v2 pith:FTHQTHWH submitted 2026-05-26 cond-mat.stat-mech

classification cond-mat.stat-mech
keywords MacroscopicFluctuationTheorycurrentfluctuationsnon-stationaryprocessesdiffusivesystemsboundary-drivenrelaxationdynamicsReflectiveBrownianMotion
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

The paper applies Macroscopic Fluctuation Theory to the time-dependent relaxation of one-dimensional diffusive systems driven by particle reservoirs at the boundaries. It obtains an exact expression for the current variance when the diffusion coefficient is constant (with arbitrary mobility) and the cumulant generating function for current in Reflective Brownian Motion. These derivations establish that fluctuations in the non-steady regime, as the system approaches a steady state, fall within the quantitative reach of the MFT framework.

What carries the argument

Macroscopic Fluctuation Theory extended to time-dependent relaxation, used to compute exact current statistics.

What would settle it

Measure or simulate the time-dependent current variance in a one-dimensional diffusive system with constant diffusion during relaxation and compare it to the MFT-derived formula; systematic deviation would show the extension fails.

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Extended reading notes

Core claim

Applying Macroscopic Fluctuation Theory to the relaxation process produces an exact current variance for constant diffusion coefficient and arbitrary mobility, together with the cumulant generating function for Reflective Brownian Motion, showing that non-steady current fluctuations are quantitatively described by MFT.

Load-bearing premise

Macroscopic Fluctuation Theory, developed for steady states, extends directly to the relaxation regime and still produces exact closed-form results for constant diffusion coefficient.

Editorial extensions

If this is right

  • Current variance follows a closed-form time dependence throughout the approach to steady state.
  • The cumulant generating function for current is obtained exactly in Reflective Brownian Motion.
  • Non-steady fluctuations are captured quantitatively by the same MFT equations used for steady states.
  • The framework applies to arbitrary mobility when diffusion is constant.

Reading between the lines

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

  • Time-resolved current measurements in mesoscopic systems could test the formulas before steady state is reached.
  • The constant-diffusion restriction suggests checking whether similar exact results hold when diffusion varies weakly with density.
  • The derivations may generalize to other boundary-driven transport models once the mobility-diffusion relation is fixed.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 2 minor

Summary. The paper applies Macroscopic Fluctuation Theory (MFT) to the relaxation dynamics of 1D boundary-driven diffusive systems coupled to reservoirs. It claims exact closed-form derivations of the time-dependent current variance for constant diffusion coefficient D and arbitrary mobility, together with the cumulant generating function for the current in Reflective Brownian Motion (RBM). The central result is that non-stationary current fluctuations during relaxation are quantitatively captured by the MFT framework without additional approximations beyond the standard hydrodynamic scaling.

Significance. If the derivations hold, the work provides a concrete extension of MFT from steady states to the transient regime for a solvable class of models. The exact variance and CGF expressions constitute falsifiable predictions that can be tested against microscopic simulations or exact solutions in the constant-D limit, strengthening the case for MFT as a tool for non-stationary fluctuations.

major comments (2)
  1. [§3] §3 (or the section deriving the variance): the reduction of the MFT action to a closed-form variance for arbitrary mobility appears to rely on the specific choice of constant D; it is unclear whether the same steps remain exact when D is position-dependent, which would limit the generality of the claim that the result holds for 'arbitrary mobility'.
  2. [§4] The derivation of the CGF for RBM (likely §4): the boundary conditions and the reflective nature of the process must be shown to map exactly onto the MFT saddle-point equations without residual boundary terms; the manuscript should explicitly verify that the time-dependent optimal density and current profiles satisfy the Euler-Lagrange equations with the reflective constraint.
minor comments (2)
  1. The abstract and introduction should clarify the precise hydrodynamic scaling limit under which the MFT equations are applied to the relaxation process.
  2. Notation for the mobility function and the time-dependent current should be introduced consistently before the first derivation.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive assessment and the detailed comments on our manuscript. We address each major comment below.

read point-by-point responses
  1. Referee: [§3] §3 (or the section deriving the variance): the reduction of the MFT action to a closed-form variance for arbitrary mobility appears to rely on the specific choice of constant D; it is unclear whether the same steps remain exact when D is position-dependent, which would limit the generality of the claim that the result holds for 'arbitrary mobility'.

    Authors: We agree with the referee that the closed-form expression for the time-dependent current variance is derived under the assumption of constant diffusion coefficient D. The manuscript explicitly states this restriction (see abstract and §3), and the claim of arbitrary mobility applies only within the constant-D class. We do not claim or derive the same closed-form result for position-dependent D, where the MFT action reduction does not close in the same manner. The scope of the paper is therefore accurately delimited, and no revision is required. revision: no

  2. Referee: [§4] The derivation of the CGF for RBM (likely §4): the boundary conditions and the reflective nature of the process must be shown to map exactly onto the MFT saddle-point equations without residual boundary terms; the manuscript should explicitly verify that the time-dependent optimal density and current profiles satisfy the Euler-Lagrange equations with the reflective constraint.

    Authors: We thank the referee for this suggestion. In the revised version we will add an explicit verification step showing that the time-dependent optimal density and current profiles obtained from the MFT saddle-point equations for Reflective Brownian Motion satisfy the Euler-Lagrange equations together with the reflective boundary conditions, confirming the absence of residual boundary terms. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity in derivation chain

full rationale

The paper applies MFT to derive exact closed-form expressions for current variance (constant D, arbitrary mobility) and CGF for RBM in the relaxation regime. No load-bearing steps reduce by construction to inputs, fitted parameters renamed as predictions, or self-citation chains that substitute for independent derivation. The results are positioned as following directly from the MFT framework under the stated solvability conditions for this restricted class of systems, with no evidence of self-definitional equivalence or smuggling of ansatzes via prior work.

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

Abstract-only access prevents identification of specific free parameters, axioms, or invented entities; no details on fitting, background assumptions, or new postulated quantities are provided.

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Cite this review

Pith. "Pith review of Non-stationary current fluctuations in 1D boundary-driven diffusive systems via Macroscopic Fluctuation Theory." pith.science (2026). https://pith.science/paper/FTHQTHWH

@misc{pith2026260527275,
  author       = {Pith},
  title        = {Pith review of: Non-stationary current fluctuations in 1D boundary-driven diffusive systems via Macroscopic Fluctuation Theory},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/FTHQTHWH}},
  note         = {Machine review of arXiv:2605.27275}
}
read the original abstract

While Macroscopic Fluctuation Theory (MFT) has been highly successful in analyzing non-equilibrium steady states, its application to non-steady-state processes remains limited. In this study, we apply MFT to the relaxation process of one-dimensional boundary-driven diffusive systems coupled to particle reservoirs at both ends. We exactly derive the current variance for systems with a constant diffusion coefficient and arbitrary mobility, as well as the cumulant generating function for the current in Reflective Brownian Motion (RBM). Our results demonstrate that non-steady current fluctuations during the approach to a steady state can be quantitatively described within the MFT framework.

Figures

Figures reproduced from arXiv: 2605.27275 by the authors.

Figure 1
Figure 1. An example of the time evo￾lution of the expected integrated cur￾rent ⟨QT ⟩ in boundary-driven RBM. QT crosses over from O( √ T) growth to linear O(T) growth in time. Macroscopic Fluctuation Theory (MFT), recently proposed by Bertini et al., has emerged as a pow￾erful theoretical framework for analyzing large deviations of density and current fields in these diffusive systems [14, 15]. MFT describes fluctuations in … view at source ↗
Figure 2
Figure 2. (a)Calculated results for the integrated current variance [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. An example of RBM trajectories The boundary behavior is defined analogously to the stochastic lattice gases introduced in Section 2. The system is connected to two particle reservoirs: a reservoir L with density ρL at the left boundary (x = 0) and a reservoir R with density ρR at the right boundary (x = L). At the left reservoir, particles are injected at rate a and extracted at rate c. Similarly, at the right reser… view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: Integrated current with param￾eters L = 5, ρL = 0.8, ρR = 0.2, ρ¯ = 0.5, A = B = 10 The integrated current initially scales as O(T) before crossing over to O( √ T) at T ∼ ρ 2 L A2 . It even￾tually returns to O(T) scaling at T ∼ L 2 at the diffusive time scale. The marg…
Figure 5
Figure 5. Figure 5: Large deviation function I(q) for the annealed initial condition, obtained via the Legendre transformation of the SCGF in (4.17). The plots illustrate the dependence on the boundary cou￾pling strengths (A, B), comparing the case (1, 1), (10, 10) and (100, 100). Other p…
Figure 6
Figure 6. Figure 6: The plots compare the LDFs under an￾nealed and quenched initial conditions across three distinct scaling regimes: (a)the initial O(T) regime at t = 0.008, (b)the intermediate diffusive O( √ T) regime at t = 1, (c)O(T) steady-state regime at t = 15. Under the parameters…
Figure 7
Figure 7. Figure 7: Calculated results for the large deviation function from Legendre trans￾formation of (4.17) with parameters L = 5, ρL = 2.0, ρR = 0.5, ρ¯ = 1.25. (at t = 0.008, 1, 15) Consistency with previous research In this section, we verify whether the current SCGF for the finite…

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Forward citations

Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Nonisospectral Integrability and Exact Current Fluctuations in the Two-Dimensional SSEP

    cond-mat.stat-mech 2026-08 conditional novelty 8.0 of 10

    The scaled cumulant generating function for annealed current fluctuations across a disk in the two-dimensional SSEP is obtained in closed form via a nonisospectral integrable reduction.

  2. An integrable approach to macroscopic fluctuation theory for the multispecies SSEP

    cond-mat.stat-mech 2026-06 conditional novelty 7.0 of 10

    Multispecies MFT saddle-point equations for SSEP are integrable and solved via inverse scattering to recover the current fluctuation cumulant generating function for arbitrary species number.

Reference graph

Works this paper leans on

44 extracted references · 44 canonical work pages · cited by 2 Pith papers

  1. [1]

    Cumulants and large deviations of the current through non-equilibrium steady states,

    T. Bodineau and B. Derrida, “Cumulants and large deviations of the current through non-equilibrium steady states,”Comptes Rendus. Physique, vol. 8, pp. 540–555, June 2007

  2. [2]

    Non-equilibrium steady states: fluctuations and large deviations of the density and of the current,

    B. Derrida, “Non-equilibrium steady states: fluctuations and large deviations of the density and of the current,”Journal of Statistical Mechanics: Theory and Experiment, vol. 2007, p. P07023, July 2007

  3. [3]

    Towards a Nonequilibrium Thermodynamics: A Self-Contained Macroscopic Description of Driven Diffusive Systems,

    L. Bertini, A. De Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Towards a Nonequilibrium Thermodynamics: A Self-Contained Macroscopic Description of Driven Diffusive Systems,”Journal of Statistical Physics, vol. 135, pp. 857–872, June 2009

  4. [4]

    From Fluctuations in Hydrodynamics to Nonequilibrium Thermodynamics,

    G. Jona-Lasinio, “From Fluctuations in Hydrodynamics to Nonequilibrium Thermodynamics,” Progress of Theoretical Physics Supplement, vol. 184, pp. 262–275, 2010

  5. [5]

    Lecture notes on large deviations in non-equilibrium diffusive systems,

    B. Derrida, “Lecture notes on large deviations in non-equilibrium diffusive systems,”SciPost Physics Lecture Notes, p. 106, Oct. 2025

  6. [6]

    Interaction of Markov processes,

    F. Spitzer, “Interaction of Markov processes,”Advances in Mathematics, vol. 5, pp. 246–290, Oct. 1970

  7. [7]

    Diffusion with “collisions

    T. E. Harris, “Diffusion with “collisions” between particles,”Journal of Applied Probability, vol. 2, pp. 323–338, Dec. 1965

  8. [8]

    Current Fluctuations in Nonequilibrium Diffusive Systems: An Ad- ditivity Principle,

    T. Bodineau and B. Derrida, “Current Fluctuations in Nonequilibrium Diffusive Systems: An Ad- ditivity Principle,”Physical Review Letters, vol. 92, p. 180601, May 2004

Show all 44 references
  1. [9]

    Non Equilibrium Current Fluctuations in Stochastic Lattice Gases,

    L. Bertini, A. D. Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Non Equilibrium Current Fluctuations in Stochastic Lattice Gases,”Journal of Statistical Physics, vol. 123, pp. 237–276, Apr. 2006

  2. [10]

    Dynamical Ensembles in Nonequilibrium Statistical Mechanics,

    G. Gallavotti and E. G. D. Cohen, “Dynamical Ensembles in Nonequilibrium Statistical Mechanics,” Physical Review Letters, vol. 74, pp. 2694–2697, Apr. 1995. 18

  3. [11]

    A Gallavotti–Cohen-Type Symmetry in the Large Deviation Func- tional for Stochastic Dynamics,

    J. L. Lebowitz and H. Spohn, “A Gallavotti–Cohen-Type Symmetry in the Large Deviation Func- tional for Stochastic Dynamics,”Journal of Statistical Physics, vol. 95, pp. 333–365, Apr. 1999

  4. [12]

    Current Fluctuations of the One Dimensional Symmetric Simple Exclusion Process with Step Initial Condition,

    B. Derrida and A. Gerschenfeld, “Current Fluctuations of the One Dimensional Symmetric Simple Exclusion Process with Step Initial Condition,”Journal of Statistical Physics, vol. 136, pp. 1–15, July 2009

  5. [13]

    Current fluctuations in a semi-infinite line,

    S. Saha and T. Sadhu, “Current fluctuations in a semi-infinite line,”Journal of Statistical Mechanics: Theory and Experiment, vol. 2023, p. 073207, July 2023

  6. [14]

    Macroscopic Fluctuation Theory for Stationary Non-Equilibrium States,

    L. Bertini, A. De Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Macroscopic Fluctuation Theory for Stationary Non-Equilibrium States,”Journal of Statistical Physics, vol. 107, pp. 635– 675, May 2002

  7. [15]

    Macroscopic fluctuation theory,

    L. Bertini, A. De Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Macroscopic fluctuation theory,”Reviews of Modern Physics, vol. 87, pp. 593–636, June 2015

  8. [16]

    Statistical Dynamics of Classical Systems,

    P. C. Martin, E. D. Siggia, and H. A. Rose, “Statistical Dynamics of Classical Systems,”Physical Review A, vol. 8, pp. 423–437, July 1973

  9. [17]

    Current Fluctuations in Stochastic Lattice Gases,

    L. Bertini, A. De Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Current Fluctuations in Stochastic Lattice Gases,”Physical Review Letters, vol. 94, p. 030601, Jan. 2005

  10. [18]

    Microscopic versus macroscopic approaches to non-equilibrium systems,

    B. Derrida, “Microscopic versus macroscopic approaches to non-equilibrium systems,”Journal of Statistical Mechanics: Theory and Experiment, vol. 2011, p. P01030, Jan. 2011

  11. [19]

    Large deviations and additivity principle for the open harmonic process,

    G. Carinci, C. Franceschini, R. Frassek, C. Giardin` a, and F. Redig, “Large deviations and additivity principle for the open harmonic process,” Oct. 2023. arXiv:2307.14975 [math.PR]

  12. [20]

    On a Class of Solvable Stationary Non Equi- librium States for Mass Exchange Models,

    M. Capanna, D. Gabrielli, and D. Tsagkarogiannis, “On a Class of Solvable Stationary Non Equi- librium States for Mass Exchange Models,”Journal of Statistical Physics, vol. 191, p. 25, Feb. 2024

  13. [21]

    Exact Solution of the Macroscopic Fluctuation Theory for the Symmetric Exclusion Process,

    K. Mallick, H. Moriya, and T. Sasamoto, “Exact Solution of the Macroscopic Fluctuation Theory for the Symmetric Exclusion Process,”Physical Review Letters, vol. 129, p. 040601, July 2022

  14. [22]

    Semi-infinite Simple Exclusion Process: From Current Fluctuations to Target Survival,

    A. Grabsch, H. Moriya, K. Mallick, T. Sasamoto, and O. B´ enichou, “Semi-infinite Simple Exclusion Process: From Current Fluctuations to Target Survival,”Physical Review Letters, vol. 133, p. 117102, Sept. 2024

  15. [23]

    Large deviations of current for the symmetric simple exclusion process on a semi-infinite line and on an infinite line with a slow bond,

    K. Sharma, S. Saha, S. Jangid, and T. Sadhu, “Large deviations of current for the symmetric simple exclusion process on a semi-infinite line and on an infinite line with a slow bond,”Physical Review E, vol. 113, p. L052101, May 2026

  16. [24]

    Spohn,Large Scale Dynamics of Interacting Particles

    H. Spohn,Large Scale Dynamics of Interacting Particles. Berlin, Heidelberg: Springer, 1991

  17. [25]

    Kipnis and C

    C. Kipnis and C. Landim,Scaling Limits of Interacting Particle Systems, vol. 320 ofGrundlehren der mathematischen Wissenschaften. Berlin, Heidelberg: Springer, 1999

  18. [26]

    The large deviation approach to statistical mechanics,

    H. Touchette, “The large deviation approach to statistical mechanics,”Physics Reports, vol. 478, pp. 1–69, July 2009

  19. [27]

    Large Deviations in Single-File Diffusion,

    P. Krapivsky, K. Mallick, and T. Sadhu, “Large Deviations in Single-File Diffusion,”Physical Review Letters, vol. 113, p. 078101, Aug. 2014

  20. [28]

    Stochastic interacting particle systems out of equilibrium,

    L. Bertini, A. De Sole, D. Gabrielli, G. Jona-Lasinio, and C. Landim, “Stochastic interacting particle systems out of equilibrium,”Journal of Statistical Mechanics: Theory and Experiment, vol. 2007, p. P07014, July 2007

  21. [29]

    Exclusion Process with Slow Boundary,

    R. Baldasso, O. Menezes, A. Neumann, and R. R. Souza, “Exclusion Process with Slow Boundary,” Journal of Statistical Physics, vol. 167, pp. 1112–1142, June 2017

  22. [30]

    Non-equilibrium and stationary fluctuations for the SSEP with slow boundary,

    P. Gon¸ calves, M. Jara, O. Menezes, and A. Neumann, “Non-equilibrium and stationary fluctuations for the SSEP with slow boundary,”Stochastic Processes and their Applications, vol. 130, pp. 4326– 4357, July 2020. 19

  23. [31]

    Large Deviations in the Symmetric Simple Exclusion Process with Slow Boundaries,

    B. Derrida, O. Hirschberg, and T. Sadhu, “Large Deviations in the Symmetric Simple Exclusion Process with Slow Boundaries,”Journal of Statistical Physics, vol. 182, p. 15, Jan. 2021

  24. [32]

    Role of initial conditions in one-dimensional diffusive systems: Compressibility, hyperuniformity, and long-term memory,

    T. Banerjee, R. L. Jack, and M. E. Cates, “Role of initial conditions in one-dimensional diffusive systems: Compressibility, hyperuniformity, and long-term memory,”Physical Review E, vol. 106, p. L062101, Dec. 2022

  25. [33]

    Free Energy Functional for Nonequilibrium Systems: An Exactly Solvable Case,

    B. Derrida, J. L. Lebowitz, and E. R. Speer, “Free Energy Functional for Nonequilibrium Systems: An Exactly Solvable Case,”Physical Review Letters, vol. 87, p. 150601, Sept. 2001

  26. [34]

    Large deviations in the symmetric simple exclusion process with slow bound- aries: A hydrodynamic perspective,

    S. Saha and T. Sadhu, “Large deviations in the symmetric simple exclusion process with slow bound- aries: A hydrodynamic perspective,”SciPost Physics, vol. 17, p. 033, Aug. 2024

  27. [35]

    Fluctuations of current in nonstationary diffusive lattice gases,

    P. L. Krapivsky and B. Meerson, “Fluctuations of current in nonstationary diffusive lattice gases,” Physical Review E, vol. 86, p. 031106, Sept. 2012

  28. [36]

    Heat flow in an exactly solvable model,

    C. Kipnis, C. Marchioro, and E. Presutti, “Heat flow in an exactly solvable model,”Journal of Statistical Physics, vol. 27, pp. 65–74, Jan. 1982

  29. [37]

    Le Chatelier Principle for Out-of-Equilibrium and Boundary- Driven Systems: Application to Dynamical Phase Transitions,

    O. Shpielberg and E. Akkermans, “Le Chatelier Principle for Out-of-Equilibrium and Boundary- Driven Systems: Application to Dynamical Phase Transitions,”Physical Review Letters, vol. 116, p. 240603, June 2016

  30. [38]

    Universal Large Deviations for the Tagged Particle in Single-File Motion,

    C. Hegde, S. Sabhapandit, and A. Dhar, “Universal Large Deviations for the Tagged Particle in Single-File Motion,”Physical Review Letters, vol. 113, p. 120601, Sept. 2014

  31. [39]

    Tagged Particle in Single-File Diffusion,

    P. L. Krapivsky, K. Mallick, and T. Sadhu, “Tagged Particle in Single-File Diffusion,”Journal of Statistical Physics, vol. 160, pp. 885–925, Aug. 2015

  32. [40]

    Exact Large-Scale Correlations in Diffusive Systems with General Interactions,

    A. Grabsch, D. Venturelli, and O. B´ enichou, “Exact Large-Scale Correlations in Diffusive Systems with General Interactions,”Physical Review Letters, vol. 135, p. 137102, Sept. 2025

  33. [41]

    Macroscopic fluctuation theory of interacting Brownian particles,

    A. Grabsch, D. Venturelli, and O. B´ enichou, “Macroscopic fluctuation theory of interacting Brownian particles,”Physical Review E, vol. 113, p. 054128, May 2026

  34. [42]

    Dynamics of interacting particle systems: stochastic process and field theory,

    A. Lef` evre and G. Biroli, “Dynamics of interacting particle systems: stochastic process and field theory,”Journal of Statistical Mechanics: Theory and Experiment, vol. 2007, pp. P07024–P07024, July 2007

  35. [43]

    Langevin equation for the density of a system of interacting Langevin processes,

    D. S. Dean, “Langevin equation for the density of a system of interacting Langevin processes,” Journal of Physics A: Mathematical and General, vol. 29, p. L613, Feb. 1996

  36. [44]

    Current Fluctuations in One Dimensional Diffusive Systems with a Step Initial Density Profile,

    B. Derrida and A. Gerschenfeld, “Current Fluctuations in One Dimensional Diffusive Systems with a Step Initial Density Profile,”Journal of Statistical Physics, vol. 137, pp. 978–1000, Dec. 2009. A Derivation of(2.1)and(2.2)from(2.13)and(2.14) We show the consistency between th...

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