Symmetry-based nonlinear fluctuating hydrodynamics in one dimension
Pith reviewed 2026-05-17 22:16 UTC · model grok-4.3
The pith
Symmetry and conservation laws determine the nonlinear fluctuating hydrodynamics equations in one dimension, producing a KPZ fixed point with dynamical exponent 3/2 for sound and heat modes.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
A symmetry-based formulation yields the nonlinear fluctuating hydrodynamics equations for one-dimensional systems directly from symmetry and conservation principles, ensuring consistency with thermalization and producing a KPZ-type fixed point with dynamical exponent z=3/2 for both sound and heat modes, with simulations confirming closeness to the Prahofer-Spohn scaling function.
What carries the argument
Symmetry-based derivation of the nonlinear fluctuating hydrodynamics equations, analyzed via dynamic renormalization group to locate the KPZ fixed point.
If this is right
- The dynamical exponent z=3/2 governs scaling for both sound and heat modes.
- Fluctuations of both modes approach the universal Prahofer-Spohn scaling function.
- Transport and fluctuation phenomena become universal across systems with different microscopic details.
- The description remains consistent with thermalization in the nonequilibrium steady state.
Where Pith is reading between the lines
- The same symmetry arguments could organize fluctuating hydrodynamics in other one-dimensional systems obeying similar conservation laws.
- Extensions to weakly perturbed higher-dimensional cases might reveal when the z=3/2 scaling persists or crosses over.
- Direct comparison of measured correlation functions in lattice models against the derived equations could test the independence from interaction specifics.
Load-bearing premise
The hydrodynamic equations for generic homogeneous nearest-neighbor interactions can be derived solely from symmetry and conservation principles while remaining fully consistent with thermalization and independent of microscopic details.
What would settle it
Observation of a dynamical exponent other than 3/2 for the sound or heat modes in numerical simulations or physical experiments on one-dimensional systems with nearest-neighbor interactions.
Figures
read the original abstract
We present a symmetry-based formulation of nonlinear fluctuating hydrodynamics (NFH) for one-dimensional many-particle systems with generic homogeneous nearest-neighbor interactions. We derive the hydrodynamic equations solely from symmetry and conservation principles, ensuring full consistency with thermalization. Using the dynamic renormalization group, we identify a KPZ-type fixed point, characterized by the dynamical exponent $z=3/2$ for both the sound and heat modes. Extensive numerical simulations of the derived NFH equations confirm this exponent and further reveal that both modes are close to the universal KPZ scaling function, the Prahofer-Spohn function. These findings establish a unified, symmetry-based framework for understanding universal transport and fluctuation phenomena in one-dimensional nonequili brium systems, independent of microscopic details.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents a symmetry-based formulation of nonlinear fluctuating hydrodynamics (NFH) for one-dimensional many-particle systems with generic homogeneous nearest-neighbor interactions. The hydrodynamic equations are derived solely from symmetry and conservation principles while ensuring consistency with thermalization. Dynamic renormalization group analysis identifies a KPZ-type fixed point with dynamical exponent z=3/2 for both sound and heat modes. Numerical simulations of the derived NFH equations are used to confirm this exponent and to show that both modes approach the universal KPZ scaling function (Prahofer-Spohn function).
Significance. If the central claims hold, the work supplies a unified, parameter-free framework for universal transport and fluctuations in one-dimensional nonequilibrium systems that is independent of microscopic details. It would extend KPZ universality to both sound and heat modes within a symmetry-derived hydrodynamic description and strengthen the link between conservation laws and dynamical scaling in low-dimensional systems.
major comments (2)
- [Derivation of the NFH equations] The central derivation asserts that the complete set of NFH equations, including stochastic noise terms and their correlators, follows from symmetry and conservation alone. However, consistency with thermalization requires that noise amplitudes satisfy the fluctuation-dissipation theorem and match equilibrium susceptibilities (compressibility, specific heat). The manuscript does not explicitly demonstrate how these amplitudes are fixed without additional thermodynamic input, which is the load-bearing step for the claimed independence from microscopic details.
- [Dynamic renormalization group analysis] The DRG analysis identifies the KPZ fixed point with z=3/2 for the heat mode on the basis of the nonlinearities and noise strengths obtained in the symmetry derivation. If the noise correlators are not rigorously constrained by symmetry alone, the assignment of the universality class for the heat mode rests on an assumption that requires explicit verification, for example by showing that the noise matrix is determined solely by the same symmetry constraints used for the deterministic terms.
minor comments (2)
- [Abstract] The abstract contains a typographical error: 'nonequili brium' should read 'nonequilibrium'.
- [Numerical simulations] The description of the numerical simulations would benefit from additional detail on integration scheme, system sizes, boundary conditions, and the precise procedure used to extract and compare scaling functions with the Prahofer-Spohn distribution.
Simulated Author's Rebuttal
We thank the referee for their detailed and constructive report. We address each major comment below and have made revisions to the manuscript to clarify the points raised.
read point-by-point responses
-
Referee: [Derivation of the NFH equations] The central derivation asserts that the complete set of NFH equations, including stochastic noise terms and their correlators, follows from symmetry and conservation alone. However, consistency with thermalization requires that noise amplitudes satisfy the fluctuation-dissipation theorem and match equilibrium susceptibilities (compressibility, specific heat). The manuscript does not explicitly demonstrate how these amplitudes are fixed without additional thermodynamic input, which is the load-bearing step for the claimed independence from microscopic details.
Authors: We appreciate the referee pointing out the need for explicit demonstration. The symmetry and conservation laws determine the form of both the deterministic currents and the noise terms. To ensure consistency with thermalization, the noise strengths are fixed by the fluctuation-dissipation theorem, which relates them to the equilibrium susceptibilities. In the revised manuscript, we have added a detailed explanation in Section II showing how these amplitudes are determined solely from the thermodynamic relations implied by the conservation laws and symmetries, without reference to specific microscopic interactions. The susceptibilities themselves are part of the hydrodynamic description and do not depend on microscopic details beyond the symmetry class. This addresses the concern while preserving the independence from microscopic details for the universal scaling. revision: yes
-
Referee: [Dynamic renormalization group analysis] The DRG analysis identifies the KPZ fixed point with z=3/2 for the heat mode on the basis of the nonlinearities and noise strengths obtained in the symmetry derivation. If the noise correlators are not rigorously constrained by symmetry alone, the assignment of the universality class for the heat mode rests on an assumption that requires explicit verification, for example by showing that the noise matrix is determined solely by the same symmetry constraints used for the deterministic terms.
Authors: We agree that explicit verification is important. The noise matrix is determined by the same symmetry constraints as the deterministic terms, augmented by the fluctuation-dissipation relation required for thermalization. In the revised version, we have included an explicit calculation demonstrating that the noise correlators follow directly from these symmetry-based constraints and the equilibrium conditions. This confirms that no additional assumptions are needed beyond those used for the deterministic part, thereby rigorously supporting the KPZ fixed point for the heat mode as well. revision: yes
Circularity Check
Symmetry-conservation derivation of NFH equations stands independent of fitted parameters or self-citation chains
full rationale
The paper derives the NFH equations from symmetry and conservation laws for generic nearest-neighbor interactions, then applies dynamic renormalization group analysis to recover the known KPZ fixed point (z=3/2) for sound and heat modes. No load-bearing step reduces by construction to a fitted input, self-citation, or ansatz smuggled from prior work; the noise terms are stated to ensure thermalization consistency without explicit parameter fitting to the target exponents. Numerical simulations of the derived equations provide external confirmation of the scaling. The derivation chain remains self-contained against external benchmarks, with the KPZ identification serving as an application rather than a redefinition of inputs.
Axiom & Free-Parameter Ledger
axioms (2)
- ad hoc to paper Hydrodynamic equations for 1D systems with generic homogeneous nearest-neighbor interactions can be derived solely from symmetry and conservation principles.
- domain assumption The resulting equations remain fully consistent with thermalization.
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We derive the hydrodynamic equations solely from symmetry and conservation principles... Using the dynamic renormalization group, we identify a KPZ-type fixed point, characterized by the dynamical exponent z=3/2
-
IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the NFH equations themselves have not yet been numerically verified... symmetry-based formulation... independent of microscopic details
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
A more detailed investigation, including extensive simulations, is left for future work
When the symmetry-based NFH is considered with- out imposing the equilibrium condition, the RG analysis yields unstable fixed points, possibly reflecting anoma- lous thermalization behavior in the underlying Hamilto- nian dynamics. A more detailed investigation, including extensive simulations, is left for future work. This work provides a crucial step to...
-
[2]
D. Bandurin, I. Torre, R. K. Kumar, M. Ben Shalom, A. Tomadin, A. Principi, G. Auton, E. Khestanova, K. Novoselov, I. Grigorieva,et al., Negative local resis- tance caused by viscous electron backflow in graphene, Science351, 1055 (2016)
work page 2016
- [3]
-
[4]
P. J. Moll, P. Kushwaha, N. Nandi, B. Schmidt, and A. P. Mackenzie, Evidence for hydrodynamic electron flow in pdcoo2, Science351, 1061 (2016)
work page 2016
-
[5]
R. Krishna Kumar, D. Bandurin, F. Pellegrino, Y. Cao, A. Principi, H. Guo, G. Auton, M. Ben Shalom, L. Pono- marenko, G. Falkovich,et al., Superballistic flow of vis- cous electron fluid through graphene constrictions, Na- ture Physics13, 1182 (2017)
work page 2017
-
[6]
S. Lee, D. Broido, K. Esfarjani, and G. Chen, Hydrody- namic phonon transport in suspended graphene, Nature communications6, 6290 (2015)
work page 2015
-
[7]
J. A. Sulpizio, L. Ella, A. Rozen, J. Birkbeck, D. J. Perello, D. Dutta, M. Ben-Shalom, T. Taniguchi, K. Watanabe, T. Holder,et al., Visualizing poiseuille flow of hydrodynamic electrons, Nature576, 75 (2019)
work page 2019
-
[8]
O. A. Castro-Alvaredo, B. Doyon, and T. Yoshimura, Emergent Hydrodynamics in Integrable Quantum Sys- tems Out of Equilibrium, Phys. Rev. X6, 041065 (2016)
work page 2016
-
[9]
P. Ruggiero, P. Calabrese, B. Doyon, and J. Dubail, Quantum Generalized Hydrodynamics, Phys. Rev. Lett. 124, 140603 (2020)
work page 2020
-
[10]
Spohn, Generalized Gibbs ensembles of the classical Toda chain, J
H. Spohn, Generalized Gibbs ensembles of the classical Toda chain, J. Stat. Phys. , https://doi.org/10.1007/s10955 (2019)
-
[11]
M. Schemmer, I. Bouchoule, B. Doyon, and J. Dubail, Generalized Hydrodynamics on an Atom Chip, Phys. Rev. Lett.122, 090601 (2019)
work page 2019
-
[12]
van Beijeren, Exact Results for Anomalous Transport in One-Dimensional Hamiltonian Systems, Phys
H. van Beijeren, Exact Results for Anomalous Transport in One-Dimensional Hamiltonian Systems, Phys. Rev. Lett.108, 180601 (2012)
work page 2012
-
[13]
H. Spohn, Nonlinear fluctuating hydrodynamics for an- harmonic chains, Journal of Statistical Physics154, 1191 (2014)
work page 2014
-
[14]
H. Spohn, Fluctuating hydrodynamics approach to equi- librium time correlations for anharmonic chains, inTher- mal Transport in Low Dimensions: From Statistical Physics to Nanoscale Heat Transfer(Springer, 2016) pp. 107–158
work page 2016
-
[15]
S. G. Das, A. Dhar, K. Saito, C. B. Mendl, and H. Spohn, Numerical test of hydrodynamic fluctuation theory in 6 the Fermi-Pasta-Ulam chain, Phys. Rev. E90, 012124 (2014)
work page 2014
-
[16]
M. Kulkarni, D. A. Huse, and H. Spohn, Fluctuat- ing hydrodynamics for a discrete Gross-Pitaevskii equa- tion: Mapping onto the Kardar-Parisi-Zhang universality class, Phys. Rev. A92, 043612 (2015)
work page 2015
- [17]
-
[18]
J. De Nardis, S. Gopalakrishnan, and R. Vasseur, Non- linear fluctuating hydrodynamics for kardar-parisi-zhang scaling in isotropic spin chains, Physical review letters 131, 197102 (2023)
work page 2023
-
[19]
K. Hiura, Microscopic derivation of nonlinear fluctuating hydrodynamics for crystalline solid, Physical Review E 108, 054101 (2023)
work page 2023
- [20]
-
[21]
H. Spohn and G. Stoltz, Nonlinear fluctuating hydrody- namics in one dimension: the case of two conserved fields, Journal of Statistical Physics160, 861 (2015)
work page 2015
-
[22]
A. Das, K. Damle, A. Dhar, D. A. Huse, M. Kulkarni, C. B. Mendl, and H. Spohn, Nonlinear fluctuating hy- drodynamics for the classical xxz spin chain, Journal of Statistical Physics180, 238 (2020)
work page 2020
- [23]
-
[24]
S. Gopalakrishnan, E. McCulloch, and R. Vasseur, Non- gaussian diffusive fluctuations in dirac fluids, Proceedings of the National Academy of Sciences121, e2403327121 (2024)
work page 2024
-
[25]
H. Nishikawa and K. Saito, Energy diffusion in the long- range interacting spin systems, Physical Review Letters 135, 147102 (2025)
work page 2025
-
[26]
See Supplemental Material for additional details
-
[27]
D. Forster, D. R. Nelson, and M. J. Stephen, Large- distance and long-time properties of a randomly stirred fluid, Phys. Rev. A16, 732 (1977)
work page 1977
-
[28]
L. M. Smith and S. L. Woodruff, Renormalization-group analysis of turbulence, Annual review of fluid mechanics 30, 275 (1998)
work page 1998
-
[29]
J. B. Bell, A. Nonaka, A. L. Garcia, and G. Eyink, Ther- mal fluctuations in the dissipation range of homogeneous isotropic turbulence, Journal of fluid mechanics939, A12 (2022)
work page 2022
- [30]
-
[31]
L. Gosteva, M. Brachet, and L. Canet, Emergent dynam- ical scaling in the inviscid limit of 3D stochastic navier- stokes equation with thermal noise, arXiv:2507.05811 (2025)
- [32]
-
[33]
I. Srivastava, D. R. Ladiges, A. J. Nonaka, A. L. Garcia, and J. B. Bell, Staggered scheme for the compressible fluctuating hydrodynamics of multispecies fluid mixtures, Physical review. E107, 015305 (2023)
work page 2023
-
[34]
L. Landau and E. Lifshitz, Fluid mechanics. volume 6 of course of theoretical physics, 2nd english ed. translated from the russian by jb sykes, wh reid (1987)
work page 1987
-
[35]
Effective Field Theory and the Fermi Surface
J. Polchinski, Effective field theory and the fermi surface, (1992), arXiv:hep-th/9210046 [hep-th]
work page internal anchor Pith review Pith/arXiv arXiv 1992
-
[36]
D. B. Kaplan, Five lectures on effective field theory, (2005), arXiv:nucl-th/0510023 [nucl-th]
work page internal anchor Pith review Pith/arXiv arXiv 2005
- [37]
-
[38]
Lepri (Ed.),Thermal Transport in Low Dimensions
S. Lepri (Ed.),Thermal Transport in Low Dimensions. From Statistical Physics to Nanoscale Heat Transfer, Vol. Lecture Notes in Physics Vol. 921 (Springer-Verlag, Berlin, 2016)
work page 2016
-
[39]
G. Benenti, D. Donadio, S. Lepri, and R. Livi, Non- fourier heat transport in nanosystems, La Rivista del Nuovo Cimento46, 105 (2023)
work page 2023
-
[40]
C. W. Chang, D. Okawa, H. Garcia, A. Majumdar, and A. Zettl, Breakdown of fourier’s law in nanotube thermal conductors, Physical review letters101, 075903 (2008)
work page 2008
-
[41]
X. Xu, L. F. C. Pereira, Y. Wang, J. Wu, K. Zhang, X. Zhao, S. Bae, C. Tinh Bui, R. Xie, J. T. L. Thong, B. H. Hong, K. P. Loh, D. Donadio, B. Li, and B. ¨Ozyilmaz, Length-dependent thermal conductivity in suspended single-layer graphene, Nature communications 5, 3689 (2014)
work page 2014
- [42]
-
[43]
M. Pr¨ ahofer and H. Spohn, Exact scaling functions for one-dimensional stationary kpz growth, Journal of sta- tistical physics115, 255 (2004)
work page 2004
-
[44]
C. B. Mendl and H. Spohn, Dynamic correlators of fermi- pasta-ulam chains and nonlinear fluctuating hydrody- namics, Physical review letters111, 230601 (2013)
work page 2013
-
[45]
C. B. Mendl and H. Spohn, Equilibrium time-correlation functions for one-dimensional hard-point systems, Phys- ical Review E90, 012147 (2014)
work page 2014
-
[46]
Zwanzig, Memory Effects in Irreversible Thermody- namics, Phys
R. Zwanzig, Memory Effects in Irreversible Thermody- namics, Phys. Rev.124, 983 (1961)
work page 1961
-
[47]
D. N. Zubarev and V. G. Morozov, Statistical mechanics of nonlinear hydrodynamic fluctuations, Physica A120, 411 (1983)
work page 1983
-
[48]
R. Kubo, M. Toda, and N. Hashitsume,Statisti- cal Physics II: Nonequilibrium Statistical Mechanics (Springer-Verlag, Berlin, 2012)
work page 2012
-
[49]
P. C. Martin, E. D. Siggia, and H. A. Rose, Statistical dynamics of classical systems, Physical Review A8, 423 (1973)
work page 1973
-
[50]
H.-K. Janssen, On a lagrangean for classical field dynam- ics and renormalization group calculations of dynamical critical properties, Zeitschrift f¨ ur Physik B Condensed Matter23, 377 (1976)
work page 1976
-
[51]
de Dominicis, Technics of field renormalization and dynamics of critical phenomena, inJ
C. de Dominicis, Technics of field renormalization and dynamics of critical phenomena, inJ. Phys.(Paris), Col- loq.;(France), Vol. 1 (1976)
work page 1976
-
[52]
C. De Dominicis, Dynamics as a substitute for replicas in systems with quenched random impurities, Physical Review B18, 4913 (1978)
work page 1978
-
[53]
F. BalboaUsabiaga, J. B. Bell, R. Delgado-Buscalioni, A. Donev, T. G. Fai, B. E. Griffith, and C. S. Peskin, Staggered schemes for fluctuating hydrodynamics, Mul- tiscale modeling & simulation10, 1369 (2012)
work page 2012
- [54]
- [55]
- [56]
-
[57]
Note thatϕ α = P b Rαbub, whereu b is the deviation from the average value, and hence R dxϕα(x, t) = 0 holds identically
-
[58]
J. B. Bell, A. L. Garcia, and S. A. Williams, Numerical methods for the stochastic landau-lifshitz navier-stokes equations, Physical Review E76, 016708 (2007)
work page 2007
-
[59]
R. Yoneda and K. Harada, Neural network approach to scaling analysis of critical phenomena, Physical Review E107, 044128 (2023)
work page 2023
-
[60]
See Supple- mental Material for details
We have confirmed this point for the one-component Burgers equation for finite sound velocity. See Supple- mental Material for details
-
[61]
SYMMETRY-BASED NONLINEAR FLUCTUATING HYDRODYNAMICS IN ONE DIMENSION
The simulation data is available on GitLab at https://isspns-gitlab.issp.u-tokyo.ac.jp/ nakano35255/comp_fluct_hydro.git. 8 END MATTER Appendix A: Explicit expressions for the symmetry- based NFH equations.—We present explicit expressions for the parameters in the symmetry-based NFH equa- tions. See the SM for the details [25]. From the time- reversal sym...
-
[62]
Remarks on the sound velocities in the RG
We thus obtain H2 = H2 11 0 (a 3/a0)H2 11 0H 2 22 0 (a3/a0)H2 11 0 (a 2 3/a2 0)H2 11 ,(S39) H3 = 0 (1/a 0)H2 11 0 (1/a0)H2 11 0 (a 3/a2 0)H2 11 0 (a 3/a2 0)H2 11 0 .(S40) B. Special case with the space-inversion symmetry Here, we consider the special case where the Hamiltonian has the space-inversion symmetry,i→N−i. This case is special, s...
-
[63]
Advection term [αc sϕα i+1/2]: This term is approximated by αcsϕα i+1/2 =αc s ϕα i+1 +ϕ α i 2 .(S166)
-
[64]
Diffusion term [D α(∂xϕα)i+1/2]: This term is approximated by Dα(∂xϕα)i+1/2 =D α ϕα i+1 −ϕ α i auv .(S167)
-
[65]
The semi-discrete equations Eq
Nonlinear term [G α βγ(ϕβϕγ)i+1/2]: This term is approximated by Gα βγ(ϕβϕγ)i+1/2 =G α βγ ϕβ i ϕγ i+1 +ϕ β i+1ϕγ i 12 + ϕβ i ϕγ i +ϕ β i+1ϕγ i+1 6 ! .(S168) Importantly, in the absence of noise, this formulation strictly conserves the quantity P α=+,−,0(ϕα)2 [54]. The semi-discrete equations Eq. (S164) form a system of stochastic ordinary differential equ...
work page 2048
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.