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Hydrodynamic fluctuations and topological susceptibility in chiral magnetohydrodynamics

by Arpit Das, Nabil Iqbal, Napat Poovuttikul

Submission summary

Authors (as registered SciPost users): Arpit Das
Submission information
Preprint Link:  (pdf)
Date submitted: 2024-05-24 08:22
Submitted by: Das, Arpit
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
  • High-Energy Physics - Theory
  • High-Energy Physics - Phenomenology
Approach: Theoretical


Chiral magnetohydrodynamics is devoted to understanding the late-time and long-distance behavior of a system with an Adler-Bell-Jackiw anomaly at finite temperatures. The non-conservation of the axial charge is determined by the topological density $\vec{E} \cdot \vec{B}$; in a classical hydrodynamic description this decay rate can be suppressed by tuning the background magnetic field to zero. However it is in principle possible for thermal fluctuations of $\vec{E} \cdot \vec{B}$ to result in a non-conservation of the charge even at vanishing $B$-field; this would invalidate the classical hydrodynamic effective theory. We investigate this by computing the real-time susceptibility of the topological density at one-loop level in magnetohydrodynamic fluctuations, relating its low-frequency limit to the decay rate of the axial charge. We find that the frequency-dependence of this susceptibility is sufficiently soft as to leave the axial decay rate unaffected, validating the classical hydrodynamic description. We show that the susceptibility contains non-analytic frequency-dependence which is universally determined by hydrodynamic data. We comment briefly on possible connections to the recent formulation of the ABJ anomaly in terms of non-invertible symmetry.

Author indications on fulfilling journal expectations

  • Provide a novel and synergetic link between different research areas.
  • Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
  • Detail a groundbreaking theoretical/experimental/computational discovery
  • Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
In refereeing

Reports on this Submission

Anonymous Report 1 on 2024-7-19 (Invited Report)


1- Concretely identified problem and its resolution.
2- Well-written and clearly presented.
3- Interesting albeit technical results for the target audience in the field.


1- The results are quite technical in nature, but sufficient effort has been made to identify certain qualitative features.
2- The results are interesting as a consistency check for chiral magnetohydrodynamics, but do not seem to have any direct applications otherwise.


The paper discusses one-loop correction to the susceptibility of topological density in chiral magnetohydrodynamics. The authors are particularly interested in the behaviour at zero magnetic field. The authors note that while classically the topological susceptibility vanishes at zero magnetic field, the same is not guaranteed to hold in the presence of loop corrections. The authors find that the one-loop corrections do indeed vanish as the magnetic field is taken to zero. This is an interesting consistency check for the validity of classical chiral magnetohydrodynamics at late times and long distances. I find the results presented in the paper quite interesting and well-presented and can recommend it for publication in SciPost Physics.


Publish (meets expectations and criteria for this Journal)

  • validity: high
  • significance: ok
  • originality: high
  • clarity: high
  • formatting: excellent
  • grammar: excellent

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