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On perturbation around closed exclusion processes
by Masataka Watanabe
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Submission summary
Authors (as registered SciPost users):  Masataka Watanabe 
Submission information  

Preprint Link:  https://arxiv.org/abs/2406.02675v2 (pdf) 
Date submitted:  20240814 09:08 
Submitted by:  Watanabe, Masataka 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
We derive the formula for the stationary states of particlenumber conserving exclusion processes infinitesimally perturbed by inhomogeneous adsorption and desorption. The formula not only proves but also generalises the conjecture proposed in arXiv:1711.06949 to account for inhomogeneous adsorption and desorption. As an application of the formula, we draw part of the phase diagrams of the open asymmetric simple exclusion process with and without Langmuir kinetics, correctly reproducing known results.
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List of changes
As a reply to the first referee:
Requested change 1: Thank you for encoiuraging me to do it. Rereading my manuscript, indeed this part was not very clearly written. I changed the draft so that it is selfcontained. I added a paragraph on page 5, starting from "Let us also present the strategy of the proof."
Requested change 2: This was a bad explanation of mine. We are meant to sum over (4.8) on the LHS of (4.6), so we use the fact that $\sum_{(n)_N}q_{L_0}[(n)_{N_0}]=\binom{L_0}{N_0}_q$ . Then we will get the qbinomials in the final expressions. I changed the draft accordingly, around (4.9).
Requested change 3: This is very important. Thank you! I changed some parts of the draft where I overemphasized the meanfield approximations. I also cited related papers I found, as well as Phys. Rev. E 67, 066117 (2003).
I added the following on page 3,
"One can also derive the hydrodynamic equation by separating slow diffusion modes from fast transport modes as in \cite{condmat/0302208}.
Such analysis indeed gives the correct phase diagram at large volume, even though it does not account for fluctuations and so it does not constitute algorithmic computations of physical quantities. (However see \cite{1803.06829} for the application of fluctuating hydrodynamics to an exclusion process.)"
and on page 14,
"It would also be important to justify the hydrodynamic description theoretically.
This could be either justifying the meanfield approximation or continuing the idea developed in \cite{condmat/0302208}.
In terms of the former, one could for example compute the twopoint functions perturbatively in ϵ;
If they factorise in the thermodynamic limit, the meanfield approximation is justified at least perturbatively.
In this context, it might be worthwhile to rewrite the open ASEPLK in the language of onedimensional (nonHermitian) spin chains.
The meanfield approximation can then be justified when the model flows to the free fixedpoint in the infrared.
In terms of the latter, it would be interesting to come up with a model which is stronglycoupled in the infrared, where the meanfield approximation cannot be justified but the hydrodynamic description is available \cite{1801.08952,2104.14650,2208.02124,2405.19984}."
As a reply to the second referee:
(a) Thank you! Everything should be fixed now.
(b) Indeed such a limit can be taken! For example, if we restrict to q=0 which is the simplest, one can set $\Omega_{a,b}=0$ in (4.26) to find $p_{Li+1}/p_{Li}=\alpha/\beta$. I however decided not to include this in the draft as I thought it would make the draft more complicated.
(c) This is very interesting. Let me come back to this in future followups.
(d) Additionally, I addressed the weakness by adding Appendix A, which is the physical version of the proof in the main text.
Current status:
Reports on this Submission
Report
In the revised manuscript, the requested changes 1 and 3 of my first report have been properly done by the Author.
Concerning the requested change 2, I think that there is still an inconsistency in the manuscript.
The source of this is that two conflicting normalizations are used for q[(n)_N]. Using the definition in Eq. (4.4), the sum over (n)_N gives 1. See also the sentence below Eq. (3.13).
Now in the revised manuscript, a new sentence is added above Eq. (4.9), which says that the sum is [L N]_q instead of 1. But it must be 1, if we stick to the definition of q[(n)_N] in Eq. (4.4).
If we use the definition in Eq. (4.4) (which implies a normalization to 1), then Eqs. (4.7) and (4.8) are wrong, as the ratio of binomial coefficients are missing here (the same ratios as appear in Eqs. (4.9)).
If this point is corrected, the manuscript will be suitable for publication.
Recommendation
Ask for minor revision