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Stochastic field dynamics in models of spontaneous unitarity violation
by Lotte Mertens, Matthijs Wesseling, Jasper van Wezel
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Authors (as registered SciPost users):  Jasper van Wezel 
Submission information  

Preprint Link:  scipost_202312_00001v1 (pdf) 
Date submitted:  20231201 09:53 
Submitted by:  van Wezel, Jasper 
Submitted to:  SciPost Physics Core 
Ontological classification  

Academic field:  Physics 
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Approach:  Theoretical 
Abstract
Objective collapse theories propose a solution to the quantum measurement problem by predicting deviations from Schrodinger’s equation that can be tested experimentally. A class of objective theories based on spontaneous unitarity violation was recently introduced, in which the stochastic field required for obtaining Born’s rule does not depend on the state of the system being measured. Here, we classify possible models for the stochastic field dynamics in theories of spontaneous unitarity violation. We show that for correlated stochastic dynamics, the field must be defined on a closed manifold. In two or more dimensions, it is then always possible to find stochastic dynamics yielding Born’s rule, independent of the state being measured or the correlation time of the stochastic field. We show that the models defined this way are all isomorphic to the definition on a twosphere, which we propose to be a minimal physical model for the stochastic field in models of spontaneous unitarity violation.
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Anonymous Report 1 on 202429 (Invited Report)
 Cite as: Anonymous, Report on arXiv:scipost_202312_00001v1, delivered 20240209, doi: 10.21468/SciPost.Report.8528
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esoteric topic
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Report on the paper “Stochastic Field Dynamics and Models of Spontaneous Unitary Violation”.
The manuscript represents a discussion of objective collapse theories as a solution to the quantum measurement problem. I'm not an expert in the field. But I still find the paper very well written and largely understandable, even to a nonexpert. While I do have hile I do have several suggestions for possible improvements to the paper, I nevertheless think that the paper after these improvements have been made Is certainly publishable in SciPost.
The main attractive point of the present paper, and a point which distinguishes it from many other papers on fundamental theories, is that it can actually rule out equation 10 or equation 3 as a viable model of an objective collapse theory.
Requested changes
1. If I understand it correctly. Then the idea of objective collapse theories is to model the collapse of the wave function by a stochastic nonunitary term. Augmented by a non unitary nonlinear element. This is mentioned in the abstract and also discussed on the first page and first paragraph of the right hand column. Perhaps this could be discussed a little bit further and made a little bit clearer to the nonexpert.
2.. The use of equations 2 and three should be better motivated than simply saying. These are the 2. Equations possible. A few words regarding why this is physically required or plausible would be helpful.
3. I'm slightly at a loss how exactly the requirement to adhere to Born’s rule enters in the discussion here. In particular, it is never stated what you actually have in mind regarding Born's rule and how it connects to equations 2 and 3?
4. At the beginning of Section 4 mesoscopic regime we make a connection between a violation of Bournes rule and faster than light communication. I do not see this connection. Please explain.
5. You introduce the factor B as the ratio between the coupling strengths of the stochastic noise and the nonlinear coupling. Later on you discuss this as JN relative to BJN. Why not simply use B as the relative strength? I found this confusing.
6. In the letter parts of the paper you discuss equations 9 and 10 only. But these are indeed just modified equations 2 and three. I think it would be better if you were to make a connection back to your original equations 2 and three at least. Remind the reader once in a while that it is not equations 9 and 10 that you're looking at, but really equations 2 and three.
7. In Section 5, you argue that constant J has to be weak. It would be good to have some estimate of what “weak” actually means in this context. For example, something that relates it to the strengths of \hbar or some other such fundamental constant. If that is not possible, then it would also be good to highlight why this is not possible.
8. The paper certainly represents a serious effort to discuss objective collapse theories, and I'm delighted by the many appendices that give further detail.
I have found only very few typos. But there are some. So the authors might want to have a further check.