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Analogous Hawking Radiation in Butterfly Effect
by Takeshi Morita
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Submission summary
As Contributors:  Takeshi Morita 
Preprint link:  scipost_202010_00029v1 
Date submitted:  20201031 09:31 
Submitted by:  Morita, Takeshi 
Submitted to:  SciPost Physics Proceedings 
Proceedings issue:  4th International Conference on Holography, String Theory and Discrete Approach in Hanoi 
Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
We propose that Hawking radiationlike phenomena may be observed in systems that show butterfly effects. Suppose that a classical dynamical system has a Lyapunov exponent $\lambda_L$, and is deterministic and nonthermal ($T=0$). We argue that, if we quantize this system, the quantum fluctuations may imitate thermal fluctuations with temperature $T \sim \hbar \lambda_L/2 \pi $ in a semiclassical regime, and it may cause analogous Hawking radiation. We also discuss that our proposal may provide an intuitive explanation of the existence of the bound of chaos proposed by Maldacena, Shenker and Stanford.
Current status:
Submission & Refereeing History
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Reports on this Submission
Anonymous Report 1 on 20201213 (Invited Report)
Strengths
1) the paper is well written and presents its main ideas clearly;
2) the content of the paper is original and its main proposal is wellmotivated via a few pedagogical examples;
3) the paper helps to better understand the origin of the socalled bound on chaos, which is important in the context of black holes physics, manybody quantum chaos, condensed matter theory, etc.
Weaknesses
1) In my opinion, the paper is already very good, but it could be even better if the author provides a more detailed comparison with previous results in the literature. In particular, I think the paper would greatly benefit from a more detailed comparison with the results of reference [9], by J. Kurchan.
Report
In the paper "Analogous Hawking Radiation in Butterfly Effect", Takeshi Morita proposes that in nonthermal systems that show sensitive dependence on initial conditions, quantum mechanics effects lead to the appearance of an effective temperature.
The author argues that the bound on chaos, $\lambda_L \leq \frac{2 \pi T}{\hbar}$, might be seen as a lower bound to the system's temperature: $T \geq \frac{\hbar \lambda_L}{2 \pi}$. In particular, the effective temperature introduced by quantum effects, $T_\text{eff} \sim \frac{\hbar \lambda_L}{2 \pi}$, defines a thermal scale below which quantum fluctuations overcome the thermal ones, and the thermal equilibrium may be disturbed. This provides a nice way to understand the chaos bound proposed by Maldacena, Shenker, and Stanford.
In my opinion, the paper is well written and presents original content. Therefore, I recommend the paper for publication after one minor clarification has been addressed.
Requested changes
1)
I think the paper would greatly benefit if the author includes a more detailed comparison with previous results in the literature, in particular with reference [9], by J. Kurchan.
In [9], J. Kurchan explains the bound on chaos in a simple way. He defines a Lyapunov length scale, $\ell_0$, and argues that the bound on chaos appears when $\ell_0$ is comparable to the de Broglie length scale $\ell_\text{dB}$. Since, $\ell_0 \sim T^{1/2}$ and $\ell_\text{dB} \sim T^{1/2}$, J. Kurchan's results seem to be consistent with the results obtained by Takeshi Morita, because for very low temperatures the de Broglie length scale becomes bigger than the Lyapunov length scale. I think the author could add a paragraph comparing his results with the ones in reference [9].
Author: Takeshi Morita on 20201216
(in reply to Report 1 on 20201213)Dear Referee,
I would like to thank the referee for reading my manuscript and giving valuable comments. As the referee pointed out, my result is consistent with Ref.[9]. I added footnote 8 about this interesting relation to Ref.[9] at the end of section 3.2.
Sincerely,
Takeshi Morita