Questions tagged [non-equilibrium]

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Probability density during equilibration

An ensemble of states $x$ are initially drawn from a non-equilibrium probability density $P_0(x)$. Over time they will evolve towards the equilibrium distribution $P_\mathrm{eq}(x)$. What I want to ...
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0answers
25 views

Is there a classical correspondence of the entanglement entropy in isolated quantum systems?

For an isolated quantum system, one can study the time evolution of entanglement entropy after a quantum quench (always a pure state), which has a rich behaviour in various different models. However, ...
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1answer
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How did Carnevale et al. could argue mass in a ballistically aggregating systetm evolves as $t^{2d/(d+2)}$?

I am trying to understand this paper but I am not able to do it. Please help. See the paper here. First of all how could they write collision time $t_0$ as given there?. I am not able to get it even ...
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25 views

What is the BKT transition in non-equilibrium systems?

There is a useful page on the BKT (or KT) transition here which describes the role of vortices in 2d equilibrium systems. I am interested in what happens in 2d non-equilibrium driven-dissipative ...
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26 views

Example of two-dimensional Langevin equation?

I am looking for an example of a langevin-equation with two variables: $\dot{x}=f(x,t)+\omega, x=(x_1,x_2)$. Can anyone suggest one?
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5answers
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Is thermodynamics only applicable to systems in equilibrium?

So I was going through callen's thermodynamics book and their he says that thermodynamics is only applicable to systems which are in equilibrium and that naturally raised a few questions in my mind ...
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1answer
39 views

Accurate derivation of electron-phonon scattering contribution to metal resistivity

My lecture derived the expression for this contribtuin using the collision integral approach but I missed lot of details. He considers the lowest order correction to distribution function $f=f_0+\...
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64 views

Fluctuation-Dissipation Theorem in the Keldysh Formalism

In Kamenev's book Field Theory of Non-Equilibrium Systems (he also has lecture notes online here, which contains the relevant statement on pg. 17), he states that the following equation $$G^K(\epsilon)...
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31 views

Derivation of Feynman rules from generating functional for non-eq QFT

I consider Yukawa non-equilibrium theory with interaction $g\bar{\psi}\phi\psi$ with massive fermionic field $\psi$ with mass $m$ and massive scalar field $\phi$ with mass $M$. I would like to ...
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38 views

Non-eq QFT: functional formalism

I am looking for references (papers, books etc.) where I can find pedagogical introduction to non-eq QFT without hamiltonian approach. I mean that an author start from writing down the generating ...
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49 views

Question about the Markovian property of the velocity of a Brownian particle following Langevin equation

I'am now studying Langevin model and Fokker-Planck equation with the lecture notes by Borghini Topics in Nonequilibrium Physics (NB: PDF). On page 92, he talks about the Markovian property of the ...
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40 views

Landau Theory of fluctuations

With respect to chapter 12 in the book Statistical Physics(Part 1) by Landau and Lifshitz, I am currently stuck at the intepretation of Fluctuation theory that Landau provides. In the neighbourhood of ...
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1answer
35 views

How is heat dissipation rate the product of force and velocity?

Let $q$ be heat dissipation to midium, $F$ be the force to a particle, and $\dot{x}$ is the velocity of it. According to the equation (8) in Seifert 2005, $\dot{q} = F \dot{x}$ holds. How does this ...
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1answer
69 views

Entropy production, local thermodynamic equilibrium and adiabatic process

It is said that for local thermodynamic equilibrium the local entropy production needs to be 0. Now, I am reading the following from the book by de Groot and Mazur "Non-Equilibrium Thermodynamics". ...
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1answer
46 views

Equilibrium and non-equilibrium thermodynamic states?

I have the following two states. I have classified them as equilibrium and non-equilibrium and I am not sure if that is the right category my problem is I need to understand what parameters to look ...
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18 views

Thermalization and structure formation, starting with a pure state coupled to heat bath

I am looking for tractable quantum mechanical systems which show thermalisation and/or structure formation. One idea is a small quantum system S, e.g. a quantum Heisenberg model in a pure state (the ...
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1answer
42 views

Can spontaneous fluctuations cause instantaneous non-equilibrium?

The fluctuation-dissipation theorem says that the linear response of a given system to an external perturbation is expressed as the fluctuation properties of the system in thermal equilibrium. Does ...
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1answer
68 views

Does the First law of thermodynamics hold if the final state is NOT in equilibrium?

So we know the first low of thermodynamics holds for isolated systems $$\Delta E = W+Q\tag{1}$$ Now assuming we are in a thermally isolated system such that $(Q=0)$ we obtain $$\Delta E= W\tag{2}$$...
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What is the intuition behind the statement that non-equilibrium systems with static disorder are self-averaging?

In this paper(1) by C. De Dominics, he makes the argument that in a dynamical statistical mechanics system, one doesn't need to apply the replica trick and can directly disorder average the generating ...
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62 views

Detailed Balance Violation and Fokker-Planck Equation

Suppose I have a system with N sites, and each site can be modified (M) or anti-modified (A). Transitions between these two states are in part random, and in part auto-regulated by recruitment of At ...
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0answers
258 views

Exact solution for non-linear Fokker-Planck equation

I'm searching for exact (analytical) results for FP equation in 2 variables (such as $x$ and $p$ in 1D) with a steady state. Kramer's like (with force due to confining potential, such as harmonic ...
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1answer
165 views

Heat transfer between a common material and a non-thermalizable one?

I've read that some systems cannot reach equilibrium (page 15 of the book Selected Scientific Papers of Sir Rudolf Peierls: With Commentary or R. Peierls, “Zur kinetischen Theorie der Wärmeleitung in ...
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33 views

Why the distribution of Fluctuationg force in brownian motion has gaussian distribution?

I am reading the Zwanzig's book and I have a confusion about the average of the fluctuating force and its distribution. As it says $F(t)$ is a random variable that means it has a probability ...
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0answers
52 views

Statistical physics at very large particle number

According to this manuscript http://www.math.lmu.de/~michel/credits/Federica_Pezzotti_phd.pdf it is proposed (e.g. at page 18) that particle correlations between particles can be neglected in the ...
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27 views

Why are the electrodes in thermodynamic equilibrium for a working solar cell?

I was reading a paper that performed simulation of a solar cell under illuminated conditions. Obviously, in these conditions, the device is out of thermodynamic equilibrium. For example the ...
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0answers
31 views

Is there a multiscale analysis for field theories?

Consider a (zero dimensional) Gaussian field theory described by the dynamical action $$S = \int_t \tilde{\phi}(t) \left[\partial_t \phi(t) + M(t) \phi(t)\right] - \gamma \tilde{\phi}(t)^2\, .$$ $\...
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1answer
171 views

What is the difference between non-equilibrium and equilibrium phase transitions?

My question is about the distinction between certain kinds of phase transitions. I understand what the difference between first and second order ones are. What is the difference between non ...
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1answer
57 views

Why does the Boltzmann equation deal with single-particle phase space density?

Why does the Boltzmann equation deal with single-particle phase space density $\rho_{1}(\textbf{r}_1,\textbf{p}_1,t)$ rather than the N-particle phase space density $\rho(\{\textbf{r}_i,\textbf{p}_i,t\...
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2answers
87 views

Book(s) fills the gap from introductory thermo to nonequilibrium thermo/stat mech for self-taught student?

I know this is a big question. But as a graduate student, my research is somehow related to nonequilibrium thermodynamics/statistical mechanics. TBH, I hate how some research treat this subject like a ...
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1answer
99 views

Do electrons really diffuse when a temperature gradient is applied?

In many websites and books, it is generally said that the charge carriers, be it electrons or holes, diffuse through the considered material when a temperature gradient is applied. However I have ...
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0answers
79 views

How to numerically calculate Fisher zeros?

The main quantity in the study of dynamical quantum phase transition (DQPT) is Loschmidt echo amplitude defined as $G(t)=\langle \Psi_{0}|\Psi_{0}(t)\rangle=\langle \Psi_{0}|e^{-iHt}|\Psi_{0}\rangle$...
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1answer
49 views

Work performed by ramping of magnetic field (non-interacting Ising model) [closed]

Consider the following hamiltonian $$H=-h\sum_{i=1}^N\sigma_i$$ where $\sigma_i=\pm1$ and $h$ is the magnetization. Let us assume that the system is equilibrated with a bath at temperature $T$ with ...
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1answer
122 views

Does Irreversibly/no detailed balance implies there is no thermal equilibrium?

Consider the following transition matrix $$ T= \left[ {\begin{array}{cccc} \frac{1}{3} & \frac{1}{4} & \frac{1}{5} & \frac{1}{6}\\ \frac{1}{3} & \frac{1}{4} & \frac{1}{...
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1answer
48 views

free stress boundary condition

I would like to understand better the free stress boundary condition. Indeed, force equilibrium writes $\nabla.\sigma=0$, and not $\sigma=0$, so which basic physical principle (such as force ...
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0answers
46 views

Closed form of Iterated integrals arising in Fredholm's integral equation solution in the context of Nonequilibrium Quantum field Theory?

While solving a Non-equilibrium quantum field theory problem I came across this class of $2n_{}^{\text{th}}$ order iterated integral : $$F(T_{}^{},T_{0}^{},\epsilon)=\int_{T_{0}^{}}^{T_{}^{}}dt_{1}^{}...
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0answers
39 views

What sense is there in entropy arguments when the system can't be known to be ergodic?

What sense does "entropy" make in non-equilibrium dynamics? What is its definition? How is the "entropy of the early universe" calculated, for example? And how can the "entropy of the universe" be ...
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0answers
38 views

Generalized reaction rate for elementary process

Most textbooks give the reaction rate $$r = k [\mathrm{R}_1]^{a_1}[\mathrm{R}_2]^{a_2} \tag{1}$$ for the elementary process $a_1 \mathrm{R}_1 + a_2 \mathrm{R}_2 \rightarrow \mathrm{P}$. However, ...
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1answer
67 views

How is 'nonlinear optics' related to 'nonequilibrium'?

According to what I found, nonlinear optical process is related to nonequilibrium physics - nonequilibrium green's function (Keldysh green's function/formalism) appears in nonlinear optics. However, ...
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1answer
28 views

Formation of patterns in instabilities according to the wavelength of instability

Do the wavelengths of the instability have an influence on the type of patterns that we are going to get? Meaning for example in 2D, if the unstable wavelengths are small with respect to the size of ...
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0answers
78 views

Derivation of the Keldysh-Non-Linear-Sigma model

I have to give a presentation on the Keldysh Non Linear Sigma model in a proseminar at my university. I am new to the topic and I have had some problems with understanding the literature. My main ...
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0answers
25 views

Why is a quantum quench considered as a quantum analog of a thermodynamic transformation?

In the paper of A. Silva, he mentioned that it is possible to characterize a quantum quench, from the perspective of nonequilibrium physics, using work statistics because the quantum quench is ...
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54 views

What is meant by “phase space structure”?

I've heard that non-equilibrium systems have the property that their phase space has a structure, as opposed to 'structure-less' phases spaces of equilibrium systems. What does this precisely mean? I'...
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1answer
70 views

Kramers Equation and Ito vs Stratonovich

In the derivation of the (Klein)-Kramers equation it is possible to start from the differential equations: $$\frac{d\vec v(t)}{dt}=\vec F(\vec r)-\zeta(\vec r) \vec v(t)+\sqrt{2\zeta(\vec r)k_B T(\vec ...
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1answer
18 views

Rotational diffusion - why isn't $\hat n(t)=\hat n(0) \; \forall t$?

Consider the rotational Langevin equation in the absence of an external force: $$\frac{d \hat n(t)}{dt} =\vec{\xi}(t) \times \hat n(t)$$ where $\vec \xi(t)$ is a Gaussian white noise and $\hat n(t) \...
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1answer
152 views

Fluctuations in Fluctuation Dissipation theorem

In the derivation of the Fluctuation-Dissipation theorem. We encounter an identity $$ \langle\delta A(t) \delta B(0) \rangle = \langle A(t)B(0)\rangle-\langle A \rangle\langle B\rangle$$ where $$\...
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147 views

What is the relation between eigenstate thermalisation and infinite heating in Floquet systems?

Closed quantum systems with periodically changing parameters (Floquet systems) typically heat up to an infinite temperature at large times. I have read multiple times (the last time was here) that ...
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34 views

Logistic Growth: Mean Field Equation

I was told a while ago that for the logistics growth process: $$x \underset{k_2}{\stackrel{k_1}{\rightleftharpoons}}x+x$$the mean field equation for the population $n$ is given by: $$\frac{d\bar n}{dt}...
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1answer
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Why is it interesting to study “quantum quench” at a critical point?

In the presentation, "Quantum Quenches in Extended Systems", by S. Sotiriadis, P. Calabrese and J. Cardy, it was pointed out that quatum quench through a critical point remains an open problem. Why ...
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1answer
568 views

How to pass for Langevin equation to Fokker-Planck equation?

What is the procedure to pass from the description of a phenomenon made by the Langevin equation: $$ \frac{dv}{dt}=-\frac{v}{\tau}+\sqrt{2c}\,\eta $$ to the corresponding description with the Fokker-...
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1answer
51 views

Why is matter wave field usually assumed to be be intrinsically stable?

In the paper "Collapse and revival of the matter wave field of a Bose-Einstein condensate" by M. Greiner, O. Mandel, T. Haensch and I. Bloch, it was stated that Bose-Einstein condensate (BEC) ...