Skip to main content

Questions tagged [non-equilibrium]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
4 votes
0 answers
64 views

Does Equipartition hold in overdamped dynamics?

We start with the Langevin equation $$m\frac{\mathrm{d}^{2}x}{\mathrm{d}t^{2}} = -\Gamma \frac{\mathrm{d}x}{\mathrm{d}t} +\sqrt{2\Gamma k_{B}T} \eta(t). $$ Now, we know that at $t \gg m/\Gamma$, the ...
6 votes
0 answers
60 views

Relation between time-ordered propagator in condensed matter and Feynman propagator

In particle physics I am used to the Feynman propagator being decomposed into positive and negative frequency Wightman functions. For example, this is the representation used in Eq. (6.2.13) of ...
1 vote
1 answer
215 views

Reference request for semiclassical approximations for Schwinger-Keldysh path integrals

Can some one provide some resources for understanding semi-classical approximations for Schwinger-Keldysh path integrals. Is there any discussion about instanton (and multi-instanton) (for even single ...
0 votes
0 answers
21 views

Pressure difference between a box and the outside atmosphere

Say I have a box of volume $V$, with an ideal gas inside it with temperature $T_b$. I don't know the number of particles inside it. The box is surrounded by the room's environment, which has ...
1 vote
0 answers
39 views

Evaluating the PDF of an active Ornstein-Uhlenbeck process

I am going through this paper: Inertial Self-Propelled Particles. For a free-particle, when there is no external potential, the authors have written the stochastic differential equations as - $$\dot{\...
2 votes
0 answers
35 views

Relation between Dyson equation, Kadanoff-Baym equations and 2PI formalism

I am learning the framework of non-equilibrium field theory. Probably this is clear enough to an expert, but the expansive number of formalism, methods, and frameworks is confusing for a beginner. I ...
3 votes
1 answer
207 views

Deriving diffusion coefficients from Newtonian mechanics of Lennard-Jones phases?

The diffusion coefficient is known in the traditional physical literature as an empirical parameter of Fick's law. Here the observation is that spatial gradients of densities are suppressed by a rate ...
0 votes
0 answers
23 views

Average drift time across a membrane

In my statistical mechanics course, we were given the following method to find the average drift time across a membrane of thickness $d$ with a potential difference of $V$ across it. Solving the ...
1 vote
0 answers
19 views

Floquet Theory and Quantum Quench

Floquet Theory and Quantum Quench are approaches to study systems far from equilibrium (e.g. periodic driving of a closed system). Floquet Theory helps to find a unitary operator $Q(t)$ such that it ...
0 votes
0 answers
10 views

Linewidth from correlation functions

I work on cavity modes interacting with matter inside the cavity and I want to determine the linewidth of the light. I do not have excess to the state of the system directly but in a steady state, I ...
2 votes
0 answers
25 views

Integration by parts to switch sign on anti-Hermitian Louivillian

I am self studying non-equilibrium stat mech and a common theme is that I am unable to reproduce the "this follow from integration by parts" parts of derivations. Here is the most recent: In ...
0 votes
1 answer
60 views

Callen's Statistical and Thermo approach

In the Callen's paper pointed out two approaches for evolution of systems out of equilibrium. In one part he says The statistical approach consists of generalizing the methods of statistical ...
2 votes
2 answers
928 views

Understanding how entropy works [closed]

I need to have a fully functioning understanding of entropy so I've got a few questions to ask What are the conditions for an increase in entropy to be reversible? I (think) I know that any process ...
-8 votes
3 answers
210 views

How Taylor series is compatible with special relativity?

In mathematics, an analytic function is defined by its possession of a Taylor series with a positive radius of convergence ($R_c​>0$). Notably, certain analytic functions—such as holomorphic ...
4 votes
0 answers
193 views

How much entanglement does each quasiparticle carry?

The dynamics of entanglement entropy $S$ out of equilibrium can be understood in some regimes from the point of view of the quasiparticle picture: an excited state acts as a source of pairs of ...
2 votes
2 answers
356 views

What rigid body rotation causes rotational viscosity?

According to the book Non-Equilibrium Thermodynamics by S. R. De Groot and P. Mazur page 309, there are some rigid body rotations causing rotational viscosity. What kind of fluid is that? How can this ...
0 votes
0 answers
26 views

The Relation btw Clausius' and Boltzmann's Statements of the 2nd Law during a State Change within a Finite Time Interval

In his book, Non-Equilibrium Thermodynamics and Statistical Mechanics, Attard takes an approach to deduce a relationship between the probability of state (Boltzmann's statement of the 2nd Law) and the ...
11 votes
4 answers
3k views

Diffusion coefficient for asymmetric (biased) random walk

I want to obtain a Fokker-Planck like equation by taking the continuous limit of a discrete asymmetric random walk. Let the probability of taking a step to the right be $p$, and the probability of ...
0 votes
0 answers
29 views

A general approach to choosing/deriving response functions?

I'm interested in applying some simple linear response theory to a (weakly) non-equilibrium system. For example, consider a microscopic rigid body attached to a wall at a certain point, and that this ...
1 vote
0 answers
50 views

Self-energy of a spinon coupled to a $\rm U(1)$ gauge field

I would like to understand how to calculate the 1-loop self-energy for spinons coupled to a $\rm U(1)$ gauge field. For context, I am going through Nagaosa & Lee's "Gauge theory of the normal ...
0 votes
0 answers
17 views

Whether there is an isolated system, it will enter equilibrium [duplicate]

For a thermodynamically isolated system, will it eventually move toward thermal equilibrium? Will there be exceptions to the system?
7 votes
3 answers
861 views

Is entropy maximum in equilibrium?

Usually, in the context of non-equilibrium thermodynamics, it is said that entropy achieves a maximum in equilibrium, so the Taylor series expansion of entropy around the equilibrium state as a ...
1 vote
0 answers
28 views

Observables expressed by the lesser Green's function $\tilde{\mathcal{G}}^{<}(k, E)$

I am reading the paper PRB 106, 035102 (2022). In the supplementary materials, it says, within the Green’s function formalism, the thermal and quantum average of an observable θ is expressed as, $$\...
0 votes
0 answers
35 views

Partition function in Non-equilibrium field theory in statistical mechanics

Consider a system that described by the Hamiltonian $H(t)$, contains non-adiabatic time-dependent external fields and the evolution drives the system away from equilibrium. Now the partition function ...
0 votes
0 answers
31 views

Keldysh contour and time-dependent observables

How to use the non-equilibrium Keldysh Green's function to solve a driven harmonic oscillator? A quantum harmonic oscillator $H_0 = \omega_0 a^\dagger a $ is coupled to a pump field E(t) (refer to ...
2 votes
1 answer
55 views

Meaning of Gibbs average

This might sound a very amateur question but I couldn't find the answer anywhere. Simply, what is the meaning of Gibbs average? I've came across this term on the paper: Transmission of Information ...
1 vote
0 answers
69 views

What are the differences between stationary and nonstationary black holes?

I am a bit confused about what are the properties that hold for black holes in general and which ones only hold for stationary black holes. Let me try to explain what I know and hopefully people can ...
1 vote
1 answer
68 views

Entropy for non-equilibrium processes

How can one derive a general expression for the entropy production in a system undergoing a non-equilibrium process, such as a non-equilibrium phase transition or a stochastic fluctuation?
0 votes
0 answers
26 views

How do you determine the Pull Direction for a GROMACS umbrella sampling simulation to generate the most accurate free energy value?

I am trying to calculate the free energy between a protein and aptamer using GROMACS. Literature has indicated that one of the best way to do so is by performing an umbrella sampling MD simulation ...
1 vote
0 answers
32 views

Detailed derivations about Mode Coupling Theory (MCT)

I am currently reading two articles related to mode coupling theory (MCT) and I am stuck in evaluating some ensemble averages, since there is no detailed derivations given. Moreover, the two ...
-1 votes
1 answer
53 views

What is an good book to study classical non-equilibrum thermodynamics? [duplicate]

I am a physics student who has just started my master's program and am taking a course on classical non-equilibrium thermodynamics. I am looking for a book that can help me learn this subject. Are ...
23 votes
6 answers
4k views

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 ...
1 vote
0 answers
52 views

Application of Schwinger-Keldysh formalism in various topics except cosmology

I want to find some theories or models on Schwinger-Keldysh formalism (in-in formalism) focusing on flat spacetime in terms of correlation functions. For example, I know there are many applications ...
8 votes
1 answer
355 views

How to perform stroboscopic measurements for Floquet topological insulators?

Floquet topological insulators (arXiv:1008.1792, arXiv:1211.5623) have attracted much research interests in condensed matter physics. The goal is to realize topological insulators from trivial ...
0 votes
1 answer
26 views

Is it possible for a droplet to condense in the middle (bulk rather than boundary) of the vapor without impurity?

As a rule of thumb, vapor condensation usually happens at the interface between the system and the heat reservoir. Now, according to my analysis below, it is the only way for vapor to condense, which ...
3 votes
1 answer
97 views

A question on relaxation time approximation

I was learned that the form of collision term in relaxation time approximation is set to be: $$\left (\frac{\partial f}{\partial t}\right)_c=-\frac{f-f^0}{\tau}$$ in with $f^0$ is local equilibrium ...
3 votes
1 answer
106 views

A problem in solving a PDE of the time-ordered Green function

In the article written by Jauho in 2006 Introduction to the Keldysh nonequilibrium Green function technique, I've tried to operating with whether $g_{k\alpha}^t$ or $g_{k\alpha}^{-1}$ from right to ...
1 vote
1 answer
1k views

Boltzmann equation: how to estimate the relaxation time?

A widespread approximation of the full integro-differential Boltzmann equation is the so-called "relaxation time approximation", where the collisional integral is replaced by: $$ \partial_t ...
16 votes
1 answer
2k views

Relation between Langevin and Fokker-Planck for exponentially correlated noise

What is the corresponding Fokker-Planck equation for, $\frac{df(t)}{dt}=-kf(t)+\zeta(t)$ where, $\zeta(t)$ is random noise? In particular, how will the Fokker-Planck equation look if $\zeta(t)$ is ...
0 votes
0 answers
30 views

Spontaneous emission as dissipation and fluctuation

Suppose we have some sort of medium and we want to build an effective theory of light inside. Of course we want to calculation the dielectric constant, which in turn is determined by the ...
3 votes
1 answer
273 views

Issue deriving Fokker-Planck equation starting from Boltzmann's equation

I was trying to derive the Fokker-Planck equation starting from the Boltzmann's equation and I run into some issue while trying to do so. Starting from Boltzmann and using the notation $f \equiv f(x, ...
9 votes
5 answers
1k views

Sufficient and necessary conditions on random walk to obtain standard diffusion equation

In the simplest random walk model that is generally considered, the probability of the finding the particle at time $t$ in $x$, $P(x,t)$ is given by, $$ P(x,t) = \frac{1}{2}\big[ P(x-a, t-\tau) + P(x+...
2 votes
0 answers
40 views

If a system lies in a non-equilibrium state initially, and there are two possible equilibrium final states. How does the system evolve? [closed]

This should be the area of non-equilibrium thermodynamics. The system is in a non-equilibrium state and after a long time it will evolve into an equilibrium state. But now we have two possible final ...
1 vote
0 answers
40 views

Can the Keldysh occupation function have a zero for bosons or a pole for fermions?

In the Keldysh framework for nonequilibrium dynamics of quantum systems we learn that there are essentially two Green's functions that characterize a system: the retarded Green's function $G^R(\omega)$...
1 vote
2 answers
174 views

Electrostatics of non-equilibrium situations

In footnote 1 of Chapter 13 of Ashcroft and Mermin, they remark that The only case we shall discuss in which the local equilibrium distribution is not the uniform equilibrium distribution (13.1) (...
1 vote
0 answers
27 views

Distinguishing between equilibrium and non-equilibrium distributions?

Suppose a physical system is described by some effective double-well potential landscape with fluctuation-driven motion along this landscape. If we watch the system for a sufficiently long time and ...
1 vote
0 answers
63 views

Boltzmann equation for Lennard-Jones particles?

In the Vlasov variant of Boltzmann equation, the Coulomb pair forces are included via the force term that appears as the prefactor of the derivative of the density with respect to velocity. In that ...
0 votes
0 answers
70 views

From Newtonian mechanics to Boltzmann (or statistical) mechanics

Classical mechanical systems observable on a dynamical scale are subject to Newton's laws. In this case, knowledge of the Hamiltonian allows us to minimize energy taking into account inertia. This ...
2 votes
0 answers
175 views

What is the relation between Kubo's formula and the Green-Kubo relations?

In one hand, Kubo's formula is used in linear response quantum mechanics to obtain response functions (conductivity, magnetic susceptibility, dielectric function) and so on in terms of correlation ...
0 votes
0 answers
23 views

Exact form of two-time correlators in out of equilibrium evolution from factorized distributions

Suppose that the have an initial product state at some time $t=0$ written in a computational basis $|0\rangle,|1\rangle$, for instance the state $|1011010\rangle$. The associated density matrix $\...

1
2 3 4 5
7