167 research outputs found
A brief introduction to the scaling limits and effective equations in kinetic theory
These lecture notes provide the material for a short introductory course on
effective equations for classical particle systems. They concern the basic
equations in kinetic theory, written by Boltzmann and Landau, describing
rarefied gases and weakly interacting plasmas respectively. These equations can
be derived formally, under suitable scaling limits, taking classical particle
systems as a starting point. A rigorous proof of this limiting procedure is
difficult and still largely open. We discuss some mathematical problems arising
in this context.Comment: arXiv admin note: substantial text overlap with arXiv:1611.0708
Mean-field limit and Semiclassical Expansion of a Quantum Particle System
We consider a quantum system constituted by identical particles
interacting by means of a mean-field Hamiltonian. It is well known that, in the
limit , the one-particle state obeys to the Hartree equation.
Moreover, propagation of chaos holds. In this paper, we take care of the
dependence by considering the semiclassical expansion of the
-particle system. We prove that each term of the expansion agrees, in the
limit , with the corresponding one associated with the Hartree
equation. We work in the classical phase space by using the Wigner formalism,
which seems to be the most appropriate for the present problem.Comment: 44 pages, no figure
Propagation of Chaos and Effective Equations in Kinetic Theory: a Brief Survey
We review some historical highlights leading to the modern perspective on the
concept of chaos from the point of view of the kinetic theory. We focus in
particular on the role played by the propagation of chaos in the mathematical
derivation of effective equations
The Boltzmann-Grad Limit of a Hard Sphere System: Analysis of the Correlation Error
We present a quantitative analysis of the Boltzmann-Grad (low-density) limit
of a hard sphere system. We introduce and study a set of functions (correlation
errors) measuring the deviations in time from the statistical independence of
particles (propagation of chaos). In the context of the BBGKY hierarchy, a
correlation error of order measures the event where particles are
connected by a chain of interactions preventing the factorization. We show
that, provided , such an error flows to zero with
the average density , for short times, as , for some positive . This provides an information
on the size of chaos, namely, different particles behave as dictated by the
Boltzmann equation even when diverges as a negative power of .
The result requires a rearrangement of Lanford perturbative series into a
cumulant type expansion, and an analysis of many-recollision events.Comment: 98 pages, 12 figures. Subject of the Harold Grad Lecture at the 29th
International Symposium on Rarefied Gas Dynamics (Xi'an, China). This revised
version contains new results (a theorem on the convergence of high order
fluctuations; estimates of integrated correlation error) and several
improvements of presentation, inspired by comments of the anonymous refere
On the evolution of the empirical measure for the Hard-Sphere dynamics
We prove that the evolution of marginals associated to the empirical measure
of a finite system of hard spheres is driven by the BBGKY hierarchical
expansion. The usual hierarchy of equations for measures is obtained as a
corollary. We discuss the ambiguities arising in the corresponding notion of
microscopic series solution to the Boltzmann-Enskog equation
On the validity of the Boltzmann equation for short range potentials
We consider a classical system of point particles interacting by means of a
short range potential. We prove that, in the low--density (Boltzmann--Grad)
limit, the system behaves, for short times, as predicted by the associated
Boltzmann equation. This is a revisitation and an extension of the thesis of
King (unpublished), appeared after the well known result of Lanford for hard
spheres, and of a recent paper by Gallagher et al (arXiv: 1208.5753v1). Our
analysis applies to any stable and smooth potential. In the case of repulsive
potentials (with no attractive parts), we estimate explicitly the rate of
convergence
A diffusion limit for a test particle in a random distribution of scatterers
We consider a point particle moving in a random distribution of obstacles
described by a potential barrier. We show that, in a weak-coupling regime,
under a diffusion limit suggested by the potential itself, the probability
distribution of the particle converges to the solution of the heat equation.
The diffusion coefficient is given by the Green-Kubo formula associated to the
generator of the diffusion process dictated by the linear Landau equation
Derivation of the Fick's Law for the Lorentz Model in a low density regime
We consider the Lorentz model in a slab with two mass reservoirs at the
boundaries. We show that, in a low density regime, there exists a unique
stationary solution for the microscopic dynamics which converges to the
stationary solution of the heat equation, namely to the linear profile of the
density. In the same regime the macroscopic current in the stationary state is
given by the Fick's law, with the diffusion coefficient determined by the
Green-Kubo formula.Comment: 33 pages, 7 figure
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