An alternative to Plemelj-Smithies formulas on infinite determinants

An alternative to Plemelj - Smithies formulas for the p -regularized quantities $d^{(p)}(K)$ and $D^{(p)}(K)$ is presented which generalizes previous expressions with $p=1$ due to Grothendieck and Fredholm. It is also presented global upper bounds for these quantities. In particular we prove that |d^{(p)}(K)| \le e^{\kappa \n K \n_p^p} holds with $\kappa = \kappa(p) \le \kappa(\infty) = \exp \bigl\{-{1 \over 4(1+ e^{2 \pi})} \bigr\}$ for $p\ge 3$ which improves previous estimate yielding $\kappa(p) = e (2 + \ln(p-1))$.Comment: CYCLER Paper 93Jan00

On the Mayer series of two-dimensional Yukawa gas at inverse temperature in the interval of collapse

A Theorem on the minimal specific energy for a system with \pm 1 charged particles interacting through the Yukawa pair potential v is proved which may stated as follows. Let v be represented by scale mixtures of d-dimensional Euclid's hat (cutoff at short scale distances) with d\geq 2. For any even number of particles n, the interacting energy U_{n} divided by n, attains an n-independent minimum at a configuration with zero net charge and particle positions collapsed altogether to a point. For any odd number of particles n, the ratio U_{n}/(n-1) attains its minimum value, the same of the previous cases, at the configuration with \pm 1 net charge and particle positions collapsed to a point. This Theorem is then used to resolve an obstructive remark of an unpublished paper (Remark 7.5 of \cite{Guidi-Marchetti}) which, whether the standard decomposition of the Yukawa potential into scales were adopted, would impede a direct proof of the convergence of the Mayer series of the two-dimensional Yukawa gas for the inverse temperature in the whole interval [4\pi ,8\pi ) of collapse. In the present paper, it is proven convergence up to the second threshold 6\pi and its given explanations on the mechanism that allow it to be extend up to 8\pi . The paper distinguishes the matters concerning stability from those related to convergence of the Mayer series. In respect to the latter the paper dedicates to the Cauchy majorante method applied to the density function of Yukawa gas in the interval of collapses. It also dedicates to the proof of the main Theorem and estimates of the modified Bessel functions of second kind involved in both representations of two-dimensional Yukawa potential: standard and scale mixture of the Euclid's hat function.Comment: 49 pages, 7 figure

The Falicov-Kimball Model with Long--Range Hopping Matrices

The ground state nature of the Falicov-Kimball model with unconstrained hopping of electrons is investigated. We solve the eigenvalue problem in a pedagogical manner and give a complete account of the ground state energy both as a function of the number of electrons and nuclei and as a function of the total number of particles for any value of interaction U. We also study the energy gap and show the existence of a phase transition characterized by the absence of gap at the half--filled band for U<0. The model in consideration was proposed and solved by Farkasovsky for finite lattices and repulsive on-site interaction U>0. Contrary to his proposal we conveniently scale the hopping matrix to guarantee the existence of the thermodynamic limit. We also solve this model with bipartite unconstrained hopping matrices in order to compare with the Kennedy--Lieb variational analysis.Comment: 23 pages, Late

On the Virial Series for a Gas of Particles with Uniformly Repulsive Pairwise Interaction

The pressure of a gas of particles with a uniformly repulsive pair interaction in a finite container is shown to satisfy (exactly as a formal object) a "viscous" Hamilton-Jacobi (H-J) equation whose solution in power series is recursively given by the variation of constants formula. We investigate the solution of the H-J and of its Legendre transform equation by the Cauchy-Majorant method and provide a lower bound to the radius of convergence on the virial series of the gas which goes beyond the threshold established by Lagrange's inversion formula. A comparison between the behavior of the Mayer and virial coefficients for different regimes of repulsion intensity is also provided.Comment: Preliminary version; 62 pages, 9 figure

Rakib-Sivashinsky and Michelson-Sivashinsky Equations for Upward Propagating Flames: A Comparison Analysis

We establish a comparison between Rakib--Sivashinsky and Michelson-Sivashinsky quasilinear parabolic differential equations governing the weak thermal limit of upward flame front propagating in a channel. For the former equation, we give a complete description of all steady solutions and present their local and global stability analysis. For the latter, multi-coalescent unstable steady solutions are introduced and shown to be exponentially more numerous than the previous known coalescente solutions. This fact is argued to be responsible for the disagreement of the observed dynamics in numerical experiments with the exact (linear) stability analysis and also gives the ingredients to describe the quasi-stable behavior of parabolic steadily propagating flame with centered tip.Comment: 17 pages, 3 figure

Renormalization Group Flow of the Two-Dimensional Hierarchical Coulomb Gas

We consider a quasilinear parabolic differential equation associated with the renormalization group transformation of the two-dimensional hierarchical Coulomb system in the limit as the size of the block L goes to 1. We show that the initial value problem is well defined in a suitable function space and the solution converges, as t goes to infinity, to one of the countably infinite equilibrium solutions. The nontrivial equilibrium solution bifurcates from the trivial one. These solutions are fully described and we provide a complete analysis of their local and global stability for all values of inverse temperature. Gallavotti and Nicolo's conjecture on infinite sequence of ``phases transitions'' is also addressed. Our results rule out an intermediate phase between the plasma and the Kosterlitz-Thouless phases, at least in the hierarchical model we consider.Comment: 34pages,2figures, to appear in CM

Hierarchical Spherical Model as a Viscosity Limit of Corresponding O(N)Heisenberg Model

The O(N) Heisenberg and spherical models with interaction given by the long range hierarchical Laplacean are investigated. Two classical results are adapted. The Kac--Thompson solution [KT] of the spherical model, which holds for spacially homogeneous interaction, is firstly extended to hierarchical model whose interaction fails to be translation invariant. Then, the convergence proof of O(N) Heisenberg to the spherical model by Kunz and Zumbach [KZ] is extended to the long range hierarchical interaction. We also examine whether these results can be carried over as the size of the hierarchical block L goes to 1. These extensions are considered a preliminary study prior the investigation of the model by renormalization group given in [MCG] where central limit theorems for the spherical (N=\infty) model on the local potential approximation (L\downarrow 1) are then established from an explicit solution of the associate nonlinear first order partial differential equation

Combinatorial Solution of One-Dimensional Quantum Systems

We give a self-contained exposition of the combinatorial solution of quantum mechanical systems of coupled spins on a one-dimensional lattice. Using Trotter formula, we write the partition function as a generating function of a spanning subgraph of a two-dimensional lattice and solve the combinatorial problem by the method of Pfaffians provided the weights satisfy the so-called free fermion condition. The free energy and the ground state energy as a function of the inverse temperature, couplings J and magnetic fields h, for the XY model in a transverse field with period p=1 and 2, is then obtained.Comment: Number of figures: 9 (eps

Singular perturbation of nonlinear systems with regular singularity

We extend Balser-Kostov method of studying summability properties of a singularly perturbed inhomogeneous linear system with regular singularity at origin to nonlinear systems of the form \varepsilon zf^{\prime} = F(\varepsilon,z,f) with F a \mathbb{C}^{\nu}-valued function, holomorphic in a polydisc \bar{D}_{\rho}\times \bar{D}_{\rho}\times \bar{D}_{\rho}^{\nu}. We show that its unique formal solution in power series of \varepsilon, whose coefficients are holomorphic functions of z, is 1-summable under a Siegal-type condition on the eigenvalues of F_{f}(0,0,0). The estimates employed resemble the ones used in KAM theorem. A simple Lemma is developed to tame convolutions that appears in the power series expansion of nonlinear equations.Comment: 18 page

Conformal Deformation from Normal to Hermitian Random Matrix Ensembles

We investigate the eigenvalues statistics of ensembles of normal random matrices when their order N tends to infinite. In the model the eigenvalues have uniform density within a region determined by a simple analytic polynomial curve. We study the conformal deformations of normal random ensembles to Hermitian random ensembles and give sufficient conditions for the latter to be a Wigner ensemble.Comment: 23 page