5,712 research outputs found
An Efficient Method for the Solution of Schwinger--Dyson equations for propagators
Efficient computation methods are devised for the perturbative solution of
Schwinger--Dyson equations for propagators. We show how a simple computation
allows to obtain the dominant contribution in the sum of many parts of previous
computations. This allows for an easy study of the asymptotic behavior of the
perturbative series. In the cases of the four-dimensional supersymmetric
Wess--Zumino model and the complex scalar field, the singularities
of the Borel transform for both positive and negative values of the parameter
are obtained and compared.Comment: 9 pages, no figures. Match of the published version, with the
corrections in proo
Lectures on the three--dimensional non--commutative spheres
These are expanded notes for a short course given at the Universidad Nacional
de La Plata. They aim at giving a self-contained account of the results of
Alain Connes and Michel Dubois--Violette.Comment: 17 page
Approximate Differential Equations for Renormalization Group Functions in Models Free of Vertex Divergencies
I introduce an approximation scheme that allows to deduce differential
equations for the renormalization group -function from a
Schwinger--Dyson equation for the propagator. This approximation is proven to
give the dominant asymptotic behavior of the perturbative solution. In the
supersymmetric Wess--Zumino model and a scalar model which do not
have divergent vertex functions, this simple Schwinger--Dyson equation for the
propagator captures the main quantum corrections.Comment: Clarification of the presentation of results. Equations and results
unchanged. Match the published version. 12 page
Alien Calculus and non perturbative effects in Quantum Field Theory
In many domains of physics, methods are needed to deal with non-perturbative
aspects. I want here to argue that a good approach is to work on the Borel
transforms of the quantities of interest, the singularities of which give
non-perturbative contributions. These singularities in many cases can be
largely determined by using the alien calculus developed by Jean \'Ecalle. My
main example will be the two point function of a massless theory given as a
solution of a renormalization group equation.Comment: 4 pages, double-colum
The Standard Model of Leptons as a Purely Vectorial Theory
We propose a way to reconcile the Standard Model of leptons with a purely
vectorial theory. The observed neutrino is predicted to be massless. The
unobservability of its partner and the structure of the weak currents are
given the same origin.Comment: 10 pages. Latex, 8 postscript figures included. We have corrected 2
(cancelling) sign misprints, and made explicit that we also recover the usual
couplings of the U(1) gauge field B. The conclusions are unchanged. PAR-LPTHE
93/1
Integrable mappings and polynomial growth
We describe birational representations of discrete groups generated by
involutions, having their origin in the theory of exactly solvable
vertex-models in lattice statistical mechanics. These involutions correspond
respectively to two kinds of transformations on matrices: the
inversion of the matrix and an (involutive) permutation of the
entries of the matrix. We concentrate on the case where these permutations are
elementary transpositions of two entries. In this case the birational
transformations fall into six different classes. For each class we analyze the
factorization properties of the iteration of these transformations. These
factorization properties enable to define some canonical homogeneous
polynomials associated with these factorization properties. Some mappings yield
a polynomial growth of the complexity of the iterations. For three classes the
successive iterates, for , actually lie on elliptic curves. This analysis
also provides examples of integrable mappings in arbitrary dimension, even
infinite. Moreover, for two classes, the homogeneous polynomials are shown to
satisfy non trivial non-linear recurrences. The relations between
factorizations of the iterations, the existence of recurrences on one or
several variables, as well as the integrability of the mappings are analyzed.Comment: 45 page
Conventionalisation? Organic farming bites back!
This is a summary of the discussion during the workshop 2.6 on conventionalisation of organic farming and how farmers or farmers' associations avoid conventionalisation. It also includes the abstracts of the papers that were presented during the workshop
The quantum Neumann model: asymptotic analysis
We use semi--classical and perturbation methods to establish the quantum
theory of the Neumann model, and explain the features observed in previous
numerical computations.Comment: 14 pages, 3 figure
The quantum Neumann model: refined semiclassical results
We extend the semiclassical study of the Neumann model down to the deep
quantum regime. A detailed study of connection formulae at the turning points
allows to get good matching with the exact results for the whole range of
parameters.Comment: 10 pages, 5 figures Minor edit
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