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F. Bagarello

Publications and source records attributed to F. Bagarello.

At least 55 records · Page 3Linked to original sources
arXiv2009

An operatorial approach to stock markets

We propose and discuss some toy models of stock markets using the same operatorial approach adopted in quantum mechanics. Our models are suggested by the discrete nature of the number of shares and of the cash which are exchanged in a real market, and by the existence of conserved quantities, like the total number of shares or some linear combination of cash and shares. The same framework as the one used in the description of a gas of interacting bosons is adopted.

q-fin.GN↗
arXiv2009

Gabor-like systems in $L^2({\bf R}^d)$ and extensions to wavelets

In this paper we show how to construct a certain class of orthonormal bases in $L^2({\bf R}^d)$ starting from one or more Gabor orthonormal bases in $L^2({\bf R})$. Each such basis can be obtained acting on a single function $Ψ(\underline x)\in L^2({\bf R}^d)$ with a set of unitary operators which operate as translation and modulation operators {\em in suitable variables}. The same procedure is also extended to frames and wavelets. Many examples are discussed.

math-ph↗
arXiv2009

Multiplication of Distributions in one dimension: possible approaches and applications to $δ$-function and its derivatives

We introduce a new class of multiplications of distributions in one dimension merging together two different regularizations of distributions. Some of the features of these multiplications are discussed in a certain detail. We use our theory to study a certain number of examples, involving products between Dirac delta functions and its successive derivatives.

math-ph↗
arXiv2009

Multiplication of distributions in any dimension: applications to $δ$-function and its derivatives

In two previous papers the author introduced a multiplication of distributions in one dimension and he proved that two one-dimensional Dirac delta functions and their derivatives can be multiplied, at least under certain conditions. Here, mainly motivated by some engineering applications in the analysis of the structures, we propose a different definition of multiplication of distributions which can be easily extended to any spatial dimension. In particular we prove that with this new definition delta functions and their derivatives can still be multiplied.

math-ph↗
arXiv2009

Relations between the Hepp-Lieb and the Alli-Sewell laser models

In this paper we show that the dissipative version of the laser model proposed by Alli and Sewell can be obtained by considering the stochastic limit of the (open system) hamiltonian introduced by Hepp and Lieb in their seminal work. We also prove that the Dicke-Haken-Lax hamiltonian produces, after the stochastic limit is considered, the generator of a semigroup with equations of motion very similar to those of Alli-Sewell, and coinciding with these under suitable conditions.

math-ph↗
arXiv2009

Extended SUSY quantum mechanics, intertwining operators and coherent states

We propose an extension of {\em supersymmetric quantum mechanics} which produces a family of isospectral hamiltonians. Our procedure slightly extends the idea of intertwining operators. Several examples of the construction are given. Further, we show how to build up vector coherent states of the Gazeau-Klauder type associated to our hamiltonians.

math-ph↗
arXiv2009

New Structures in the Theory of the Laser Model

In a recent article, Alli and Sewell formulated a new version of the Dicke-Hepp-Lieb laser model in terms of quantum dynamical semigroups, and thereby extended the macroscopic picture of the model. In the present article, we complement that picture with a corresponding microscopic one, which carries the following new results. (a) The local microscopic dynamics of the model is piloted by the classical, macroscopic field, generated by the collective action of its components; (b) the global state of the system carries no correlations between its constituent atoms after transient effects have died out; and (c) in the latter situation, the state of the system at any time $t$ maximises its entropy density, subject to the constraints imposed by the instantaneous values of its macroscopic variables.

math-ph↗
arXiv2009

Many-body applications of the stochastic limit: a review

We review some applications of the perturbative technique known as the {\em stochastic limit approach} to the analysis of the following many-body problems: the fractional quantum Hall effect, the relations between the Hepp-Lieb and the Alli-Sewell models (as possible models of interaction between matter and radiation), and the open BCS model of low temperature superconductivity.

math-ph↗
arXiv2009

Relations between multi-resolution analysis and quantum mechanics

We discuss a procedure to construct multi-resolution analyses (MRA) of $\Lc^2(\R)$ starting from a given {\em seed} function $h(s)$ which should satisfy some conditions. Our method, originally related to the quantum mechanical hamiltonian of the fractional quantum Hall effect (FQHE), is shown to be model independent. The role of a canonical map between certain canonically conjugate operators is discussed. This clarifies our previous procedure and makes much easier most of the original formulas, producing a convenient framework to produce examples of MRA.

math-ph↗
arXiv2009

Intertwining operators between different Hilbert spaces: connection with frames

In this paper we generalize a strategy recently proposed by the author concerning intertwining operators. In particular we discuss the possibility of extending our previous results in such a way to construct (almost) isospectral self-adjoint operators living in different Hilbert spaces. Many examples are discussed in details. Many of them arise from the theory of frames in Hilbert spaces, others from the so-called g-frames.

math-ph↗
arXiv2009

The stochastic limit in the analysis of the open BCS model

In this paper we show how the perturbative procedure known as {\em stochastic limit} may be useful in the analysis of the Open BCS model discussed by Buffet and Martin as a spin system interacting with a fermionic reservoir. In particular we show how the same values of the critical temperature and of the order parameters can be found with a significantly simpler approach.

math-ph↗
arXiv2009

Vector coherent states and intertwining operators

In this paper we discuss a general strategy to construct vector coherent states of the Gazeau-Klauder type and we use them to built up examples of isospectral hamiltonians. For that we use a general strategy recently proposed by the author and which extends well known facts on intertwining operators. We also discuss the possibility of constructing non-isospectral hamiltonians with related eigenstates.

math-ph↗
arXiv2009

Derivations of quasi *-algebras

The spatiality of derivations of quasi *-algebras is investigated by means of representation theory. Moreover, in view of physical applications, the spatiality of the limit of a family of spatial derivations is considered.

math-ph↗
arXiv2009

Quasi *-algebras of measurable operators

Non-commutative $L^p$-spaces are shown to constitute examples of a class of Banach quasi *-algebras called CQ*-algebras. For $p\geq 2$ they are also proved to possess a {\em sufficient} family of bounded positive sesquilinear forms satisfying certain invariance properties. CQ *-algebras of measurable operators over a finite von Neumann algebra are also constructed and it is proven that any abstract CQ*-algebra $(\X,\Ao)$ possessing a sufficient family of bounded positive tracial sesquilinear forms can be represented as a CQ*-algebra of this type.

math-ph↗
arXiv2009

A note on faithful traces on a von Neumann algebra

In this short note we give some techniques for constructing, starting from a {\it sufficient} family $\mc F$ of semifinite or finite traces on a von Neumann algebra $\M$, a new trace which is faithful.

math-ph↗