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Publications FYMA
Recherchez une publication dans la base de données FYMA en
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32 publications trouvées pour ' 1998'
UCL-IPT-98-20
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Partial *-algebras: A retrospective
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Références:
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(Proc. 12th Max Born Symposium, Wroclaw, September 1998), B. Jancewicz and W. Karwowski (eds.); Lecture Notes in Physics, vol. 539, pp. 161-179, Springer-Verlag, Berlin, (2000)
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Résumé:
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We review the main points in the development of pa s during the last 15 years, at three different levels. (i) The algebraic structure stemming from the partial multiplication; (ii) The topological pa s; (iii) The pa s of closable operators in Hilbert spaces or po s, including the representation theory of the abstract pa s.
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UCL-IPT-98-19 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, I. Mahara
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Titre:
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Galilean wavelets: Coherent states of the affine Galilei group
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Références:
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Journal of Mathematical Physics 40 (1999) pp. 5956-5971
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Résumé:
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We derive Galilean wavelets, by which we mean coherent states of the affine Galilei group, that is, the Galilei group extended by independent space and time dilations. The construction follows a general method based on square integrable group representations, possibly modulo a subgroup, i.e., on a homogeneous space of the underlying group. We also examine the restriction to the Schrödinger subgroup, which contains only dilations that leave invariant the Schrödinger and the heat equations.
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UCL-IPT-98-17
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Auteurs:
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A. Coron, P. Flandrin, N. Gache
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Titre:
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Modulated Fractional Gaussian Noise: A Process With Non-Gaussian
wavelet details
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Références:
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IEEE SP International Symposium on Time-Frequency and Time-Scale Analysis TFTS-98, Pittsburgh, pp. 361-364
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Résumé:
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The aim of this communication is to propose a very simple model that is able to reproduce both scaling laws and scale dependent non-Gaussian wavelet details. It is based on the modulated version of a fractional Gaussian noise. Its power spectrum and the probability density functions of its discrete wavelet details are investigated and illustrated. Some examples based on simulated and real data are also given.
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UCL-IPT-98-16 : ( ps.gz)
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Auteurs:
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R. Lefevere
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Titre:
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Weakly Gibbsian Measures and Quasilocality: a long range pair-interaction counterexample
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Références:
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J. Stat. Phys. 95 (1999) 785-789
preprint mp_arc 98-701
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Résumé:
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We exhibit an example of a measure on a discrete and finite spin system whose conditional probabilities are given in terms of an almost everywhere absolutely summable potential but are discontinuous almost everywhere.
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UCL-IPT-98-15 : ( ps.gz)
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Auteurs:
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R. Lefevere
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Titre:
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Variational Principle for Some Renormalized Measures
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Références:
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J. Stat. Phys. 96 (1999) 109-134
preprint mp_arc 98-613
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Résumé:
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We show that some measures suffering from the so-called
Renormalization Group pathologies satisfy a variational principle
and that the corrresponding limit of the pressure, with boundary
conditions in a set of measure 1, is proportional to the pressure
of the Ising model.
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UCL-IPT-98-14 : ( ps.gz)
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Auteurs:
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Jean Bricmont, K. Gawedzki, A. Kupiainen
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Titre:
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KAM Theorem and Quantum Field Theory
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Références:
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Communications in Mathematical Physics 201 (1999) 699-727
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Résumé:
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We give a new proof of the KAM theorem for analytic Hamiltonians. The proof is inspired by a quantum field theory formulation of the problem and is based on a renormalization group argument treating the small denominators inductively scale by scale. The crucial cancellations of resonances are shown to follow from the Ward identities expressing the translation invariance of the corresponding field theory.
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UCL-IPT-98-13 : ( ps.gz)
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Auteurs:
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D. Altschüler, Philippe Ruelle, E. Thiran
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Titre:
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On parity functions in conformal field theories
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Références:
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J. Phys. A: Math. Gen. 32 (1999) 3555-3570
hep-th/9808158
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Résumé:
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We examine general aspects of parity functions arising in rational conformal field theories, as a result of Galois theoretic properties of modular transformations. We focus more specifically on parity functions associated with affine Lie algebras, for which we give two efficient formulas. We investigate the consequences of these for the modular invariance problem.
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UCL-IPT-98-12 : ( ps.gz)
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Auteurs:
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C. Smith
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Titre:
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SU(N) Elastic Rescattering in B and D
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Références:
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Résumé:
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UCL-IPT-98-10 : ( ps.gz)
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Auteurs:
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G.C. Branco, D. Delepine, D. Emmanuel-Costa, R. Gonzalez
Felipe
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Titre:
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Electroweak Baryogenesis in the Presence of an Isosinglet Quark
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Références:
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Phys. Lett. B442 (1998) pp. 229-237
hep-ph/9805302
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Résumé:
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We consider the possibility of electroweak baryogenesis in a simple extension of the standard model with an extra singlet complex scalar and a vector-like down quark. We show that in the present model the first-order electroweak phase transition can be strong enough to avoid the baryon asymmetry washout by sphalerons and that the $CP$-violating effects can sufficient to explain the observed baryon-to-entropy ratio $n_{B}/s \sim 10^{-10}$. Other appealing features of the model include the generation of a CKM phase from spontaneous $CP$ breaking at a high energy scale and a possible solution of the strong $CP$ problem through the natural suppression of the parameter $\bar \theta$.
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UCL-IPT-98-09 : ( ps.gz)
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Auteurs:
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G. Lopez Castro, Jean Pestieau
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Titre:
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Arithmetic and the standard electroweak theory
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Références:
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hep-ph/9804272
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Résumé:
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We propose the relations $1/e - e = 3$ and tan$2\theta_W$ = 3/2, where $e$ is the positron charge and $\theta_W$ is the weak angle. Present experimental data support these relations to a very high accuracy. We suggest that some duality relates the weak isospin and hypercharge gauge groups of the standard electroweak theory.
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UCL-IPT-98-08 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, P. Vandergheynst
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Titre:
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Wavelets on the 2-sphere and related manifolds
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Références:
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Proc. Workshop on geometrical methods in physics (Bialowiecza, July 1997) - Reports on Mathematical Physics 43 (1999) pp. 13-24
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Résumé:
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We present a group theoretical derivation of the continuous wavelet transform (CWT) on the 2-sphere, based on the construction of coherent states associated to square integrable group representations. The parameter space X is the product of SO(3) X R^+_*, embedded into the Lorentz group SO(3,1) via the Iwasawa decomposition, and X = SO(3,1)/C. The space L^2(S^2) carries a unitary irreducible representation of SO(3,1) which is square integrable over X, and thus yields the wavelets on S^2 and the associated CWT.
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UCL-IPT-98-06 : ( ps.gz)
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Auteurs:
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G. Thonet, O. Blanc, P. Vandergheynst, E. Pruvot, J.-M. Vesin, Jean-Pierre Antoine
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Titre:
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Wavelet-based detection of ventricular ectopic beats in heart rate signals
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Références:
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Applied Signal Processing 5 (1998) pp. 170-181
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Résumé:
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The purpose of this work is to present a wavelet-based method for the detection of a particular set of perturbations of the heart rhythm called ventricular ectopic beats or extrasystoles. Directly identifying these sudden changes in heart rate signals is determinant for clinical prognosis since several previous studies have shown that extrasystoles are potential factors in the triggering of ventricular tachyarrhythmias. The proposed method is a three-step procedure: time-warping based preprocessing, detection using maxima of the wavelet transform, and final selection of relevant patterns. Different examples of application to heart rate signals retrieved from implanted cardioverter-defibrillators are presented.
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UCL-IPT-98-05
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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The Continuous Wavelet Transform in image processing
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Références:
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CWI Quraterly 11 (1998), pp. 1-23
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Résumé:
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We begin with a short review of the 2-D continuous wavelet transform (CWT), covering successively the mathematical properties, the various analyzing wavelets and the calibration problem. Then, after a short outline of the discrete wavelet transform , we present a fast algorithm for the CWT. Then we discuss the group-theoretica background of the CWT, which allows a straightforward extension to more general situations. We conclude with some physical applications.
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UCL-IPT-98-04 : ( ps.gz)
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Auteurs:
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Jean-Marc Gérard, Jean Pestieau, Jacques Weyers
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Titre:
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Hadronic Phases and Isospin Amplitudes in $D(B) \to \pi \pi$ and $D(B) \to K \bar K$ Decays
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Références:
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Phys. Lett. B 436 (1998) pp. 363-368
hep-ph/9803328
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Résumé:
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Hadronic phases in $\pi \pi$ and $K \bar K$ channels are calculated \`a la Regge. At the $D$ mass one finds $\delta_{\pi\pi} \simeq {\pi \over 3}$ and $\delta_{K \bar K} \simeq -
{\pi \over 6}$ in good agreement with the CLEO data while at the $B$ mass these angles are predicted to be, respectively, 11$^\circ$ and -7$^\circ$. With the hadronic phase $e^{i\delta_{K\bar K}}$ taken into account, a quark diagram decomposition of the isospin invariant amplitudes in $D \to K \bar K$ decays fits the data provided the exchange diagram contribution is about $1/3$ of the tree level one.
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UCL-IPT-98-03 : ( ps.gz)
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Auteurs:
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Philippe Ruelle, O. Verhoeven
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Titre:
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Discrete symmetries of unitary minimal conformal theories
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Références:
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Nucl. Phys. B535 (1998) 650-680
hep-th/9803129
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Résumé:
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We classify the possible discrete (finite) symmetries of two-dimensional critical models described by unitary minimal conformally invariant theories. We find that all but six models have the group Z2 as maximal symmetry. Among the six exceptional theories, four have no symmetry at all, while the other two are the familiar critical and tricritical 3-Potts models, which both have an S3 symmetry. These symmetries are the expected ones, and coincide with the automorphism groups of the Dynkin diagrams of simply-laced simple Lie algebras ADE. We note that extended chiral algebras, when present, are almost never preserved in the frustrated sectors.
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UCL-IPT-98-02 : ( ps.gz)
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Auteurs:
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D. Delepine
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Titre:
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A Model for a Dynamically Induced Large $CP$-Violating Phase
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Références:
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Talk given at the 7th workshop on particles and fields (21-27 November 1997, Morelia Mich., Mexico)
hep-ph/9802349
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Résumé:
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Assuming a new interaction with a $\theta$ term for the third generation of quarks, a value of $\theta$ different from zero dynamically induces the top-bottom mass splitting and a large $CP$-violating phase.
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UCL-IPT-98-01 : ( ps.gz)
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Auteurs:
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D. Delepine, Jean-Marc Gerard, Jean Pestieau, Jacques Weyers
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Titre:
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Final state interaction phases in $(B \to K \pi)$ decay amplitudes
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Références:
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Phys. Lett. B 429 (1998) pp. 106-110
hep-ph/9802361
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Résumé:
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A simple Regge pole model for $K\pi$ scattering explains the large phase $e^{i\delta}$ between isospin amplitudes which is observed at the $D$ meson mass $(\delta \approx {\pi\over 2})$. It predicts $\delta \approx 14^\circ - 20^\circ$ at the $B$ mass. Implications for $(B \to K\pi)$ decays and extensions of the model to other two-body decay channels are briefly discussed.
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UCL-IPT-97-24 : ( pdf| pdf)
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Auteurs:
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Radelet Patricia
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Titre:
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La moindre action comme lien entre la philosophie naturelle et la mécanique analytique : continuités d'un questionnement
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Références:
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LLULL, Revista de la Sociedad Espanola de Historia de la Ciensas y las Tecnicas, 21 (1998) 439-484
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Résumé:
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UCL-IPT-97-23 : ( pdf)
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Auteurs:
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Radelet Patricia
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Titre:
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La diatribe du Docteur Akakia, médecin du Pape
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Références:
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Séminaire ``Interférences' du Centre Interfacultaire d'Etude en Histoire des Sciences, Louvain-la-Neuve
Revue des Questions Scientifiques 169 (1998) 209-250
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Résumé:
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UCL-IPT-97-22 : ( pdf)
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Auteurs:
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Radelet-de Grave, Patricia
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Titre:
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Articles : Euler et Bernoulli
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Références:
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Dictionnaire du patrimoine littéraire européen, Patrimoine Littéraire Européen, vol. 10, De Boeck Université, Louvain-la-Neuve (1998) pp. 1-7 et 8-15
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Résumé:
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UCL-IPT-97-21 : ( pdf)
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Auteurs:
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Radelet Patricia
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Titre:
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A glance at Biot's work and at its historical context.
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Références:
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Bulletin de la Classe des Sciences de l'Académie royale de Belgique 7-12 (1998) pp. 237-256
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Résumé:
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UCL-IPT-97-19 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, P. Vandergheynst
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Titre:
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Wavelets on the n-sphere and other manifolds
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Références:
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Journal of Mathematical Physics 39 (1998) pp. 3987-4008
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Résumé:
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We present a purely group-theoretical derivation of the continuous wavelet transform (CWT) on the $(n-1)$-sphere $S^{n-1}$, based on the construction of general coherent states associated to square integrable group representations. The parameter space of the CWT, $Y \sim SO(n)\times BR_*^+$, is embedded into the generalized Lorentz group $SO_o(n,1)$ via the Iwasawa decomposition, so that $X \simeq SO_o(n,1)/N$, where $N \simeq BR^{n-1}$. Then the CWT on $S^{n-1}$ is derived from a suitable unitary representation of $SO_o(n,1)$ acting in the space $L^2(S^{n-1},d\mu)$ of finite energy signals on $S^{n-1}$, which turns out to be square integrable over $X$. We find a necessary condition for the admissibility of a wavelet, in the form of a zero mean condition, which entails all the usual filtering properties of the CWT. Next the Euclidean limit of this CWT on $S^{n-1}$ is obtained by redoing the construction on a sphere of radius $R$ and performing a group contraction for $R\to \infty$, from which one recovers the usual CWT on flat Euclidean space. Finally, we discuss the extension of this construction to the two-sheeted hyperboloid $H^{n-1} \sim SO_o(n-1,1)/SO(n-1)$ and some other Riemannian symmetric spaces.
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UCL-IPT-97-18 : ( pdf)
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Auteurs:
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Radelet Patricia
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Titre:
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Article : Les Bernoulli
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Références:
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Dictionnaire critique de la science classique, Flammarion (1998) 195-205
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Résumé:
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UCL-IPT-97-15 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Quantum mechanics beyond Hilbert space
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Références:
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Quantum Theory in Rigged Hilbert Spaces - Semigroups, Irreversibility and Causality. Lecture Notes in Physics 504 (1998) pp. 3-33; A. Bohm, H.D. Doebner, P. Kielanowski (eds.) Springer-Verlag-Berlin
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Résumé:
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When describing a quantum mechanical system, it is convenient to consider state vectors that do not belong to the hs. In the first part of this paper, we survey the various formalisms have been introduced for giving a rigorous mathematical justification to this procedure: hs s (RHS), scales or lattices of hs s (LHS), nested hs s, partial inner product spaces. Then we present three types of applications in quantum mechanics, all of them involving spaces of analytic functions. First we present a LHS built around the Bargmann space, thus giving a natural frame for the Fock-Bargmann (or phase space) representation. Then we review the RHS approach to scattering theory (resonances, Gamow vectors, etc.). Finally, we reformulate the Weinberg-van Winter integral equation approach to scattering in the LHS language, and this allows us to prove that it is in fact a particular case of the
familiar complex scaling method.
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UCL-IPT-97-14 : ( ps.gz)
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Auteurs:
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Jean-Marc Gérard, G. Lopez Castro
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Titre:
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Tests for the asymptotic behaviour of the $\gamma^\ast \to \gamma \pi^0$ form factor
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Références:
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Phys. Lett. B 425 (1998) pp. 365-368
hep-ph/9709404
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Résumé:
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The $\gamma^\ast \to \omega \pi^0$ transition measured at different photon virtualities already provides us with a clean test for the behaviour of the $\pi^0 \gamma^\ast \gamma$ off-shell axial anomaly at large time-like squared momenta. It also allows reliable predictions for the branching ratio of heavy quarkonium decays into $\omega \pi^0$.
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UCL-IPT-97-13 : ( ps.gz)
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Auteurs:
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R. Gonzalez Felipe
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Titre:
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On the Chern-Simons Topological Term at Finite Temperature
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Références:
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Phys. Lett. B417 (1998) pp. 114-118
hep-th/9709079
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Résumé:
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The parity-violating topological term in the effective action for 2+1 massive fermions is computed at finite temperature in the presence of a constant background field strength tensor. Gauge invariance of the finite-temperature effective action is also discussed.
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UCL-IPT-97-11 : ( ps.gz)
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Auteurs:
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D. Delépine, R. Gonzalez Felipe, Jacques Weyers
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Titre:
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Equivalence of the Sine-Gordon and Massive Thirring Models at Finite Temperature
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Références:
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Phys. Lett. B419 (1998) pp. 296-302
hep-th/9709039
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Résumé:
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Using the path-integral approach, the quantum massive Thirring and sine-Gordon models are proven to be equivalent at finite temperature. This result is an extension of Coleman's proof of the equivalence between both theories at zero temperature. The usual identifications among the parameters of these models also remain valid at $T \neq 0$.
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UCL-IPT-97-09 : ( ps.gz)
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Auteurs:
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M. Beuthe, G. Lopez Castro, Jean Pestieau
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Titre:
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Field theory approach to $K^0 - \bar{K^0}$ and $B^0 - \bar{B^0}$ systems
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Références:
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Int.J.Mod.Phys. A13 (1998) pp. 3587-3600
hep-ph/9707369
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Résumé:
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Quantum field theory provides a consistent framework to deal with unstable particles. We present here an approach based on field theory to describe the production and decay of unstable $K^0 - \bar{K^0}$ and $B^0 - \bar{B^0}$ mixed systems. The formalism is applied to compute the time evolution amplitudes of $K^0$ and $\bar{K^0}$ studied in DAPHNE and CPLEAR experiments. We also introduce a new set of parameters that describe CP violation in $K \to \pi\pi$ decays without recourse to isospin decomposition of the decay amplitudes.
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UCL-IPT-97-05 : ( ps.gz)
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Auteurs:
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Jean Bricmont, A. Kupiainen, R. Lefevere
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Titre:
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Renormalization group pathologies and the definition of Gibbs states
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Références:
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Communications in Mathematical Physics 194 (1998) pp. 359-388
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Résumé:
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We show that the so-called Renormalization Group pathologies in low temperature Ising models are due to the fact that the renormalized Hamiltonian is defined only almost everywhere (with respect to the renormalized Gibbs measures). We construct this renormalized Hamiltonian using a Renormalization Group method developed for random systems and we show that the pathologies are analogous to Griffiths' singularities.
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UCL-IPT-96-19 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine, F. Bagarello, C. Trapani.
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Titre:
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Extension of representations in quasi *-algebras.
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Références:
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Annales de l'Institut H. Poincaré 69 (1998) pp. 241-264
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Résumé:
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Let $(U, U_o)$ be a topological quasi *-algebra, which means in particular that $U_o$ is a topological *-algebra, dense in $U$. Let $\pi^0$ be a *-representation of $U_o$ in some pre-Hilbert space $D \subset \mathcal{H}$ included in H. Then we present several ways of extending $\pi^0$, by closure, to some larger quasi *-algebra contained in $U$, either by Hilbert space operators, or by sesquilinear forms on $D$. Explicit examples are discussed, both abelian and nonabelian, including the CCR algebra.
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UCL-IPT-96-01 : ( ps.gz)
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Auteurs:
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Jean-Pierre Antoine
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Titre:
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Time-dependent wavelets, alias space-time affine coherent states
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Références:
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Quantization, Coherent States, and Poisson Structures (Proc. Bialowieza, July 1995), (1998) pp. 123-132; A. Strasburger, S.T. Ali, J-P. Antoine, J-P. Gazeau, A.Odzijewicz (eds.); Polish Scient. Publ. PWN, Warszawa
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Résumé:
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We describe several families of wavelets associated to the Galilei group, extended by space and time dilations. The construction follows a general method based on group representations which are square integrable only on a homogeneous space of the underlying group.
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UCL-IPT-95-31
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Auteurs:
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Patricia Radelet-de Grave
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Titre:
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Les études de la loi de composition des forces depuis I.H. Westphal (1817) et C. Jacobi (1818) jusqu'à G. Darboux (1875)
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Références:
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Tecnica e Tecnologia nell'architettura dell'ottocento, Atti der quatro seminario di storia delle scienze e delle tecniche (Venezia, 11/11/94)
Pascale Ventrice (Ed.), Publicazione dell'Istituto Veneto di Scienze, Lettere ed Arti, Venezia (1998) pp. 109-151
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Résumé:
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Le 19e siècle voit la naissance du calcul vectoriel dont l'intérêt
n'échappe à aucun ingénieur. Hamilton et Grassmann, les pionniers
reconnus en cette matière commencent tous deux leurs travaux en
1830 et publient, en 1844, l'un ses premiers textes sur les
quaternions et l'autre sa fameuse Ausdehnungslehre. Il n'est donc
pas étonnant d'observer tout au long de ce siècle un intérêt
grandissant pour de nouvelles démonstrations de la loi du
parallélogramme des forces comme pour la comparaison et la
classification des démonstrations existantes. C'est à cet exercice
que se livrent trois auteurs en 1817: J.H. Westphal, C. Jacobi et
Peter Merian puis A.H.C. Westphal, en 1868, et Ernst Goerges, en
1909, au début de notre siècle. Comme le montrent ces travaux,
l'histoire de la démonstration de la loi du parallélogramme
remonte à Aristote et nombreux sont ceux qui en firent la
démonstration. L'article se compose de trois parties. Dans la
première on fait un premier bilan en 1817, à travers les travaux
de trois auteurs: J.H. Westphal, C. Jacobi et P. Merian. La
deuxième partie montre comment les idées é voluent au 19 siè. La
dernière partie, enfin, analyse les axiomes fournis et présentés
comme tels, au cours du 19 siècle par les cinq auteurs qui
analysent les différents types de démonstrations ainsi que par
Araldi, Eytelwein, Poisson, Encontre, Duchayla, Wachter,
Timmermann, Gergonne, Wallace, Dippe, Hearn, Matzka, Darboux et
Schimmack. Tous ces auteurs donnent explicitement les axiomes sur
lesquels reposent leur démonstration.
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