D. Davesne

Publications (9)0 Total impact

• Source

  Available from: ArXiv

  Article: Numerical solution of the Boltzmann equation for the collective modes of trapped Fermi gases

  T. Lepers, D. Davesne, S. Chiacchiera, M. Urban
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  ABSTRACT: We numerically solve the Boltzmann equation for trapped fermions in the normal phase using the test-particle method. After discussing a couple of tests in order to estimate the reliability of the method, we apply it to the description of collective modes in a spherical harmonic trap. The numerical results are compared with those obtained previously by taking moments of the Boltzmann equation. We find that the general shape of the response function is very similar in both methods, but the relaxation time obtained from the simulation is significantly longer than that predicted by the method of moments. It is shown that the result of the method of moments can be corrected by including fourth-order moments in addition to the usual second-order ones and that this method agrees very well with our numerical simulations. Comment: 13 pages, 8 figures, accepted for publication in Phys. Rev. A
  04/2010;
• Source

  Available from: ArXiv

  Article: Collective modes of trapped Fermi gases with in-medium interaction

  S. Chiacchiera, T. Lepers, M. Urban, D. Davesne
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  ABSTRACT: Due to Pauli blocking of intermediate states, the scattering matrix (or $T$ matrix) of two fermionic atoms in a Fermi gas becomes different from that of two atoms in free space. This effect becomes particularly important near a Feshbach resonance, where the interaction in free space is very strong but becomes effectively suppressed in the medium. We calculate the in-medium $T$ matrix in ladder approximation and study its effects on the properties of collective modes of a trapped gas in the normal-fluid phase. We introduce the in-medium interaction on both sides of the Boltzmann equation, namely in the calculation of the mean field and in the calculation of the collision rate. This allows us to explain the observed upward shift of the frequency of the quadrupole mode in the collisionless regime. By including the mean field, we also improve considerably the agreement with the measured temperature dependence of frequency and damping rate of the scissors mode, whereas the use of the in-medium cross section deteriorates the description, in agreement with previous work.
  01/2009;
• Source

  Available from: arxiv.org

  Article: Two-pion production processes, chiral symmetry and NN interaction in the medium

  G. Chanfray, D. Davesne, M Ericson, M. Martini
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  ABSTRACT: We study the two-pion propagator in the nuclear medium. This quantity appears in the $\pi-\pi$ T-matrix and we show that it also enters the QCD scalar susceptibility. The medium effects on this propagator are due to the influence of the individual nucleon response to a scalar field through their pion clouds. This response is appreciably increased by the nuclear environment. It produces an important convergence effect between the scalar and pseudoscalar susceptibilities, reflecting the reshaping of the scalar strengh observed in $2\pi$ production experiments. While a large modification of the $\sigma$ propagator follows, due to its coupling to two pion states, we show that the NN potential remains instead unaffected. Comment: 14 pages, 4 figures, submitted to EPJ A
  06/2004;
• Source

  Available from: arxiv.org

  Article: Random Phase Approximation and Extensions Applied to a Bosonic Field Theory

  H. Hansen, G. Chanfray, D. Davesne, P. Schuck
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  ABSTRACT: An application of a self-consistent version of RPA to quantum field theory with broken symmetry is presented. Although our approach can be applied to any bosonic field theory, we specifically study the $\phi^4$ theory in 1+1 dimensions. We show that standard RPA approach leads to an instability which can be removed when going to a superior version,i.e. the renormalized RPA. We present a method based on the so-called charging formula of the many electron problem to calculate the correlation energy and the RPA effective potential.
  03/2002;
• Source

  Available from: arxiv.org

  Article: In-medium Pion-Pion Interaction and Chiral Symmetry Restoration

  D. Davesne, Y. J. Zhang, G. Chanfray, J. Wambach
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  ABSTRACT: We discuss medium modifications of the unitarized pion-pion interaction in the nuclear medium. We incorporate both the effects of chiral symmetry restoration and the influence of collective nuclear pionic modes, originating from the p-wave coupling of the pion to delta-hole configurations. We show how the resulting strong enhancement of the sigma-meson spectral function is related to large fluctuations of the condensate associated with the partial restoration of chiral symmetry.
  03/2000;
• Source

  Available from: archives-ouvertes.fr

  Article: Pion Scalar Density and Chiral Symmetry Restoration at Finite Temperature and Density

  G. Chanfray, D. Davesne, J. Delorme, M Ericson, J. Marteau
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  ABSTRACT: This paper is devoted to the evaluation of the pionic scalar density at finite temperature and baryonic density. We express the latter effect in terms of the nuclear response evaluated in the random phase approxima- tion. We discuss the density and temperature evolution of the pionic density which governs the quark condensate evolution. Numerical evalua- tions are performed.
  01/2000;
• Source

  Available from: arxiv.org

  Article: Medium Modification of The Pion-Pion Interaction at Finite Density

  D. Davesne, Y. J. Zhang, G. Chanfray
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  ABSTRACT: We discuss medium modifications of the unitarized pion-pion interaction in the nuclear medium. We incorporate both the effects of chiral symmetry restoration and the influence of collective nuclear pionic modes originating from the p-wave coupling of the pion to delta-hole configurations. We show in particular that the dropping of the sigma meson mass significantly enhances the low energy structure created by the in-medium collective pionic modes. Comment: 26 pages, 7 figures included, Latex file
  09/1999;
• Article: Pion dispersion relation in hot pion matter

  G. Chanfray, D. Davesne
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  ABSTRACT: We study the modification of the pion propagation properties when it is embedded in hot pionic matter. We calculate the real part and the imaginary part of the pion self-energy in a scheme, analogous to the Brckner-Hartree-Fock approximation used in nuclear physics, which allows to incorporate in a fully consistent way unitarity and Bose correlations at finite temperature. We discuss the consequences of the medium effects on the pion transverse momentum spectrum measured in ultrarelativistic heavy ion collisions and the so-called soft pion puzzle.
  Zeitschrift für Physik A Hadrons and Nuclei 02/1994; 349(1):65-76.
• Source

  Available from: arxiv.org

  Article: How to preserve symmetries with cut-off regularized integrals?

  T. Varin, D. Davesne, M. Oertel, M. Urban
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  ABSTRACT: We present a prescription to define quadratically and logarithmically divergent parts of several integrals employing a cut-off in agreement with some symmetry requirements. As examples we consider one-loop Ward identities for QED and a phenomenological chiral model.
  Nuclear Physics A.