Focaliser sur:  Cacher les contributions
Retour à l'affichage de la conférence
S'authentifier

Critical stability

→ Europe/Paris
Ettore Majorama Centre for Scientific Culture

Ettore Majorama Centre for Scientific Culture

ERICE, Sicily
Aksel Jensen (Physics Department, University of Aarhus), Alejandro Kievsky (INFN and Univ. Pisa), André Martin (CERN-PH, Theory Group), Jean-Marc Richard (Université de Grenoble), Laurent Wiesenfeld (CNRS)
Description
This is the fifth workshop dedicated to the Critical Stability of Few-Body Quantum Systems THE NEXT WORKSHOP WILL BE HELD AT ERICE, OCTOBER 9-15, 2011 SEE http://indico.in2p3.fr/conferenceDisplay.py?confId=4882
Compressed tar file of style files and templates (recommended)
Latex-generated booklet of abstracts
List of participants with affiliation and travel data
Proceedings (alphabetic order)
Proceedings with table of contents
Programme
Template and latex style files for Proceedings (separate files)
Support
  • lundi 13 octobre
    • Welcome; Nuclei I

      Welcome address; first talks on nuclear physics

      • 1
        Welcome address
        This welcome address will briefly present the Ettora Ma jorana Centre for Scientific Culture of Erice, and stress the importance of quantum few-body systems at the edge of stability.
        Orateur: Prof. André Martin (CERN, Geneva, Switzerland)
        pictures
      • 2
        Few-body reactions in nuclear astrophysics
        Stellar nucleosynthesis reactions are responsible for the abundances of the different elements in the Universe. These reactions happen at very low relative energies between the nuclei involved, and the calculation of the corresponding production rates is one of major issues in Nuclear Astrophysics. These reactions can be of different nature (radiative capture, rearrangement processes...) and very often can be described as few-body processes. In this talk we describe how to compute the production rates for three-body radiative capture reactions, using the alpha+n+n --> 6He + gamma process as an example. The calculation includes sequential processes (where an intermediate 5He resonance is populated) as well as direct capture of the two neutrons by the alpha particle. This production rate is compared to the estimated one for the four-body recombination process, alpha+n+n+n --> 6He + n, which compete with the radiative two-neutron capture as a source of 6He. For rearrangement reactions, where the initial nuclei can recombine themselves to produce different final products, we propose the use of the adiabatic approximation as an efficient procedure to distinguish between the different reaction channels, being at the same time possible to compute the transition probabilities at the required very low relative energies.
        Orateur: Prof. Eduardo Garrido (Instituto de Estructura de la Materia, CSIC, Madrid, Spain)
        Slides
      • 3
        Few-Body Approaches and Problems in Hypernuclei
        It takes two nucleons to bind a Lambda hyperon, and perhaps as many as three nucleons to bind two Lambda hyperons. In my talk I will review few-body calculations which are relevant for deciphering the onset of binding in Lambda hypernuclei and in Lambda-Lambda hypernuclei. I will also discuss the onset of binding for Xi hyperons, stabilizing them against the free-space conversion Xi + N --> Lambda + Lambda, which may require a core of two protons, two neutrons and two Lambda hyperons. The Physics implications on the stability of strange hadronic matter will be discussed.
        Orateur: Prof. Avraham Gal (Racah Institute of Physics, Hebrew University, Jerusalem)
        Slides
      • 10:30
        break
      • 4
        The ab initio no-core shell model
        The ab initio no-core shell model (NCSM) is a well-established theoretical framework aimed at an exact description of nuclear structure starting from high precision interactions between the nucleons [1,2]. The principal foundation of the method is the use of effective interactions appropriate for the large, but finite, harmonic-oscillator model spaces employed in the calculations. These effective interactions are derived from the underlying realistic inter-nucleon potentials by a unitary transformation in a way that guarantees convergence to the exact solution as the basis size increases. We will exemplify the performance of the NCSM within nuclear physics by showing recent results from studies of p-shell nuclei. We will also demonstrate the recent adaption of the effective-interaction approach to the many-boson problem [3]. Finally, we will outline an extension of the NCSM formalism to achieve an ab initio description of open quantum systems and nuclear reactions by employing techniques from the Resonating Group Method (RGM) [4]. [1] P. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. Lett. 84 (2000) 5728. [2] P. Navratil, J. P. Vary, and B. R. Barrett, Phys. Rev. C 62 (2000) 054311. [3] J. Christensson, C. Forssén, S. Åberg, and S. M. Reimann, arXiv:0802.2811v1. [4] S. Quaglioni, and P. Navratil, Phys. Rev. Lett. (in press).
        Orateur: Dr Christian Forssén (Chalmers University of Technology)
        Slides
      • 5
        Consistent α-cluster description of the Hoyle state in 12 C
        During the recent years, there is a continuous interest to the experimental and theoretical study of the 12 C nucleus [1, 2, 3, 4]. In this respect, of special importance is the description of the Hoyle state, which was predicted more then 50 years ago merely from the abundance of elements in the universe. Whereas the Hoyle state is fairly well studied experimentally, e. g., its extremely small width Γ and Hoyle to ground-state transition density (in particular, the monopole transition matrix element M12 and the transition radius Atr ) were measured, the theoretical description of a comparable accuracy meets essential difficulties. For the astrophysical applications, the challenging problems is a consistent description of the near-threshold 0+ 2 (Hoyle) state, whose properties are extremely sensitive to parameters in the α-cluster model. On the other hand, the choice of the effective two-body and three-body potentials is of general interest and their parameters have to be adjusted to fit the 12 C observables. Previous calculations [5, 6] revealed that the α-cluster model, even with a simplest local α-α potentials, provides a surprisingly good description of the ground and excited states of the 12 C nucleus. The aim of this reportis to present the calculations of the lowest 0+ states of 12 C with the α-α potentials, which are chosen to describe the s-, d-, g-wave α-α elastic-scattering phase shifts up to energy Ecm < 12 MeV and the experimental energy and width of the α-α resonance (the ground state of 8 Be). The effective three-body potential of a Woods-Saxon form is taken, which parameters are chosen to fix the ground and excited 0+ state energies and the ground-state’s root-mean-square radius at their experimental values. The main result is the amazing descriptive ability of the above-described α-cluster model. The calculations reveal that for a number of the α-α potentials both the width of the Hoyle state Γ and the structural parameters M12 and Atr are in excellent agreement with the experimental data as shown in Fig. 1. There is enough room for further improvement of the model; it is discussed that description of the electromagnetic and (α, α) reactions could be useful to impose additional restrictions on the effective potentials.
        Orateur: Prof. Oleg O. I. Kartavtsev (Dubna, Russia)
        Slides
    • Surface and scattering
      • 6
        The physics of long-range atom-surface interactions and its applications
        he long range interaction between atoms and material surfaces or nanobodies is a case study of a pure quantum system interacting with macroscopic or mesoscopic systems. This field is of increasing importance owing to the fast development of nanoscience and nanotechnologies. The confinement of atoms inside a nano-size space strongly alters the internal properties of the atomic system and its response to external excitation, e.g. light irradiation. In addition to surface-induced energy level shifts and spontaneous emission enhancement/inhibition, there is atom symmetry break due to the anisotropy of the surface near-field, inducing energy level mixing, population transfer, or selective surface-enhancement of forbidden lines… [1] The dramatic influence of surface-guided waves (like morphology-dependent resonances of nanobodies, or surface polariton modes of dispersive materials) on atom-surface van der Waals interactions has also been considered. Experimentally there are two distinct approaches to the investigation of the properties of atoms in interaction with surfaces and nanostructures. High resolution laser spectroscopy at gas-dielectric interfaces (like reflection spectroscopy, or transmission spectroscopy of sub-micrometer vapour cells) allows one to monitor the properties of selected radiative atomic states in a confined environment. Resonant coupling between excited atoms and surface polaritons has led to the first observation of repulsive van der Waals surface forces, as well as the dramatic modification of decay channels and branching ratios of excited states [2]. The influence of thermal surface excitations is now under scrutiny [3]. On the other hand, high resolution momentum spectroscopy with atomic beams gives access to the monitoring of long-lived states interacting with surfaces and nanobodies. Beam-surface diffraction experiment, and transmission of velocity-selected metastable beams trough nano-slits or nano-gratings, has allowed one to study surface-induced symmetry break, and inelastic atom diffraction produced by energy level mixing [4]. Implications in cavity QED, as well as applications to atom optics and interferometry at the nanoscale [5] will be discussed. The conditions of existence of long-range, weakly bound atom-surface complex will be considered. [1] See, e.g., M. Ducloy, in "Nanoscale Science and Technology" (Kluwer, The Netherlands, 1998) 235; V. V. Klimov et al., Kvantovaya Elektronika [Quantum Electronics] 31, 569 (2001); D. Bloch and M. Ducloy, Adv. At. Mol. Opt. Phys., 50, 91 (2005) [2] H. Failache et al., Phys. Rev. Lett. 83, 5467 (1999); ibid. 88, 243603 (2002); Eur. Phys. Journal D23, 237 (2003) [3] M.-P. Gorza et al, Eur. Phys. Journal D, 40, 343 (2006) [4] M. Boustimi et al, Phys. Rev. Lett. 86, 2766 (2001) ; J.-C. Karam et al, Europhys. Letters 74, 36 (2006) [5] J. Grucker et al., Eur. Phys. Journal D, 47, 427 (2008)
        Orateur: Prof. Martial Ducloy (Université Paris 13)
        Slides
      • 7
        Poincar\'e Invariant Three-Body Scattering
        Traditionally three-nucleon calculations are carried out by solving Faddeev equations in a partial wave truncated basis, working either in momentum or in coordinate space. In Ref.~\cite{1} the Faddeev equations were solved directly as function of vector variables for scattering at intermediate energies. The key advantage of this formulation lies in its applicability at higher energies, where special relativity is expected to become relevant. We investigate relativistic three-boson scattering in the framework of Poincar\'{e} invariant quantum mechanics~\cite{wigner}. The main points are the construction of unitary irreducible representations of the Poincar\'{e} group, both for noninteracting and interacting particles. The application to three-body scattering is based on the Faddeev scheme, which is reformulated relativistically. The usage of Poincar\'{e}-Jacobi momenta leads to various algebraic modifications of corresponding standard nonrelativistic expressions. Due to its dependence on the total momentum, the two-body off-shell t-operator entering the Faddeev equation acquires additional momentum dependence beyond the usual energy shift which is characteristic in nonrelativistic calculations. We handle this by using a first resolvent method~\cite{2} and thus can exactly solve for the relativistic two-body operator embedded in the three-body system~\cite{3}. Comparison of the relativistic and non-relativistic calculations lead to observations the should be also relevant for realistic interactions~\cite{4,5}. This comparison does not involve a non-relativistic limit, instead relativistic and non-relativistic three-body calculations with interactions fitted to the same two-body data are compared. All of the differences result from the different ways in which the two-body dynamics appears in the three-body problem. References: {1} H. Liu, Ch. Elster, W. Gl\"ockle, Phys. Rev. C{bf 72}, 054001 (2005). {wigner} E.P. Wigner, Ann. Math. {\bf 40} 149 (1939). {2} B.D. Keister, W.N. Polyzou, Phys. Rev. C{\bf 73}, 014005 (2006). {3} T. Lin, Ch. Elster, W.N. Polyzou, W. Gl\"ockle, Phys. Rev. C{\bf 76} 014010 (2007). {5} T. Lin, Ch. Elster, W.N. Polyzou, H. Witala, W. Gl\"ockle, arXiv:0801.3210 [nucl-th], to appear in Phys. Rev. C.
        Orateur: Prof. Charlotte Elster (Ohio University)
        Slides
      • 8
        Challenges and achievements in the ab-initio three- and four-body scattering calculations: the Coulomb force
        There is a long history of theoretical prescriptions for the solution of the Coulomb problem in three-nucleon continuum. Most of them employ configuration-space framework [1, 2, 3]. In contrast, we solve momentum-space integral equations. The method we use for the inclusion of the Coulomb interaction is based on the ideas proposed in Ref. [4] for two charged particle scattering and extended in Ref. [5] for three-particle scattering, but differs significantly from those earlier works in the practical realization. The Coulomb potential is screened, standard scattering theory for short-range potentials is used, and the renormalization procedure is applied to recover the unscreened limit. In our method [6] the Coulomb potential is screened in a novel way that allows successful application of the numerical techniques developed previously for solving three-nucleon equations without Coulomb and avoids approximations on the nuclear interaction and the treatment of screened Coulomb used in Ref. [5]. The outcome of our method are fully converged calculations for observables of proton-deuteron (pd) elastic scattering and breakup, pd radiative capture, and electromagnetic disintegration of 3 He nuclei; the results for pd elastic scattering agree well with the ones obtained using configuration-space techniques [7]. The method has been extended successfully to four-nucleon scattering [8] and to three-body nuclear reactions [9, 10] involving 4 He, 11 Be or 12 C nuclei. References [1] A. Kievsky, M. Viviani, and S. Rosati, Phys. Rev. C 64, 024002 (2001). [2] C. R. Chen, J. L. Friar, and G. L. Payne, Few-Body Syst. 31, 13 (2001). [3] S. Ishikawa, Few-Body Syst. 32, 229 (2003). [4] J. R. Taylor, Nuovo Cimento B23, 313 (1974); M. D. Semon and J. R. Taylor, ibid. A26, 48 (1975). [5] E. O. Alt et al., Phys. Rev. C 65, 064613 (2002). [6] A. Deltuva, A. C. Fonseca, and P. U. Sauer, Phys. Rev. C 71, 054005 (2005); 72, 054004 (2005). [7] A. Deltuva et al., Phys. Rev. C 71, 064003 (2005). [8] A. Deltuva and A. C. Fonseca, Phys. Rev. Lett. 98, 162502 (2007); Phys. Rev. C 76, 021001(R) (2007). [9] A. Deltuva, Phys. Rev. C 74, 064001 (2006). [10] A. Deltuva et al., Phys. Rev. C 76, 064602 (2007). References [1] G. M. Bruun, A. D. Jackson, and E. E. Kolomeitsev, Phys. Rev. A, 71 052713. [2] P. Massignan, G. M. Bruun, and H. T. C. Stoof, arXiv:0805.3667.
        Orateur: Dr Arnoldas Deltuva (Centro de F ́ısica Nuclear, University of Lisbon, Portugal)
        Slides
      • 16:45
        break
      • 9
        How to model p-scattering using point interactions and related three-body problems
        It is well-known that the celebrated Fermi delta potential model [1,2] leads to non-trivial scattering in the s-channel only. We propose a new family of point interaction models which may be used to describe particles with non-trivial interaction also in the $p$-channel while preserving exact solvability and point character of the interaction [3]. These models are given by self-adjoint operators and their spectral and scattering properies are studied in detail. The developed method is applied to the system of three quantum particles and we discuss the possibillity that this operator is semibounded (in contrast to the Landau Hamiltonian studied by Minlos-Faddeev in the sixties[4]). [1] F.A.Berezin, L.D.Faddeev, Remark on the Schrödinger equation with singular potential. (Russian) Dokl. Akad. Nauk SSSR, 137 (1961), 1011-1014. [2] E. Fermi, Sul moto dei neutroni nelle sostanze idrogenate, Ricerca Scientifica, 7 (1936), 13--52 (In Italian.), English translation in E.Fermi, Collected papers, vol. I, Italy 1921-1938, Univ. of Chicago Press, Chicago, 1962, pp. 980-1016. [3] P. Kurasov, Triplet extensions I: semibounded operators in the scale of Hilbert spaces, accepted for publication in J. d'Analyse Mathématique. [4] R.A. Minlos and L.D. Faddeev, Comment on the problem of three particles with point interactions, Soviet Physics JETP, 14 (1962), 1315-1316.
        Orateur: Dr Pavel Kurasov (Lund University)
        Slides
      • 10
        Feshbach resonances in ultracold atomic gases
        A low energy effective theory based on a microscopic multi-channel description of the atom-atom interaction is derived for the scattering of alkali atoms in different hyperfine states [1]. This theory describes all scattering properties, including medium effects, in terms of the singlet and triplet scattering lengths and the range of the atom-atom potential and provides a link between a microscopic description of Feshbach scattering and more phenomenological approaches based on the treatment of the Feshbach molecule as a point boson. It permits the calculation of medium effects on the resonance coming from the occupation of closed channel states. The examination of such effects are demonstrated to be of particular relevance to an experimentally important Feshbach resonance for 40 K atoms. We then discuss the case of a single impurity interacting resonantly with a gas of fermions and show how it changes from being essentially a quasi-particle excitation to a molecular excitation with increasing coupling strength [2].
        Orateur: Dr Georg Bruun Bruun (Niels Bohr Institute, Copenhagen, Denmark)
        Slides
  • mardi 14 octobre
    • Nuclei-II: Nuclei-II; Coulomb scattering
      • 11
        Four-body nuclear systems
        The study of the four nucleon (4N) system is interesting from a number of different perspectives. First of all, many reactions involving four nucleons, are of extreme astrophysical interest, as they play important roles in solar models or in big-bang nucleosynthesis. Moreover, 4N systems have become increasingly important as testing grounds for models of the nuclear force, being the A=4 system the simplest system that presents the complexity - thresholds and resonances - that characterize nuclear systems. The theoretical description of A=4 systems still constitutes a challenging problem from the standpoint of nuclear few-body theory. Only recently, with the near-constant increase in computing power and the development of new numerical methods, the study of the bound and scattering states has reached a satisfactory level of accuracy. In this contribution, the application of the hyperspherical harmonics method to study these systems will be discussed. The calculations have been performed using realistic models for nucleon-nucleon and three-nucleon forces. The results will be compared with the most recent calculations performed by means of the Faddeev-Yakubovsky approach and the experimental data.
        Orateur: Dr Michele Viviani (INFN, Sezione di Pisa)
        Slides
      • 12
        Three-body force effects in few-nucleon systems
        Orateur: Prof. alejandro kievsky (INFN)
        Slides
      • 13
        Light nuclei in the continuum
        The development of light, neutron-rich beams has opened in the last decade new perspectives for the study of many-neutron systems. Breakup experiments at GANIL will be described, using beams of 6−8 He, 11 Li, 14 Be and 15 B at several tens of MeV/N. Our approach is based on the detection in coincidence of the breakup fragment and the neutrons in order to investigate the different correlations in the final state of these very neutron-rich systems. Several particular cases will be discussed: fragment-n correlations in 7 He, 10 Li and 9 He; 2n correlations in 6 He, 11 Li and 14 Be; and three-body and 4n correlations in 8 He and 14 Be.
        Orateur: Dr Miguel Marqués (LPC, Caen, France)
        Slides
      • 10:45
        break
      • 14
        Solving the Coulomb scattering problem without using coulomb functions
        Few-body systems with the Coulomb interaction are of great interest in atomic and molecular physics. However, solving the Coulomb scattering problem is very difficult from both theoretical and computational points of view because of the long-range nature of the Coulomb potential. The asymptotic boundary conditions at infinity, which are rather complicated for the few-body scattering problem, become even more complicated for the Coulomb problem. Therefore, a method which allows solving the problem without using the asymptotic form of the solution could be an advantage. One of such methods can be constructed with the use of the complex dilation approach. Namely, the total wave function of the system satisfies the homogeneous Schrödinger equation. Subtracting the incoming plane wave from the total solution, we get the driven Schrödinger equation for the function which behaves at infinity as the pure outgoing wave. Applying then the complex scaling method, we reduce the outgoing wave to an exponentially decreasing function. Hence we can use the zero boundary condition at infinity when solving the problem. This approach was shown to be applicable for exponentially decreasing potentials only [1]. If the potential decreases slower, then a divergence occurs. Rescigno et al showed in [2] that the method can be made converging for potentials decreasing faster than the Coulomb one. Namely, one needs to cut off the potential at rather far distance R, and then to apply the exterior complex scaling with the exterior radius R. However, this approach does not work for the Coulomb problem. In the present work, we show how the approach outlined above can be generalized for few-body systems with unscreened Coulomb interactions. We prove this generalization analytically and then show numerically how it works for few systems with long-range interactions. [1] J. Nuttall and H. L. Cohen Phys. Rev., 188, 1542 (1969) [2] T. N. Rescigno, M. Baertschy, D. Byrum and C. W. McCurdy Phys. Rev. A 55, 4253 (1997)
        Orateur: M. M.V. Volkov (Department of Physics, AlbaNova University Center,Stockholm University, 106 91 Stockholm, Sweden)
      • 15
        The driven Schroedinger approach to quantum scattering calculations
        Quantum scattering calculations on two and three-body systems with Coulomb interaction using the driven Schroedinger equation combined with the exterior complex scaling are discussed. Results for two-body scattering are reported, and the generalization to three-body scattering is considered.
        Orateur: Prof. Nils Elander (Stockholm University)
        Slides
    • Clusters; resonances
      • 16
        Interaction Blockade and Vortices in Atom Traps
        Many analogies exist between nanostructured quantum systems such as quantum dots, and trapped ultra-cold atom gases. The newly emerging "atomtronics" makes phenomena such as Bose-Einstein condensation accessible for the micro- and nano-design of future quantum devices. In this talk, we shall discuss how effects similar to Coulomb blockade in quantum dots may occur in systems of ultracold, trapped atoms [1-3]. We furthermore comment on vortices in single- and multi-component systems and point out the analogies between bosonic and fermionic quantum gases set rotating [4-6]. [1] K. Capelle, M. Borgh, K. Kärkkäinen and S.M. Reimann, Phys. Rev. Lett. 99, 010402 (2007) [2] M. Rontani, J. Armstrong, Y. Yu, S. Åberg and S.M. Reimann, arXiv:0806.3780 [3] P. Cheinet, S. Trotzky, M. Feld, U. Schnorrberger, M. Moreno-Cardoner, S. Foelling, and I. Bloch, arXiv:0804:3372 [4] S. Bargi, J. Christensson, G.M. Kavoulakis, and S.M. Reimann, Phys. Rev. Lett. 98, 130403 (2007). [5] J. Christensson, S. Bargi, K. Kärkkäinen, Y. Yu, G.M. Kavoulakis, M. Manninen and S.M. Reimann, New J. Phys. 10, 033029 (2008).
        Orateur: Prof. Stephanie Reimann (Lund University)
        Slides
      • 17
        Two-boson correlations in various one-dimensional traps
        A one-dimensional system of two trapped bosons which interact through a contact potential is studied using the optimized configuration interaction method. The rapid convergence of the method is demonstrated for a series of trapping potentials of convex and non-convex shapes. The energy spectra, as well as natural orbitals and their occupation numbers are determined in function of the interboson interaction strength. Various correlation characteristics are discussed in dependence both on the shape of the confining potential and on the sign and strength of the interaction. Entanglement properties are examined particularly carefully. In all the cases studied, a special attention is paid to the demonstration of the fermionization effects when the interaction becomes strong enough.
        Orateur: Prof. Anna Okopinska (University of Humanities and Sciences)
        Slides
      • 18
        Three-body decays of many-body resonances
        We discuss the three-body decay mechanisms of many-body resonances. Sequential decays proceed via two-body configurations after emission of the third particle. In direct decay all three particles leave simultaneously their interaction regions. The intermediate paths within the interaction regions are not observables and only accessible through models. The momentum distributions carry, apart from polarization, all possible information about decay modes and resonance structure. We use complex-scaled hyperspherical adiabatic expansion method to describe the three-body systems. The cases we use as examples (12C, 9Be and 6Be) present their own intriguing problems and they are moreover requested for astrophysical applications. When possible we compare our computed energy distributions with the experimental ones.
        Orateur: Dr Raquel Alvarez-Rodriguez (INFN Pisa)
        Slides
      • 16:45
        break
      • 19
        Theoretical investigation of the spectra of rotating trimers by means of a variational quantum method based in distributed Gaussian functions
        We have recently developed an approximate method to study the rovibrational spectra of molecular trimers, based in the use of distributed Gaussian functions (DGFs) to describe the interparticle distances [1,2]. The main assumption is to consider that rotation and vibration can be treated separately. The purely vibrational problem for a zero total angular momentum, J=0, is solved by means of an exact variational quantum approach which employs a set of triangular arrangements formed by the combination of DGFs for the R1, R2 and R3 coordinates [3]. The eigenstates of the J=0 case constitute the radial basis set to solve the rotational Hamiltonian. The method has been applied for the Ar3 system and the comparison with results from exact hyperspherical coordinate calculations [1, 4] reveals the validity of the approximation to describe the bound states for large values of the total angular momentum. [1] M. Márquez-Mijares, T. González-Lezana, O. Roncero, S. Miret-Artés, G. Delgado-Barrio and P. Villarreal, Chem. Phys. Lett. 460, 417 (2008). [2] I. Baccarelli, F. A. Gianturco, T. González-Lezana, G. Delgado-Barrio, S. Miret-Artés and P. Villarreal, Phys. Rep. 452, 1 (2007). [3] T. González-Lezana, S. Miret-Artés, G. Delgado-Barrio, P. Villarreal, J. Rubayo-Soneira, I. Baccarelli, F. Paesani and F. A. Gianturco, Comp. Phys. Comm. 145, 156 (2002). [4] F. Karlický, B. Lepetit, R. Kalus and F. X. Gadea, J. Chem. Phys. 126, 74305 (2007).
        Orateur: Dr Tomas Gonzalez-Lezana (Instituto de Fisica Fundamental, CSIC)
        Slides
      • 20
        Scattering processes in a framework of Faddeev approach
        Method of scattering calculations on three-body systems using differential Faddeev equations is discussed. An algorithm for calculating three-body resonances is considered and applied to the study of Helium trimer.
        Orateur: Prof. Elena Kolganova (Dubna, Russia)
        Slides
  • mercredi 15 octobre
    • Mathematical physics; exotic atoms
      • 21
        Can one bind three electrons with a single proton
        Orateur: M. Pierre Duclos (Centre de Physique Théorique, Marseille)
        Slides
      • 22
        Relativistic Hydrogen in Strong Magnetic Fields
        We study the bound states of relativistic hydrogen-like atoms cou- pled to strong homogeneous magnetic fields, under the assumption of an infinitely heavy nucleus. Working in the adiabatic approximation in which the electron is confined to the lowest Landau level, we show that the discrete spectrum is always non-empty and that, as the field strength increases, its eigenvalues successively descend into the lower part, ( −∞, −me c 2 ], of the continuous spectrum (me being the electron mass). This phenomenon is roughly periodical in log B. The question of the correct physical interpretation of this phenomenon will be posed. This talk is based on joint work with Philippe Briet and Pierre Duclos (Centre de Physique Théorique, Marseille, Luminy and Université du Sud Toulon-Var).
        Orateur: Prof. Raymond Brummelhuis (Birbeck, U. London, UK)
        Slides
      • 23
        A Mathematical Theory for Vibrational Levels Associated with Hydrogen Bonds
        We propose an alternative to the usual time--independent Born--Oppenheimer approximation that is specifically designed to describe molecules with Hydrogen bonds. In our approach, the masses of the Hydrogen nuclei are scaled differently from those of the heavier nuclei, and we employ a specialized form for the electron energy level surface. Consequently, anharmonic effects play a role in the leading order calculations of vibrational levels.
        Orateur: Prof. Alain Joye (Institut Fourier, Universite de Grenoble)
        Slides
      • 10:45
        break
      • 24
        Binding in some few-body systems containing antimatter
        The field generated by a fixed proton and antiproton a distance R apart is a particular example of a dipole field. The existence or otherwise of bound states of an electron (or a positron) in such a field was originally studied by Fermi and Teller and Wightman [1-3] in the late forties. They showed that if R > 0.639 a_0, a bound state of the system existed but if R < 0.639 a_0, no bound states existed. This result was confirmed in the mid-sixties by several authors, including Mittleman and Myerscough [4], Coulson and Walmsley [5] and Byers Brown and Roberts [6]. Crawford [7] obtained the interesting result that if R > 0.639 a_0, a countable infinity of bound states exists. It is of interest to consider what happens if an electron and a positron are both present in the dipole field. This system corresponds to H + Hbar with the positions of the nuclei fixed, as in the Born-Oppenheimer approximation. Armour et al. [8] were able to show that an upper bound to the R value below which no bound state of this system exists is 0.8 a_0. They did this using the Rayleigh-Ritz variational method and a basis set in prolate spheroidal coordinates similar to Kolos et al. [9], but with the addition of a function to represent very weakly bound positronium. More recently, Strasburger [10] has reduced this upper bound to 0.744 a_0, using a basis set made up of explicitly correlated Gaussian functions. As far as I am aware, no lower bound has been obtained for the above R value. A question of interest is whether a bound state of the the system containing the electron and the positron exists for R < 0.639 a_0, the critical value for each particle on its own in the presence of the nuclei. ................. More details in the latex-generated version. ............... If time permits, I will describe results of a preliminary investigation of the increase in the mass of the positron that would be necessary for it to form a bound state with a hydrogen molecule. The aim is to simulate conditions under which very large positron annihilation rates have been observed in low-energy positron scattering by some larger molecules. These very high rates are thought to be due to positron capture into vibrational Feshbach resonances of infrared-active modes [13]. References [1] E. Fermi and E. Teller, Phys. Rev. 72, 399 (1947). [2] A. J. Wightman, Phys. Rev. 77, 521 (1950). [3] J. E. Turner, J. Am. Phys. Soc. 45, 758 (1977). [4] M. H. Mittleman and V. P. Myerscough, Phys. Letts. 23, 545 (1966). [5] C. A. Coulson and M. Walmsley, Proc. Phys. Soc. (London) 91, 31 (1967). [6] W. Byers-Brown and R. E. Roberts, J. Chem. Phys. 46, 2006 (1967). [7] O. H. Crawford, Proc. Phys. Soc. (London) 91, 279 (1967). [8] E. A. G. Armour, V. Zeman and J. M. Carr, J. Phys. B 31, L679 (1998). [9] W. Kolos, D. L. Morgan, D. M. Schrader and L. Wolniewicz, Phys. Rev. A 11, 1792 (1975). [10] K. Strasburger, J. Phys. B 35, L435 (2002). [11] R. F. Wallis, R. Herman and H. W. Milnes, J. Molec. Spectroscopy 4, 51 (1960). [12] S. Jonsell, Private communication, 2005. [13] G. F. Gribakin and C. M. R. Lee, Phys. Rev. Lett. 97, 193201 (2006).
        Orateur: Prof. Edward A. G. Armour (School of Mathematical Sciences, University of Nottingham, Nottingham NG7 2RD, UK)
        Slides
      • 25
        Experimental low energy antiproton physics
        Experiments with low-energy antiprotons are currently performed at the antiproton Decelerator (AD) of CERN. The main focus of the three experimental collaboration is the study of fundamental symmetries, especially CPT invariance, using antiprotonic atoms and antihydrogen. The ASACUSA collaboration focusses on precision spectroscopy of antiprotonic helium, an exotic three-body system consisting of a helium nucleus, an electron and an antiproton. The antiproton occupies metastable states which allows precision determination of its mass and magnetic moment [1] by comparison to three-body QED calculations. Anthydrogen, the simplest neutral antimatter atom, promises CPT tests of highest precision by comparison to hydrogen, which is one of the best studied atoms. The ATRAP and ALPHA collaborations aim at producing and trapping antihydrogen in a neutral-atom trap and to measure the 1S-2S two-photon transition [2] to a precision similar to the one achieved for hydrogen (relative precision ~10-14 ). ASACUSA is preparing an experiment to measure the ground-state hyperfine structure of antihydrogen [3], the corresponding quantity for hydrogen being measured to relative precision of ~10-12 in the hydrogen maser. The AD delivers only pulsed beam which makes experiments of nuclear or particle physics type difficult. This restriction will not apply at the planned FLAIR facility [4] at FAIR, Darmstadt, where the availability of continuous antiproton beams at energies 100 times lower than at the AD will enable measurements not currently possible anywhere in the world. This talk will give an overview on current and planned experiments with low-energy antiprotons. [1] R.S. Hayano, M. Hori, D. Horvàth, and E. Widmann, Rep. Prog. Phys. 12, 1995 (2007). [2] G. Gabrielse, Adv. At. Mol. Opt. Phys. 50, 155 (2005). [3] E. Widmann, R. S. Hayano, M. Hori, and T. Yamazaki, Nucl. Instr. Meth. B 214, 31 (2004). [4] E. Widmann, Physica Scripta 72, C51 (2005).
        Orateur: Prof. Eberhard Widmann (Stefan Meyer Institute for Subatomic Physics, Vienna, Austria)
        Slides
    • Excursion
  • jeudi 16 octobre
    • Hadrons
      • 26
        New nuclear three-body clusters φN N
        Solving Faddeev differential equations, binding energies of three-body systems of the type φN N are calculated. Due to the strong attraction between φ-meson and nucleon, suggested in [1] and [2], bound states appear in systems φ + np (singlet and triplet), φ + nn and φ + pp. This indicates on the principal possibility of the formation of new nuclear clusters with increased number of nucleons. References [1] H. Gao, T.-S. H. Lee, and V. Marinov, Phys. Rev. C63, 022201 (2001). [2] F. Huang, Z. Y. Zhang , Y. W. Yu, ArXiv: nucl-th/0601003 (2006)
        Orateur: Prof. Vladimir B. Belyaev (JINR, Dubna, Russia)
        Slides
      • 27
        Variational calculations for K-few-nucleon systems
        Deeply bound KNN, KNNN and KNNNN states are discussed. The effective force exerted by the K meson on the nucleons is calculated with static nucleons. Next the binding energies are obtained by solving the Schrödinger equation or by variational calculations. The dominant attraction comes from the S-wave \Lambda(1405) and an additional contribution is due to \Sigma(1385). The latter state is formed at the nuclear peripheries and absorbs a sizable piece of the binding energy. It also generates new branches of quasi-bound states. The lowest binding energies based on a phenomenological KN input fall into the 40-80 MeV range for KNN, 90-150 MeV for KNNN and 120-220 MeV for K\alpha systems. The uncertainties are due to unknown KN interactions in the distant subthreshold energy region.
        Orateur: Prof. Slawomir Wycech (Soltan Institute for Nuclear Studies)
        Slides
      • 28
        A journey through exotica in hadronic physics
        The fascination with the exotic transcends all disciplines. Hadronic, or strong interaction physics has not been immune from it. Time and again it has come up with ideas of exotic hadrons. Time and again they turn out to be mirages. But then, once in a while, the exotic materializes, and all the past failures pale into the excitement of those discoveries. I will present a tour through some of these ups and downs of exotica in hadronic physics.
        Orateur: Prof. Kam Seth (Northwestern, Chicago, USA)
        Slides
      • 10:45
        break
      • 29
        Boundary-condition-determined wave functions, and their nodal structure, for few-electron atomic systems
        Highly compact wave functions with a clear physical meaning for the He atom and He-like isoelectronic ions for Z=1-10 are written as a symmetrized product of exp[(ar+br2)/(1+r)] electron-nucleus terms and an electron-electron Jastrow factor to satisfy the correct asymptotic behavior both at short and large interparticle distances. Some parameters are chosen to satisfy exactly the cusp-conditions, while the others are optimized by variational Monte Carlo calculations. The wave function energy is within 2 millihartrees from the non relativistic limit in the entire Z range, improving previously published work on similar compact wave functions. We tested the validity of the “coalescence wave function” approximation. The Z-dependence of the optimized parameters allows us to write a general form of the wave function, using Z as an explicit parameter and four parameters independent from Z. We checked the validity of this wave function on the case Z=30. For more than two electrons we investigate the nodal structures of atomic wave functions based on a product of spatial orbitals, namely Restricted, Unrestricted and Generalized Valence Bond wave functions. While the wave functions are different, their nodal structures are shown to be equivalent. This result is verified by fixed node-diffusion Monte Carlo simulations for atoms up to Ne. For 3 and 4 electrons we investigate the shape of the nodal structure while the nuclear charge approaches its critical value.
        Orateur: Prof. Dario Bressanini (Universita' dell'Insubria, Como, Italy)
        Slides
      • 30
        Microscopic Description of Few-Body Systems in the Fermionic Molecular Dynamics Approach
        The Fermionic Molecular Dynamics (FMD) [1] is a microscopic model for the description of nuclei in the p- and sd-shell. Many-body basis states are Slater determinants of Gaussian wave packets localized in phase space. The wave packet basis is very flexible and includes the harmonic oscillator shell model basis as well as Brink-type cluster states as limiting cases. The width of the wave packets is a variational parameter and allows to describe loosely bound halo nuclei. The intrinsic Slater determinants are projected on parity, angular momentum and total linear momentum to restore the symmetries of the Hamiltonian. We discuss the spectrum of 12C with a special emphasis on the structure of the first excited 0+ state, the famous Hoyle state. In the FMD approach the Hoyle state is found to be dominated by dilute alpha-cluster configurations, a picture that is confirmed by electron scattering data for the transition from the ground into the Hoyle state [2]. The FMD wave function can also be decomposed into N hbar Omega shell model configurations illustrating the highly coherent nature of the Hoyle state. As another application we present recent results for neon isotopes [3]. The low lying states of 17Ne and 18Ne can be understood essentially as systems of a 15O or 16O core and two protons in weakly bound s- or d-orbits. In FMD calculations we find in 17Ne a large admixture of spatially extended s^2 configurations explaining the large experimental charge radius. Higher lying excited states of 18Ne have 14O-4He cluster nature. Clustering becomes even more important in the heavier isotopes 19-22Ne. For example the parity doublets in 19Ne are related to the coexistence of 16O-3He and 15O-4He cluster configurations. [1] T. Neff and H. Feldmeier, Eur. Phys. J Special Topics 156, 69 (2008). [2] M. Chernykh, H. Feldmeier, T. Neff, P. von Neumann-Cosel and A. Richter, Phys. Rev. Lett. 98, 032501 (2007). [3] W. Geithner, T. Neff et al., to be submitted.
        Orateur: Dr Thomas Neff (GSI Darmstadt)
        Slides
    • T1
      • 31
        Four-quark stability
        In order to discuss the stability of four–quark states against dissociation into two isolated mesons we shall present in this talk an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We shall apply it to several physical systems of interest containing two heavy and two light quarks using different non–relativistic quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While (Q,Qnbar,nbar) states may be stable in nature, the stability of (Q,Qbar,n,nbar) states would imply the existence of quark correlations not taken into account by simple quark dynamical models. The possible role played by confining interactions not factorizable into simple two-body components will be discussed.
        Orateur: Dr Javier Vijande (University of Valencia)
        Slides
      • 32
        Proof of stability of tetraquarks in a minimal-path model of linear confinement
        The quark--antiquark confining potential, V2(r)=r (in appropriate units) is generalised to baryons as V3=min(d1+d2+d3), where di is the distance of the ith quark to a junction whose location is adjusted to minimise the interaction. Hence estimating V3 involves solving the famous Fermat--Torricelli problem. The extension to the tetraquark problem, initiated by several authors, has been recently revisited in Refs.~[1,2]. It consists of the minimum of (r13}+r24) and (r14+r23) on one side, which is the so-called “flip-flop” potential, and on the other side, (d15+d25+d56+d63+d64), with the junction points r5 and r6 optimised. This latter term is a Steiner minimal tree and it should be computed carefully and efficiently. This intricate four-body potential, inspired by the flux-tube limit of QCD, has been applied to solve the tetraquark problem for configurations (Q,Qbar,q,qbar)$ and (Q,Q,qbar,qbar) with two different masses M and m. From a careful variational calculation, it is found that the tetraquark ground-state is slightly bound for M=m, and, while the hidden-flavour state becomes unbound when M/m increases, the state with two units of heavy flavour becomes more stable. See the contribution by A. Valcarce and J. Vijande to this Workshop. A subtle property of minimal Steiner tree with four terminals gives a rigorous upper bound for the above four-body potential, and the four-body problem is exactly solvable with this upper bound. It is demonstrated that the flavour-exotic tetraquark is stable in the limit of large mass ratio M/m. [1] J. Vijande, A. Valcarce and J.M. Richard, Phys. Rev. D 76 (2007) 114013 [2] Cafer Ay, Jean-Marc Richard and J. Hyam Rubinstein, in preparation.
        Orateur: Prof. Jean-Marc Richard (LPSC, University of Grenoble, France)
        Slides JMR
      • 33
        Universality in low-energy few-body systems and leading corrections
        The zero range model with proper renormalization is a powerful too calculate a variety of interesting low-energy observables in nuclear and atomic physics. In the three-body sector this approach reveals many interesting features (such as approximate discrete scale invariance) of systems with large scattering length. In my talk I will discuss the zero-range in the more general context of effective field theories and address recent results for three-body recombination of identical bosons. Furthermore, I will explain how finite range effects modify such leading order results and show how the "leading order" discrete scale invariance constrains the impact of such effects.
        Orateur: Dr Lucas Platter (Ohio State University)
        Slides
      • 16:45
        break
      • 34
        Few-body Physics in Ultracold Gases: The Role of Efimov Physics
        In this talk, I will discuss general properties of few-body collisions and their influence on ultracold quantum gases in the regime where interatomic interactions are strongly affected by a Feshbach resonance. Since the early days of the achievement of Bose-Einstein condensation, it has been recognized that few-body processes are of crucial importance in determining the stability of condensates. Nevertheless, ultracold gases also offer an outstanding opportunity to explore one of the most counterintuitive quantum phenomena that manifest in a "simple" few-particle system: the Efimov effect. In fact, the first strong experimental evidence of Efimov physics was recently found in ultracold quantum gases as a giant loss of atoms causing the gas to become highly unstable. Nowadays, we know that Efimov physics affects three-body processes in experiments on ultracold quantum gases, and it now serves as a "guide" in the difficult task of achieving atomic and molecular stability. In this talk, I will outline some of my recent work on Efimov physics and also discuss some of its implications for the many-body behavior of ultracold quantum gases.
        Orateur: Dr Jose D'Incao (U. Colorado)
      • 35
        Few-body physics with ultracold Cs atoms and molecules
        Ultracold atomic gases are versatile systems to study few-body physics because of full control over the external and internal degrees of freedom. The scattering properties can be controlled because of the magnetic tunability of the two-body scattering length in the proximity of a Fes- hbach resonance and weakly bound dimers can be produced. Here, we experimentally explore three- and four-body physics by studying ultracold (30-250 nK) atom-dimer and dimer-dimer collisions with Cs Feshbach molecules in various molecular states and Cs atoms in different hyperfine states. An atom-dimer resonance is observed and interpreted as being induced by a trimer state, possibly an Efimov state [1]. A strong magnetic field dependence of the relaxation rate is also observed in a atom-dimer mixture made of non-identical bosons. Dimer-dimer in- elastic collisions have been studied in a pure, trapped sample of Feshbach dimers in the quantum halo regime. We identify a pronounced loss minimum with varying scattering length along with a further suppression of loss with decreasing temperature [2]. These observations provide insight into the physics of a few-body quantum system that consists of four identical bosons at large values of the two-body scattering length. References [1] S. Knoop, F. Ferlaino, M. Mark, M. Berninger, H. Sch ̈obel, H. -C. N ̈agerl, and R. Grimm, ” Observation of an Efimov-like resonance in ultracold atom-dimer scattering”, arXiv:0807.3306v1 [cond-mat] (2008). [2] F. Ferlaino, S. Knoop, M. Mark, M. Berninger, H. Sch ̈obel, H. -C. N ̈agerl, and R. Grimm, ” Collisions between tunable halo dimers: exploring an elementary four-body process with identical bosons”, Phys. Rev. Lett. 101, 023201 (2008).
        Orateur: Dr Francesca Ferlaino (Institut für Experimentalphysik and Institut für Quantenoptik und Quanteninformation, Innsbruck, Austria)
        Slides
      • 36
        Multiple scattering of light in cold atoms : from light localisation to plasma physics
        Cold atoms have emerged as ideal quantum system to study coherent transport properties of light. First experiments have established that dilute samples with large optical thickness allow studying weak localization of light. The present goal of this research is to study coherent transport of photons in dense samples. Anderson localization of light or superradiance are among the most interesting situation currently studied. The transition from coherent to incoherent transport is also studied, leading to investigations on anomalous diffusion (Levy flights) or random lasing (in the presence of strong pumping). Many of these aspects will be discussed and illustrated with recent experimental observations.
        Orateur: Robin Kaiser (CNRS)
        Slides
  • vendredi 17 octobre
    • T2
      • 37
        Spin solvent effects in doped helium clusters: A microscopic manifestation of superfluidity
        Doing a parallelism of nuclei/electrons with dopant/helium atoms, a quantum chemistry approach is used to perform spectral simulations of molecular species embedded in helium clusters of variable size. To account for the spin characteristics of the solvent, Hartree or Hartree-Fock methodology is applied to obtain energies and structural properties of the aggregates. In this frame, one considers the distortion induced on the molecular dopant by the surrounding helium atoms. As a consequence of the different spin multiplicity, inherent to the boson/fermion nature of the helium environment, selection rules for Raman[1] or infrared[2] spectra depending on the polar/non polar character of the dopant, predict completely different profiles in these diverse scenarios. This finding agrees with, e.g. the experimental infrared spectra of oxygen carbon sulfide, OCS, in helium nanodroplets[3]. Below the critical transition temperature of ⁴He, ~ 2.12 K, the boson profile is close to the gas phase spectrum of the dopant. So, the later seems to be freely rotating inside the droplet, a microscopic manifestation of superfluidity. In turn, even at lower temperatures (but above ~ 0.003 K, the superfluid transition temperature of ³He), the corresponding fermion spectrum shows an unstructured broad shape resembling the case of heavy molecules immersed in liquids. This peculiar behavior is illustrated through simulated spectra of the iodine chlorine (ICl) molecule, a species which mimics to the quasi-linear OCS molecule. References [1] D. López-Durán, M. P. de Lara-Castells, G. Delgado-Barrio, P. Villarreal, C. Di Paola,F. A. Gianturco, and J. Jellinek, Phys. Rev. Lett. {\bf 93}, 053401 (2004). [2] P. Villarreal, M. P. de Lara-Castells, R. Prosmiti, G. Delgado-Barrio, D. López-Durán, F. A. Gianturco, and J. Jellinek, Phys. Scr. {\bf 76}, C96 (2007). [3] S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science {\bf 279}, 2083 (1998).
        Orateur: Prof. PABLO VILLARREAL (INSTITUTO DE FISICA FUNDAMENTAL (CSIC))
        Slides
      • 38
        On the determination of the parameters of quantum resonances: theory and experiment
        Determination of the energy and the width of a resonance from experimental data is not an unambiguous procedure, in particular for broader resonances. Likewise, it is not unusual that different theoretical approaches to calculation of resonances result in somewhat different resonance parameters. In an attempt to clarify the situation we perform an investigation, using a simple model quantum system with a resonance (a particle in a potential well) as an example, where we simulate experimental determination of resonance parameters with the ordinary R-matrix method, and then compare these "experimental" parameters with those calculated using different theoretical approaches. The results tend to show that the different theoretical methods are in good agreement with each other (and with the "experiment") for narrow resonances but begin to disagree as the resonance width is increased. We argue that the disagreement is actually not due to some methods being "more precise" than others, but due to the inherent impossibility to uniquely define the resonance parameters as measurable physical observables.
        Orateur: Dmitri Fedorov (Aarhus University)
        Slides
      • 39
        Highly excited bound states and near-threshold resonances in ozone isotope effect
        The three-body recombination reaction, O_2 + O + M --> O_3 + M (1) is one of the central reactions of the Chapman cycle controlling the stability of the stratospheric ozone (O_3) layer. This reaction, in which O_3 is initially formed at dissociation threshold, is also responsible for large enrichments of heavy isotopomers of ozone. The enrichments, which seem unrelated to the natural abundances of oxygen isotopes and therefore are called “surprising”, are observed both in the field measurements and in the lab [1]. Despite numerous studies in the past few years, the isotope fractionations are still far from being satisfactorily explained and several essential questions remain to be solved [2]. In this talk I plan to discuss recent quantum mechanical studies of two unusual isotope dependences in reaction (1): Isotope Effect 1(IE-1), the dependence of the recombination rate on the difference of zero-point energies of the two fragmentation channels to which excited ozone can dissociate, i.e. X + YZ --> XYZ*-->XY + Z, where X, Y, and Z stand for the three isotopes of oxygen; Isotope Effect 2 (IE-2), the symmetry dependence of the recombination rate: the rate is smaller for symmetric molecules (e.g. XYX) than for non-symmetric ones (e.g. XXY). Both isotope effects, IE-1 and IE-2, will be analyzed using the full-blown quantum mechanical calculations of near-threshold resonance spectra as well as the cross-sections for collisional stabilization of ozone at dissociation threshold. It will be shown that the distributions of resonance widths in the rotating molecule and the peculiar topology of ozone interaction potential are able to explain most of the observed isotope dependences. [1] K. Mauersberger et al., Advances in Atomic, Molecular, and Optical Physics 50, 1 (2005). [2] R. Schinke, S. Yu.Grebenshchikov, M. V. Ivanov, and P. Fleurat-Lessard, Annu. Rev. Phys. Chem. 57, 625 (2006).
        Orateur: Prof. Sergy Yu. Grebenshchikov (Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen)
        Slides
      • 10:45
        break
      • 40
        Virtual states, halos and resonances in three-body atomic and nuclear systems
        A bi-dimensional map in the parameter space can be defined in the Efimov limit by the critical conditions for an excited state in three-body systems with two-identical particles. The scattering lengths of the two-body subsystems and one three-body scale define the parametric space. The border of the map encloses a region where excited states do exist (see ref. [1]). In this parameter space crossing the critical boundary, when at least one subsystem is bound, implies that an excited state becomes a virtual one [2] and a continuum resonance in the Borromean case. We show that these qualitative features are independent of mass ratios. The Borromean case of a three-boson continuum resonance was recently evidenced [3] in an experiment with trapped ultracold cesium gas near a Feshbach resonance. It is hoped that mixtures of different mass atoms in traps with tunable interactions allows to check the transition from Borromean to non-Borromean situations where a continuum resonance becomes bound and turns to a virtual state by changing the sign of the scattering length. In the nuclear context, one example is ^{20}C modeled as n-n-^{18}C} system with a s-wave short-range interaction between the pairs. Using a zero-range interaction we show that this system presents a virtual state that turns into an excited state when the ^{19}C binding is decreased [2]. Close to this condition, we also discuss the low-energy neutron-^{19}C$ elastic scattering. The s-wave phase-shift presents a zero corresponding to a pole of k cot delta in the complex plane. The pole is sensitive to the position of the excited bound or virtual state. We also discuss these results in the context of ultracold atomic systems of different species with tunable interactions. References: [1] T. Frederico and M. T. Yamashita, Nucl. Phys. {\bf A} 790, 116c (2007). [2] M. T. Yamashita, T. Frederico and L. Tomio, Phys. Rev. Lett. {\bf 99}, 269201 (2007); Phys. Lett. B {\bf 660}, 339 (2008). [3] T. Kraemer et al., Nature {\bf 440}, 315 (2006).
        Orateur: Prof. Tobias Frederico (ITA, São José dos Campos, Brazil)
        Slides
      • 41
        Multiparticle interactions of zero-range potentials
        For two particles it is often convenient to replace local or non-local potentials by zero-range interactions. Since they are zero-range, these interactions can often be replaced by boundary conditions at a point where the separation between two particles vanishes. In either case, zero-range potentials are useful when the details of the interaction at small distances are not critical for the dynamics. The description of Bose condensates is an example where zero-range interactions are basic to theories of the condensed aggregates. These theories employ the model interactions to obtain a mean field description of large numbers of particles. On a more fundamental level, zero-range interactions are employed to model the interactions of three particles, where they have been used to study the properties of loosely-bound Efimov states. Owning to their success in these areas they have been generalized to allow for multichannel interactions, interactions for states with non-zero angular momentum and energy dependent zero-range potentials. Properties of these generalized potentials and their applications will be illustrated for the interaction of three particles at vanishingly small kinetic energy.
        Orateur: Joseph Macek (University of Tennessee and Oak Ridge National Laboratory)
        Slides
    • T3
      • 42
        Behavior of Wave Functions near the Thresholds.
        Orateur: Dr Dmitry Gridnev (Post Doc)
        Slides
      • 43
        The Hyperspherical Harmonic method for a A-body system without permutation symmetry
        The Hyperspherical Harmonic (HH) method has been widely used in nuclear physics to describe nuclei with A=3,4 [1]. The extension to larger systems is hampered by the large degeneracy of the HH basis. The construction of specifically anti-symmetric states reduces the dimensionality of the basis but encounters technical and numerical difficulties. The coefficients of anti-symmetric basis elements, constructed as a linear combination of HH basis elements times appropriate spin-isospin vectors, are the more difficult to obtain the larger the number of basis elements and/or the number of particles considered; however, once the basis has been anti-symmetrized, the solution of the Schroedinger equation becomes much easies because the potential energy matrix elements can be calculated efficiently. In the present talk we would like to discuss the possibility of using the HH method without resorting to the construction of anti-symmetrized basis states. The obvious disadvantage of the proposed approach is in the very large basis that one needs to handle, which has to be balanced with the simplicity of avoiding the initial construction of anti-symmetric basis states; the physical basis states, having the desired symmetry, are automatically generated in the diagonalization of the Hamiltonian. Preliminary results for the discrete states of A=3,4 systems will be shown using a simple nucleon-nucleon potential. [1] A. Kievsky, S. Rosati, M. Viviani, L.E. Marcucci, and L. Girlanda; J. Phys. G: Nucl. Part. Phys. 35 (2008) 063101
        Orateur: Dr Mario Gattobigio (Institut Non Lineaire de Nice - Universite de Nice)
        Slides
      • 44
        Scattering states of three-body systems with the Hyperspherical Adiabatic method
        Orateur: Dr Paolo Barletta (University College London, London, UK)
        Slides
      • 16:45
        break
      • 45
        Theory of Classical and Quantum Reaction Dynamics in Multidimensional Systems
        Orateur: Prof. Holger Waalkens (Department of Mathematics, University of Groningen, Nijenborgh 9, 9747 AG Groningen, the Netherlands)
        Slides
      • 46
        Efimov Effect in 2-Neutron Halo Nuclei
        Orateur: Dr Indranil Mazumdar (Tata Institute Of Fundamental Research, Mumbai)
        Slides
      • 47
        Discussion: workshop summary, next workshop
    • Banquet
Fonctionne avec Indico v3.2.8