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Séminaires 2012 (physique nucléaire)

Mercredi 12 Décembre 2012
From nuclear droplets to compact stars : Thermodynamics of dilute clusterized matter
Panagiota PAPAKONSTANTINOU (Groupe Théorie, IPN Orsay)
The extent to which we can describe reliably the nuclear equation of state in different thermodynamical domains determines whether we can make the most of new observational data on neutron-star properties, computationally demanding supernova simulations, and even the anticipated detection of gravitational waves - with important implications for diverse fields of physics. In this seminar I will focus on the description of baryonic matter at sub-saturation densities and low temperatures, where nuclei (or clusters) and a gas of nucleons are expected to coexist and interact with each other and with surrounding leptons. I will present a simple, but microscopically motivated model for heavy clusters, and a potentially unified description of light and heavy clusters. I will discuss the relevance of such studies in the evolution of core-collapse supernovae and give perspectives for future developments.

Mercredi 28 Novembre 2012
Two-nucleon scattering in effective field theory : searching for the power counting
Manuel PAVÓN VALDERRAMA (Groupe Théorie, IPN Orsay)
In this talk I will consider the two-nucleon system from the effective field theory viewpoint. In particular, I address the problem of constructing a sensible expansion of the scattering amplitude that is able to reconcile the requirements of (i) renormalizability, (ii) the existence of a well-defined power counting at the level of observable quantities and (iii) phenomenological success. Using as a starting point a proposal by Nogga, Timmermans and van Kolck, I show how these conditions can be met by perturbatively renormalizing the chiral two pion exchange contributions to the nuclear force. The explicit next-to-next-to-leading order computations show that the present scheme leads to a good description of the phase shifts, comparable with the results obtained in the Weinberg counting at the same order, but free of the usual inconsistencies generated by the full iteration of chiral nuclear forces. Further aspects of the theory, such as the convergence rate, the expansion parameter, or the power counting in deuteron reactions, will be briefly discussed.

Mercredi 14 Novembre 2012
Spin-aligned neutron-proton pairs in N=Z nuclei
The study of nuclei with equal numbers of neutrons and protons (N = Z) is one of the declared objectives of radioactive-ion-beam facilities. Currently, N = Z experiments are approaching 100Sn, involving studies of nuclei where nucleons are dominantly confined to the 1g_9/2 orbit. In this talk it is shown that the aligned neutron-proton pair with angular momentum J=9 and isospin T=0 plays a central role in the low-energy spectroscopy of the N Z nuclei in this mass region. This observation is made by analyzing shell-model wave functions in terms of a variety of two-nucleon pairs with different angular momentum J and isospin T. On the basis of these results one concludes that a simple model can be formulated in terms of isoscalar bosons with J=9. Due to its simplicity, such a model could be of use to elucidate the main structural features of N Z nuclei in this mass region. Examples of simple predictions resulting from this approach are discussed.

Mercredi 24 Octobre 2012
Pairing correlations : from finite nuclei to the crust of neutron stars
Alessandro PASTORE (IPN, Lyon)
Pairing correlations influence the basic properties of atomic nuclei in an essential way. They are important to explain phenomena like odd-even mass staggering, low-lying quadrupole states or moments of inertia. All these phenomena become even more important for nuclei very far from the stability valley of the nuclear chart. In this seminar I will investigate within the framework of a mean-field approach based on the phenomenological Skyrme functional, the superfluid properties of nuclei with a Fermi energy close to zero. Such subject has been recently investigated in different articles in finite nuclei [1,2] and in Wigner-Seitz cells [3,4], showing the role of resonant and continuum states on pairing correlations for such exotic systems.
[1] P. Schuck and X. Viñas, Phys. Rev. Lett. 107, 205301 (2011)
[2] A. Pastore, J. Margueron, X. Viñas and P. Schuck (in preparation) (2012)
[3] A. Pastore, S. Baroni and C. Losa, Phys. Rev. C 84 , 065807, (2011)
[4] A. Pastore, (Submitted to Phys. Rev. C)

Mardi 23 Octobre 2012
Microscopic Study of the Isoscalar Giant Monopole Resonance in Cd, Sn and Pb Isotopes
Ligang CAO (Institute of Modern Physics, Lanzhou)
The isoscalar giant monopole resonance (ISGMR) in Cd, Sn and Pb isotopes is studied within the self-consistent Skyrme Hartree-Fock+BCS and quasi-particle random phase approximation (QRPA). Three Skyrme parameter sets (SLy5, SkM*, SkP) are used in the calculations, since they are characterized by different values of the compression modulus in symmetric nuclear matter (K_infty=230, 217, and 202 MeV, respectively). We also investigate the effect of different types of pairing forces on the ISGMR in Cd, Sn and Pb isotopes. The calculated energies and the strength distributions of ISGMR are compared with available experimental data. We find that SkP underestimates the various energies for all isotopes due to its low value of the nuclear matter incompressibility, namely K_infty=202 MeV. However, it can give a better description on the constrained energies for Cd isotopes and a reasonable peak energy for some nuclei. On the other hand, the SLy5 parameter set, supplemented by an appropriate pairing interaction, gives a reasonable description of the scaling energies in Cd, Sn isotopes and a good centroid energies in Pb isotopes. A better description of ISGMR in Cd and Sn isotopes is achieved by the SkM* interaction, which has a somewhat softer value of the nuclear incompressibility.

Mercredi 17 Octobre 2012
Competition between pairing and condensation in resonant Bose-Fermi mixtures
Pieri PIERBIAGIO (University of Camerino, Italy)
The properties of a Bose-Fermi mixture, with the boson-fermion interaction tuned by a broad Fano-Feshbach resonance will be discussed. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling, thus revealing a quantum-phase transition. The critical coupling is found to depend weakly on the density imbalance and rather strongly on the mass ratio. The bosonic momentum distribution function at sufficiently large density imbalance shows a peculiar ``Pauli exclusion" effect due to the simultaneous presence of composite fermions and unpaired fermions. Results obtained with both many-body diagrammatic theory [1,2] and fixed-node Quantum Monte-Carlo methods [3] will be presented.
[1] E. Fratini, P. Pieri, Phys. Rev. A 81, 051605 (2010)
[2] E. Fratini, P. Pieri, Phys. Rev. A 85, 063618 (2012)
[3] G. Bertaina, E. Fratini, S. Giorgini, P. Pieri, V. Savona, in preparation

Mercredi 27 Juin 2012
A study of pairing correlations for weakly-bound systems at the drip lines in a simple one-dimensional model
Andrea VITTURI (Dipartimento di Fisica e Astronomia, Universita di Padova, Italy)
The physical case of Borromean nuclei is modelized in terms of an inert core plus two particles moving in a mean-field one-dimensional potential and interacting via a density-dependent residual delta interaction. The model assumes that, due to the vicinity of the drip line, all bound single-particle levels are occupied by the core particles and therefore all the unperturbed additional two-particle states lie in the continuum. The two-particle system becomes bound due to the action of the residual delta interaction. Different methods are used to construct the twoparticle basis and their convergence properties are discussed. One calculates the particle-hole and particle- particle response functions to this correlated system, relevant for describing breakup, knock-out and two-particle transfer processes, and study their convergence as a function of the box radius. As an example, the two-particle break-up process is calculated and discussed. The peculiarities and the characteristics of the correlated weak-binding situation show up clearly in this one-dimensional case and are supposed to persist in the extension to the more realistic three-dimensional case.

Mercredi 20 Juin 2012
Thermodynamics properties of small systems with fixed particle number
The thermodynamics properties of small systems with fixed particle number are studied by using the Variation After Projection approach at finite temperature. The method, that was never applied before due to its complexity, is applied to obtain a canonical description of the pairing properties of odd and even systems. The comparison with the exact solution in the case of the Richardson model shows that this method provides a very good description both at very low and high temperature, overcoming thus the limitations observed in other mean- field based approaches. Possible approximated schemes to be adopted in order to study larger systems will be also discussed.

Mercredi 13 Juin 2012
Puzzling behaviour of 212Po
A. ASTIER (CSNSM Orsay) et D. DELION (NIPNE Bucharest)
While the first excited states and the E2 transitions of 210 Pb128 and 21084Po are well described within the shell model approach, the behaviour of 21284 Po128 is puzzling. For instance, the excitation energies of its low-lying positive-parity states are not far from the ones of 210Pb or 210Po, but the B(E1) values are one order of magnitude higher than those of 210Po. The first part of the seminar will be devoted to the experimental discovery of a new class of excited states of 212Po which have a non-natural parity and are connected by enhanced E1 transitions to the already-known yrast states. A comprehensive description of three sets states [1]. A comprehensive description of three sets of experimental results of 212Po will be given in the second part : the absolute alpha-decay width of its ground state, the large E2 transition strengths within its yrast states, and the large B(E1) values of the transitions connecting the new 4-, 6-, 8- states to the 4+, 6+, 8+ yrast states. In this work, the non-natural parity states are analyzed in terms of the collective octupole excitation in 208Pb coupled to positive parity states of 210Pb and the B(E1) transition strengths are described by adding an alpha-cluster component which is the same as that involved in the calculations of the absolute alpha-decay width and the B(E1) values. absolute alpha-decay width and the B(E1) values [2].
[1] A. Astier, P. Petkov, M.-G. Porquet, D.S. Delion, and P. Schuck, Phys. Rev. Lett. 104 (2010) 042701.
[2] D.S. Delion, R.J. Liotta, P. Schuck, A. Astier, and M.-G. Porquet, Phys. Rev. C, in press.

Mercredi 23 Mai 2012
Spontaneous generation of spin-orbit coupling in magnetic dipolar Fermi gases
Takaaki SOGO (Groupe Théorie, Institut de Physique Nucléaire Orsay )
In this talk I will present our recent work published in [1]. In this paper, the stability of an unpolarized two-component dipolar Fermi gas is studied within mean-field theory. Besides the known instability towards spontaneous magnetization with Fermi sphere deformation, another instability towards spontaneous formation of a spin-orbit coupled phase with a Rashba-like spin texture is found. A phase diagram is presented.)
[1] T. Sogo, M. Urban, P. Schuck, and T. Miyakawa, Phys. Rev. A 85, 031601(R) (2012).

Mercredi 16 Mai 2012
Four-particle (alpha-like) correlations in nuclear systems
Gerd ROEPKE (Universität Rostock, Allemagne)
Correlations are significant for the properties of nuclear systems at low densities and moderate temperatures. Continuum correlation as well as bound state formation and quantum condensates are investigated in a systematic quantum statistical approach. In contrast to pairing that is well understood, quartetting is a new feature of low-density matter. Recent experimental results with heavy ion reactions at moderate energies are presented that show the Mott effect of light nuclei. The symmetry energy at low densities is obtained. Consequences of quartetting for nuclear structure are discussed. Few-nucleon correlations are of relevance in astrophysical processes like supernova explosions.

Mercredi 9 Mai 2012
Elementary excitations in homogeneous Neutron Star Matter
Marcello BALDO (INFN, Catania)
The elementary excitations of superfluid matter below the crust of Neutron Stars are relevant for many phenomena and properties, like neutrino mean free path, heat capacity, thermal conductivity and others. I will present a study of the spectral functions of these elementary excitations. The theory is based on the conserving approximation scheme, generalized to the superfluid case. We apply the method to the proton and electron components, where both pairing and Coulomb interactions are introduced. The interplay of these two interactions in determining the overall structure of the spectrum and of the corresponding strength functions is discussed in detail. I will discuss the appearance of a pseudo-Goldstone mode, characterized by a sharp peak in the strength function, and whose velocity is determined by both Coulomb and pairing interactions. This mode merges into the usual Goldstone mode when the Coulomb interaction is switched off, i.e., in pure superfluid where it is a consequence of the breaking of gauge invariance. Also the branch corresponding to the pair-breaking mode is clearly identified. The pseudo-Goldstone and the pair-breaking mode undergo a quasi-crossing close to twice the pairing gap Delta above which, at increasing values of the momentum the upper pseudo-Goldstone branch merges into the sound mode of the normal fluid, while the lower pair-breaking mode corresponds to the over-damped mode also present in the normal fluid. At increasing values of the pairing gap the spectrum above 2 Delta shrinks and finally disappears at large enough value of the gap. Besides these branches, the electron plasmon appears at higher energy. Even at moderately values of the gap, such as 100-200 keV, the electron plasmon mode actually disappears. The nuclear particle-hole interaction for the proton component is briefly discussed and it is argued that its role is marginal.

Vendredi 4 Mai 2012
Cluster and Pasta Stuctures in the Skyrme-Force Mean-Field Theory
Joachim MARHUN (University of Frankfurt)
We have investigated the presence of alpha-clustering in light nuclei within the mean field theory. It is found that a pronounced alpha-clustering can be present for very light nuclei, but goes away as the spin-orbit and Coulomb forces become more important. The possibility of chain-like alpha-cluster configurations in systems such as 12C and 16O was also investigated and it was found that such structures may be stabilized by rotation. A similar stabilization was observed in toroidal nuclei. In related studies we found that the well-known pasta structure of nuclear matter is also reproduced by time-dependent calculations starting from an alpha gas, with usually rapid approach to thermal equilibrium. This also opens the possibility of studying the stability of such structures with respect to collective vibrations.

Mercredi 25 Avril 2012
Casimir effect, dark energy and van der Waals forces
Joseph CUGNON (Université de Liège, Belgique)
The Casimir effect is usually interpreted as arising from the modification of the zero point energy of QED when two perfectly conducting plates are put very close to each other, and as a proof of the ’reality’ ; of this zero point energy. The Dark Energy, necessary to explain the acceleration of the expansion of the Universe is sometimes viewed as another proof of the same reality. Recently, several physicists have challenged the usual interpretation, arguing that the Casimir effect should rather be considered as a ’giant’ van der Waals effect. All these aspects are shortly reviewed.

Mercredi 28 Mars 2012
Beyond the No Core Shell Model : Extending the NCSM to Heavier Nuclei
Bruce R. BARRETT (Department of Physics, University of Arizona, Tucson)
The ab initio No-Core Shell Model (NCSM) has been successful in providing a microscopic description of light nuclei (i.e., A ≤ 20), based upon the fundamental two- and three-body interactions among the A nucleons inside the nucleus. The main challenge facing future NCSM investigations is how to extend this approach to medium- and heavy-mass nuclei, for which the sizes of the model spaces required to obtain converged results become unmanageable for not only existing but also for near-future computers. New approaches for attacking this problem will be presented and discussed : 1) the use of the NCSM approach to generate the microscopic input for Standard Shell Model calculations (the so-called ab initio Shell Model with a Core), which can then be performed for sd- and pf-shell nuclei ; 2) the utilization of a new importance truncation approach, which allows for the reduction to a tractable size of the required model spaces to obtain converged NCSM results ; and 3) the application of an Effective Field Theory with only nucleon fields directly in the NCSM model spaces, so as to construct effective interactions suitable for many-body calculations.

Mardi 20 Mars 2012
Pairing correlations and anti-halo effect in weakly bound nuclei
Hiroyuki SAGAWA (University of Aizu, Japan)
Pairing correlations are known to be important in nuclei throughout the periodic table, giving an extra binding for paired nucleons [1,2]. They play an essential role especially in loosely bound nuclei such as 11Li and 6He (the so called Borromean nuclei), because the nuclei would be unbound without the pairing correlations. It is known that many-body correlations strongly modify the pure mean-field picture of loosely bound nuclei. It may happen that the strong pairing correlations do not allow the decoupling of weakly bound nucleons from the core nucleus and prevent the growth of halo structure. This pairing "anti-halo" effect has been suggested with a Hartree-Fock Bogoliubov (HFB) model [3], but a clear experimental signature of the anti-halo effect has not yet been obtained so far. Because of these circumstances, it is highly desirable to explore whether the odd-even staggering observed in the recent experimental data for the reaction cross sections of neutron-rich Ne isotopes [4] is an evidence for the pairing anti-halo effect. In order to address this question, we study neutron-rich Ne isotopes using the HFB method. We further study a possible anti-halo effect of neutron-rich C and O isotopes using a three-body model given in Ref. [5,6].
[1] A. Bohr and B.R. Mottelson, Nuclear Structure (Benjamin, Reading, MA, 1975), Vol.I.
[2] D.M. Brink and R.A. Broglia, Nuclear Superfluidity : Pairing in Finite Systems (Cambridge University Press, Cambridge, England, 2005).
[3] K. Bennaceur, J. Dobaczewski and M. Ploszajczak, Phys. Lett. B496, 154 (2000).
[4] M. Takechi et al., Nucl. Phys. A834, 412c (2010) ; Phys. Lett. B707, 357 (2012) and private communication.
[5] K. Hagino and H. Sagawa, Phys. Rev. C72, 044321 (2005) ; C75, 021301 (2007).
[6] K. Hagino and H. Sagawa, Phys. Rev. C84, 011303 (2011) ; C85, 014303 (2012).

Mercredi 7 Mars 2012
Faddeev Random Phase Approximation for the self-energy
Matthias DEGROOTE (Center for Molecular Modelling, Ghent University)
The Faddeev Random Phase Approximation (FRPA) [1,2] is a Green’s function method which couples collective degrees of freedom to the single particle motion by re-summing an infinite number of Feynman diagrams. The Faddeev technique is applied to describe the two-particle-one-hole (2p1h) and two-hole-one-particle (2h1p) Green’s function in terms of non-interacting propagators and kernels for the particle-particle (pp) and particle-hole (ph) interactions. This results in an equal treatment of the intermediary pp and ph channels. In FRPA the phonons are calculated on the random phase approximation (RPA) level. The method shows close resemblance to the Algebraic Diagrammatic Construction method of third order (ADC(3))[3] which is retrieved when inserting TDA phonons instead of RPA phonons[4]. The presentation will focus on the derivation of the FRPA formalism and the diagrammatical content of the method. There will also be some attention to the extension of the method to other kernels and the link with the self-consistent RPA (SCRPA).
1. C. Barbieri and W.H. Dickhoff, Phys. Rev. C 63, 034313 (2001)
2. C. Barbieri, D. Van Neck and W.H. Dickhoff, Phys. Rev. A 76, 052503 (2007)
3. J. Schirmer, L.S. Cederbaum, O. Walter, Phys. Rev. A 28, 1237 (1983)
4. M. Degroote, D. Van Neck and C. Barbieri, Phys. Rev. A 83, 042517 (2011)

Mercredi 29 Février 2012
Nuclear physics on the lattice
Evgeny EPELBAUM (Ruhr Universität, Bochum )
Chiral effective field theory provides a systematic framework to low-energy dynamics of few-nucleon systems and light nuclei based on (the symmetries of) QCD. Using a discretized version of this approach by treating pions and nucleons as point-like particles on an Euclidean space-time lattice allows to evaluate the path integral by Monte Carlo sampling and to access the properties of heavier systems. I describe the foundations of this method and consider the applications to the spectra of light nuclei.

Mercredi 22 Février 2012
Of pygmy resonances and other demons
Panagiota PAPAKONSTANTINOU (Groupe Théorie, Institut de Physique Nucléaire, Orsay)
Despite many years of theoretical and experimental efforts, the nature of low-energy E1 strength, observed below the giant dipole resonance, remains largely unclear, even for stable nuclei. Issues like collectivity, fragmentation, relation to nuclear-matter properties, are still under debate. Adding to the problem is a semantics mess of sorts : the associated term "pygmy" is often applied loosely and according to accessible energetic region, proposed interpretation, or convenience. Recent and upcoming measurements of complete E1 spectra in stable nuclei and new experiments with radioactive beams hold the promise of clarifying several of the persisting questions, on the condition of sound theoretical support, as well as a clear definition of the problem at hand.
In this context, I will discuss the dipole response of, mainly, the Ca and Sn isotopic chains. Systematic calculations using standard theoretical tools, in particular the Quasi-particle Random Phase Approximation, will confront the available data with enlightening results. We will see, among other things : the importance of obtaining complete E1 spectra ; why different probes, including isoscalar ones, are necessary to determine unambiguously the origin of strength ; that a single mechanism, such as a neutron-skin mode, cannot account for the richness of the dipole spectrum at low energies ; that nevertheless a simple picture does seem to emerge at the lowest end of the spectrum.

Mercredi 15 Février 2012
Three different approaches of the same NN interaction : the Yukawa model in nuclear physics
Jaume CARBONELL (LPSC Grenoble et IRFU/SPhN Saclay)
After a brief discussion of the meaning of an "interaction potential" in quantum mechanics, we shall examine the predictions of the Yukawa model (scalar meson exchange) for the nucleon-nucleon interaction in three different dynamical frameworks :
- the non relativistic dynamics of the Schr\"odinger equation
- the relativistic quantum mechanics of the Bethe-Salpeter and Light Front equations
- the lattice solution of the Quantum Field Theory, obtained in the "quenched" approximation.

Mercredi 8 Février 2012
Growth of magnetic fields in accreting millisecond pulsars : the case of J1823-3021A
Alessandro DRAGO (Università di Ferrara, Italie)
The Fermi LAT collaboration has recently reported the discovery of the pulsations of the gammaray pulsar J1823-3021A with a luminosity which is the highest observed to date for any millisecond pulsar [1]. This large luminosity implies a large spin down rate dP/dt and therefore a large magnetic field which seems to be incompatible with the observed short rotation period P. Here we discuss two possible explanations for the observed P and dP/dt : (a) to assume a very small radius for the star ; (b) to considere the increase of the external magnetic field due to the diffusion of an internal magnetic field generated by r-modes during mass accretion. The first scenario strongly constrains the equation of state of high density matter and it implies that J1823-3021A is a quark star, but is based on rather extreme astrophysical conditions. The second scenario instead does not require any ad hoc assumption and is viable both for neutron and quark stars. Our analysis therefore suggests the formation of a strong magnetic field inside accreting compact stars and it provides a new evolutionary path for these objects.
[1] Science 334, 1107 (2011).

Mardi 31 Janvier et Mardi 7 Février 2012
Lectures : Solitons in nuclear physic
Alessandro DRAGO (Università di Ferrara, Italie et Professeur invité Paris-Sud XI)
In these lectures I will introduce the idea of solitons and I will discuss their relevance in hadronic and in nuclear physics. Solitons are non-perturbative and non-dissipative solutions of a field theory and they play an important role in describing the structure of single hadrons. The most famous soliton in this context is the Skyrmion, which I will discuss in my lectures. Many attempts have been made to describe also an atomic nucleus as a multi-soliton system and I will discuss the problems and the perspectives. The following points will be examined :
-What is a soliton and the necessary conditions for having solitonic solutions from a field theory
-Topological versus non-topological solitons
-A simple example : the sine-Gordon soliton
-Large Nc limit
-The Skyrme model
-Hybrid chiral-quark solitons
-A lattice of solitons to describe atomic nuclei

Mercredi 1er Février 2012
Ab initio take on the definition, meaning and usefulness of effective single-particle energies in nuclei
The concept of single-nucleon shells dates back to the early days of nuclear physics and constitutes the basic pillar of the nuclear shell model and of our understanding of nuclear structure. This presentation will address the definition, the meaning, and the usefulness of effective single-particle energies (ESPEs) in doubly closed shell nuclei from the perspective of one-nucleon transfer reactions. Specifically, several points of interest will be discussed and illustrated through ab-initio coupled-cluster calculations of oxygen and calcium isotopes. Those points are (i) the impact of correlations on both ESPEs and one-nucleon separation energies, (ii) the error made by computing/extracting ESPEs approximately, (iii) to which extent ESPEs are "observable" and (iv) to which extent observables, e.g. one-nucleon separation energies and the energy of the first excited 2+, are correlated with the size of the gap at the Fermi energy in the ESPE spectrum.

Lundi 23 Janvier 2012
Chiral effective field theory for nuclear matter
Jose A. OLLER (Universidad de Murcia, Espagne)
We report on the recent developments of a new effective field theory for nuclear matter. We present first the nuclear matter chiral power counting that takes into account both short- and long-range inter-nucleon interactions. It also identifies non-perturbative strings of diagrams, related to the iteration of nucleon-nucleon interactions, which have to be re-summed. The methods of unitary chiral perturbation theory have been shown to be a useful tool in order to perform those resummations. Results up to next-to-leading order for the ground state energy per particle of nuclear matter, the in-medium chiral quark condensate, pion self-energy and axial-vector couplings of the pion are discussed. The equation of state of pure neutron matter is applied to calculate the maximum mass for neutron stars.

Mercredi 18 Janvier 2012
Lattice QCD confronts experimental nuclear physics
Silas BEANE (University of New Hampshire, Durham (USA))
After a basic introduction to lattice QCD, I will discuss recent progress in calculating nuclear physics interactions and properties using lattice QCD, with an emphasis on a few benchmarking calculations. I will then focus on several areas in which lattice QCD will soon be competitive with experiment ; specifically, I will consider nuclear parity violation and the simplest hypernuclear processes.

Mercredi 11 Janvier 2012
Spin scissors mode and the fine structure of m1 states in nuclei
The coupled dynamics of low lying modes and various giant resonances are studied with the help of the Wigner Function Moments method generalized to take into account spin degrees of freedom. Equations of motion for collective variables (quadrupole moments of neutrons and protons with different spin projections, their angular momentums and Fermi surface deformations) are derived on the basis of TDHF equations in the harmonic oscillator model including spin orbit potential plus quadrupole-quadrupole residual interaction. Introducing spin allows one to find new types of the nuclear collective motion in addition to the well known nuclear scissors and giant resonances.

Mardi 10 Janvier 2012
Some new applications of the variational approach to nuclear problems
Arthur K. KERMAN (MIT)



Institut de Physique Nucléaire Orsay - 15 rue Georges CLEMENCEAU - 91406 ORSAY (FRANCE)
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