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N. Michel

Publications and source records attributed to N. Michel.

102 records · Page 6Linked to original sources
arXiv2006

Density matrix renormalization group approach for many-body open quantum systems

The density matrix renormalization group (DMRG) approach is extended to complex-symmetric density matrices characteristic of many-body open quantum systems. Within the continuum shell model, we investigate the interplay between many-body configuration interaction and coupling to open channels. It is shown that the DMRG technique applied to broad resonances in the unbound neutron-rich nucleus 7He provides a highly accurate treatment of the coupling to the non-resonant scattering continuum.

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arXiv2006

Continuum coupling and spectroscopic properties of nuclei

The nucleus is a correlated open quantum many-body system. The presence of states that are unbound to particle emission may have significant impact on spectroscopic properties of nuclei, especially those close to the particle drip lines. In the framework of the continuum shell model in the complex momentum-plane, we discuss salient effects of the continuum coupling on the spectroscopic factors, one-neutron overlap integrals, and energies of excited states in $^{6}$He and $^{18}$O. We demonstrate the presence of non-perturbative threshold effects in many-body wave functions of weakly-bound and unbound states.

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arXiv2004

Proton-Neutron Coupling in the Gamow Shell Model: the Lithium Chain

The shell model in the complex k-plane (the so-called Gamow Shell Model) has recently been formulated and applied to structure of weakly bound, neutron-rich nuclei. The completeness relations of Newton and Berggren, which apply to the neutron case, are strictly valid for finite-range potentials. However, for long-range potentials, such as the Coulomb potential for protons, for which the arguments based on the Mittag-Leffler theory do not hold, the completeness still needs to be demonstrated. This has been done in this paper, both analytically and numerically. The generalized Berggren relations are then used in the first Gamow Shell Model study of nuclei having both valence neutrons and protons, namely the lithium chain. The single-particle basis used is that of the Hartree-Fock-inspired potential generated by a finite-range residual interaction. The effect of isospin mixing in excited unbound states is discussed.

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arXiv2004

Gamow Shell-Model Description of Weakly Bound and Unbound Nuclear States

Recently, the shell model in the complex k-plane (the so-called Gamow Shell Model) has been formulated using a complex Berggren ensemble representing bound single-particle states, single-particle resonances, and non-resonant continuum states. In this framework, we shall discuss binding energies and energy spectra of neutron-rich helium and lithium isotopes. The single-particle basis used is that of the Hartree-Fock potential generated self-consistently by the finite-range residual interaction.

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arXiv2004

Structure of Exotic Nuclei

The progress in the modeling of exotic nuclei with an extreme neutron-to-proton ratio is discussed. Two topics are emphasized: (i) the quest for the universal microscopic nuclear energy density functional and (ii) the progress in the continuum shell model.

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arXiv2003

Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States

We present the study of weakly bound, neutron-rich nuclei using the nuclear shell model employing the complex Berggren ensemble representing the bound single-particle states, unbound Gamow states, and the non-resonant continuum. In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body finite depth (Woods-Saxon) potential and a residual two-body interaction. We discuss the basic ingredients of the Gamow Shell Model. The formalism is illustrated by calculations involving {\it several} valence neutrons outside the double-magic core: $^{6-10}$He and $^{18-22}$O.

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arXiv2002

Gamow Shell Model Description of Neutron-Rich Nuclei

This work presents the first continuum shell-model study of weakly bound neutron-rich nuclei involving multiconfiguration mixing. For the single-particle basis, the complex-energy Berggren ensemble representing the bound single-particle states, narrow resonances, and the non-resonant continuum background is taken. Our shell-model Hamiltonian consists of a one-body finite potential and a zero-range residual two-body interaction. The systems with two valence neutrons are considered. The Gamow shell model, which is a straightforward extension of the traditional shell model, is shown to be an excellent tool for the microscopic description of weakly bound systems. It is demonstrated that the residual interaction coupling to the particle continuum is important; in some cases, it can give rise to the binding of a nucleus.

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arXiv2001

First-forbidden mirror beta-decays in A=17 mass region

The first-forbidden beta-decay of 17Ne into the 'halo' state J=1/2+ of 17F presents one of the largest measured asymmetries for mirror beta-decay feeding bound final states. This asymmetry is studied in the framework of the Shell Model Embedded in the Continuum (SMEC). The spatial extent of single particle orbits is constrained by the proton capture cross-section 16O(p,gamma)17F calculated in SMEC . This allows to estimate the mirror symmetry breaking in 17F/17O and 17Ne/17N nuclei.

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arXiv2001

Descritpion of Exotic Nuclei Using Continuum Shell Model

In weakly bound exotic nuclei, number of excited bound states or narrow resonances is small and, moreover, they couple strongly to the particle continuum. Hence, these systems should be described in the quantum open system formalism which does not artificially separate the subspaces of (quasi-) bound and scattering states. The Shell Model Embedded in the Continuum provides a novel approach which solves this problem. Examples of application in sd-shell nuclei will be presented.

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arXiv2000

Shell model description of 16O(p,gamma)17F and 16O(p,p)16O reactions

We present shell model calculations of both the structure of 17F and the reactions 16O(p,gamma)17F, 16O(p,p)16O. We use the ZBM interaction which provides a good description of the properties of 16O and neighbouring nuclei and, in particular it takes account for the complicated correlations in coexisting low-lying states of 16O.

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arXiv1999

Finite size effects and the order of a phase transition in fragmenting nuclear systems

We discuss the implications of finite size effects on the determination of the order of a phase transition which may occur in infinite systems. We introduce a specific model to which we apply different tests. They are aimed to characterise the smoothed transition observed in a finite system. We show that the microcanonical ensemble may be a useful framework for the determination of the nature of such transitions.

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