arXiv subjects

Nathalie Pillet

Publications and source records attributed to Nathalie Pillet.

8 recordsLinked to original sources

arXiv2026

Gogny interaction from beginnings to current challenges

In the present review, various facets of the phenomenological effective Gogny interaction, which was originally proposed in the 70's, are gathered for the first time in the same place. This involves both nuclear phenomena of interest that led to its creation and evolution as well as highly technical aspects that led the objectives to be achieved. With this in mind, a discussion structured around four key points is proposed. After a general introduction, the history and philosophy of the Gogny interaction is exposed. In particular, one highlights the way followed by D. Gogny to guide the determination of the parameters of its phenomenological interaction with results obtained from a realistic interaction using Hartree-Fock calculations and second order corrections and a G-matrix. One also shows how physical phenomena such as pairing or fission were essential to improve the initial parameterization. The evolution of the original analytical form over the years is then discussed. The second key point concern the emulator that was used for the generation of parameterizations. Its modifications, consistent with the evolution of its analytical form along the decades, are detailed. Other fitting procedures from other groups, more recent, are also evoked. The third key point is dedicated to the role of some nuclear matter properties in the fitting process and the acceptance of a parameterization. The objective of the last key point consists in highlighting some results obtained with the Gogny interaction in various domains such as nuclear structure, fission, reactions and nuclear data that have allowed to interpret many experimental data. Perpsectives are given explaining some paths that will be followed in the future concerning the functional itself as well as N-body approaches.

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arXiv2026

Mean-field proton-neutron pairing correlations with the Gogny D1S energy density functional

We study proton-neutron pairing correlations within the Hartree-Fock-Bogoliubov (HFB) framework using Gogny-type energy density functionals. By allowing for proton-neutron mixing in the quasi-particle transformation, both isovector ($T=1$) and isoscalar ($T=0$) pairing channels are explicitly included at the mean-field level. The \texttt{TAURUS} code has been extended to treat density-dependent Gogny interactions in this generalized HFB scheme. We examine the numerical behavior of the widely used Gogny D1S functional and compare it with calculations performed using the Hamiltonian-based Brink-Boecker B1 interaction supplemented by a zero-range spin-orbit term. When proton-neutron mixing is included and large single-particle spaces are employed, instabilities are observed for Gogny D1S due to the zero-range density-dependent term contribution to the proton-neutron pairing field, whereas stable solutions are obtained with the B1 interaction. Constrained HFB calculations performed in reduced configuration spaces allow us to explore total energy curves as functions of proton-neutron pairing collective coordinates in selected $sd$-shell nuclei. In all cases studied, the self-consistent minima correspond to vanishing proton-neutron pairing, with energy increasing rapidly as proton-neutron pairing correlations are introduced. These results provide insight into the behavior of Gogny functionals under generalized HFB conditions and offer useful guidance for future developments.

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arXiv2026

Probability distribution of observables from a Bogoliubov vacuum projected onto good particle number: application to scission configurations of an actinide

Nuclear fission dynamics described within nuclear energy density functional frameworks (EDF) have seen substantial advances in the last decade. Part of this success stems from projection techniques, which allow the computation f probability distribution functions (pdf) for selected observables such as particle number and angular momentum of the fragments. Predicting the pdf of other observables, such as the total kinetic energy of the fragments, remains undone. This work proposes a method to determine the complete pdf of a new category of observables from a Bogoliubov vacuum projected onto good particle number. It relies on sampling nucleonic configurations in coordinate and intrinsic-spin representation. We assess the feasibility and convergence properties of the method and apply it to states representative of the scission of an actinide. Fluctuations in fragment shapes, inter-fragment Coulomb and nuclear interaction as well as the corresponding torques are analyzed. We find that a significant fraction of the fluctuation of several measured fission observables is already present within the mean-field picture.

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arXiv2024

Construction of continuous collective energy landscapes for large amplitude nuclear many-body problems

Several protocols are proposed to build continuous energy surfaces of many-body quantum systems, regarding both energy and states. The standard variational principle is augmented with constraints on state overlap, ensuring arbitrary precision on continuity. As an illustration, the lowest energy and excited state paths relevant for the $^{240}$Pu asymmetric fission are studied. The scission is clearly signed, with a neutron excess in the neck, the ultimate glue before its rupture. Our approach can potentially connect any couple of Hilbert space states, which opens up new horizons for various applications.

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arXiv2021

Entanglement Rearrangement in Self-Consistent Nuclear Structure Calculations

Entanglement properties of $^4$He and $^6$He are investigated using nuclear many-body calculations, specifically the single-nucleon entanglement entropy, and the two-nucleon mutual information and negativity. Nuclear wavefunctions are obtained by performing active-space no-core configuration-interaction calculations using a two-body nucleon-nucleon interaction derived from chiral effective field theory. Entanglement measures within single-particle bases, the harmonic oscillator (HO), Hartree-Fock (HF), natural (NAT) and variational natural (VNAT) bases, are found to exhibit different degrees of complexity. Entanglement in both nuclei is found to be more localized within NAT and VNAT bases than within a HO basis for the optimal HO parameters, and, as anticipated, a core-valence (tensor product) structure emerges from the full six-body calculation of $^{6}$He. The two-nucleon mutual information shows that the VNAT basis, which typically exhibits good convergence properties, effectively decouples the active and inactive spaces. We conclude that measures of one- and two-nucleon entanglement are useful in analyzing the structure of nuclear wave functions, in particular the efficacy of basis states, and may provide useful metrics toward developing more efficient schemes for ab initio computations of the structure and reactions of nuclei, and quantum many-body systems more generally.

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arXiv2020

Future of Nuclear Fission Theory

There has been much recent interest in nuclear fission, due in part to a new appreciation of its relevance to astrophysics, stability of superheavy elements, and fundamental theory of neutrino interactions. At the same time, there have been important developments on a conceptual and computational level for the theory. The promising new theoretical avenues were the subject of a workshop held at the University of York in October 2019; this report summarises its findings and recommendations.

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arXiv2020

Description of the asymmetric to symmetric fission transition in the neutron-deficient Thoriums -- Role of the tensor force

In the present study, we have investigated the impact of the tensor force on fission paths, in particular the symmetric and asymmetric barriers in 230 Th, 226 Th, 222 Th and 216 Th isotopes which display an asymmetric to symmetric fission transition. This analysis has been performed within the HFB approach with (Q 20 ,Q 30 ,Q 40 ) as collective variable constraints, using the D1ST2a Gogny+tensor term interaction and comparing to the standard D1S Gogny interaction results. The effects from the tensor term on the potential energy surface landscape, and especially on barrier heights and its topology by opening a new valley in agreement with experimental data, are found to be crucial in the description of exotic actinide fission. We conclude that a tensor term should be integrated to the long range part of the effective interaction for a better description of the fission.

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arXiv2010

Particle-particle random phase approximation applied to Beryllium isotopes

This work is dedicated to the study of even-even 8-14 Be isotopes using the particle-particle Random Phase Approximation that accounts for two-body correlations in the core nucleus. A better description of energies and two-particle amplitudes is obtained in comparison with models assuming a neutron closed-shell (or subshell) core. A Wood-Saxon potential corrected by a phenomenological particle-vibration coupling term has been used for the neutron-core interaction and the D1S Gogny force for the neutron-neutron interaction. Calculated ground state properties as well as excited state ones are discussed and compared to experimental data. In particular, results suggest the same 2s_1/2-1p_1/2 shell inversion in 13Be as in 11Be.

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