https://doi.org/10.1140/epja/s10050-024-01340-4
Regular Article –Theoretical Physics
Ab initio description of monopole resonances in light- and medium-mass nuclei
I. Technical aspects and uncertainties of ab initio PGCM calculations
1
Technische Universität Darmstadt, Department of Physics, 64289, Darmstadt, Germany
2
ExtreMe Matter Institute EMMI, GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
3
IRFU, CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
4
KU Leuven, Department of Physics and Astronomy, Instituut voor Kern- en Stralingsfysica, 3001, Leuven, Belgium
5
CEA, DAM, DIF, 91297, Arpajon, France
6
Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, 91680, Bruyères-le-Châtel, France
7
CEA, DES, IRESNE, DER, SPRC, 13108, Saint-Paul-lès-Durance, France
8
Helmholtz Forschungsakademie Hessen für FAIR, GSI Helmholtzzentrum, 64289, Darmstadt, Germany
a
aporro@theorie.ikp.physik.tu-darmstadt.de
Received:
19
March
2024
Accepted:
16
May
2024
Published online:
19
June
2024
Giant resonances (GRs) are a striking manifestation of collective motions in mesoscopic systems such as atomic nuclei. Until recently, theoretical investigations have essentially relied on the (quasiparticle) random phase approximation ((Q)RPA), and extensions of it, based on phenomenological energy density functionals (EDFs). As part of a current effort to describe GRs within an ab initio theoretical scheme, the present work promotes the use of the projected generator coordinate method (PGCM). This method, which can handle anharmonic effects while satisfying symmetries of the nuclear Hamiltonian, displays a favorable (i.e. mean-field-like) scaling with system’s size. Presently focusing on the isoscalar giant monopole resonance (GMR) of light- and medium-mass nuclei, PGCM’s potential to deliver wide-range ab initio studies of GRs in closed- and open-shell nuclei encompassing pairing, deformation, and shape coexistence effects is demonstrated. The comparison with consistent QRPA calculations highlights PGCM’s unique attributes and sheds light on the intricate interplay of nuclear collective excitations. The present paper is the first in a series of four and focuses on technical aspects and uncertainty quantification of ab initio PGCM calculations of GMR using the doubly open-shell 
Ti as an illustrative example. The second paper displays results for a set of nuclei of physical interest and proceeds to the comparison with consistent (deformed) ab initio QRPA calculations. While the third paper analyzes useful moments of the monopolar strength function and different ways to access them within PGCM calculations, the fourth paper focuses on the effect of the symmetry restoration on the monopole strength function.
© The Author(s) 2024
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
