JupiterNCSM: A Pantheon of Nuclear Physics —an implementation of three-nucleon forces in the no-core shell model—
Doktorsavhandling, 2021

It is well established that three-nucleon forces (3NFs) are necessary for achieving
realistic and accurate descriptions of atomic nuclei. In particular, such forces arise
naturally when using chiral effective field theories (χEFT). However, due to the
huge computational complexity associated with the inclusion of 3NFs in many-body
methods they are often approximated or neglected completely. In this thesis, three
different methods to include the physics of 3NFs in the ab initio no-core shell-model
(NCSM) have been implemented and tested. In the first method, we approximate
the 3NFs as effective two-body operators by exploiting Wick’s theorem to normal
order the 3NF relative a harmonic-oscillator Slater determinant reference state and
discarding the remaining three-body term. We explored the performance of this
single-reference normal-ordered two-body approximation on the ground-state ener-
gies of the two smallest closed-core nuclei, 4He and 16O, in particular focusing on
consequences of the breaking of translational symmetry. The second approach is a
full implementation of 3NFs in a new NCSM code, named JupiterNCSM, that we
provide as an open-source research software. We have validated and benchmarked
JupiterNCSM against other codes and we have specifically used it to investigate the
effects of different 3NFs on light p-shell nuclei 6He and 6Li. Finally, we implement
the eigenvector continuation (EVC) method to emulate the response of ground-state
energies of the aforementioned A = 6 nuclei to variations in the low-energy constants
of χEFT that parametrize the 3NFs. In this approach, the full Hamiltonian is pro-
jected onto a small subspace that is constructed from a few selected eigenvectors.
These training vectors are computed with JupiterNCSM in a large model space for
a small set of parameter values. This thesis provides the first EVC-based emulation
of nuclei computed with a Slater-determinant basis. After the training phase, we
find that EVC predictions offer a very high accuracy and more than seven orders
of magnitude computational speedup. As a result we are able to perform rigorous
statistical inferences to explore the effects of 3NFs in nuclear many-body systems.

PJ Salen, Fysikgården 2, and online via zoom (password: 296211)
Opponent: Dr. Kristina Launey, Department of Physics & Astronomy, Lousiana State University

Författare

Tor Djärv

Subatomär, högenergi- och plasmafysik DP

Denna avhandling handlar om hur trenukleonkrafter (3NK) kan tas med i strukturberäkningar för

atomkärnor på tre olika sätt. Det första sättet är exakt implementering av 3NK i den så kallade

No-Core-Shell-Model, vilket har resulterat i ett ny öppen-källkod program vid namn JupiterNCSM. Det andra sättet bygger på att approximera 3NK med effektiva tvånukleonkrafter via normalordning relativt ett harmoniskoscillatorkvanttillstånd. Slutligen det tredje sättet bygger på att konstruera en

emulator av önskade kärnfysikobservabler med hjälp av en relativt ny metod vid namn eigenvector continuation.

Ämneskategorier

Fysik

Fundament

Grundläggande vetenskaper

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

ISBN

978-91-7905-552-3

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5019

Utgivare

Chalmers tekniska högskola

PJ Salen, Fysikgården 2, and online via zoom (password: 296211)

Online

Opponent: Dr. Kristina Launey, Department of Physics & Astronomy, Lousiana State University

Mer information

Senast uppdaterat

2021-09-15