The data perspective on chiral effective field theory
Doktorsavhandling, 2017

The scientific method implies a dynamical relationship between experiment and theory. Indeed, experimental results are understood through theories, which themselves are of less value until confronted with experiment. In this thesis I study this relationship by quantifying two key properties of theories: theoretical uncertainties and predictive power. Specifically I investigate chiral effective field theory and the precision and accuracy by which it reproduces and predicts low-energy nuclear observables. I estimate both statistical and systematic uncertainties. The conclusion is that the latter, which in my approximation originates from omitted higher-order terms in the chiral expansion, are much larger than the former. In relation to this, I investigate the order-by-order convergence up to fourth order in the chiral expansion. I find that predictions generally improve with increasing order, while the additional low-energy constants (LECs) of the interaction makes it more difficult to fully constrain the theory. Furthermore, in order to accurately reproduce properties of heavier nuclei I see indications that it is necessary to include selected experimental data from such systems directly in the fitting of the interaction. In order to perform these studies I have developed accurate and efficient methods as well as computer codes for the calculation of observables. In particular, the application of automatic differentiation for derivative calculations is shown to be crucial for the minimization procedure. These developments open up new avenues for future studies. For example, it is now possible to do extensive sensitivity analyses of the experimental data and the model; to investigate the power counting from a data perspective; and incorporate more experimental data in the fitting procedure.

chiral EFT

few-nucleon physics

uncertainty quantification

two-nucleon scattering

nuclear physics

PJ-salen, Origo
Opponent: Senior researcher Dr. Michele Viviani, INFN, Pisa, Italien

Författare

Boris Karlsson

Chalmers, Fysik, Subatomär fysik och plasmafysik

Uncertainty Analysis and Order-by-Order Optimization of Chiral Nuclear Interactions

Physical Review X,; Vol. 6(2016)

Artikel i vetenskaplig tidskrift

Quantifying statistical uncertainties in ab initio nuclear physics using Lagrange multipliers

Physical Review C - Nuclear Physics,; Vol. 95(2017)p. 034002-

Artikel i vetenskaplig tidskrift

Statistical uncertainties of a chiral interaction at next-to-next-to leading order

Journal of Physics G: Nuclear and Particle Physics,; Vol. 42(2015)

Artikel i vetenskaplig tidskrift

B. D. Carlsson, A. Ekström, C. Forssén, Optimization of two- and three-nucleon interactions at N3LO in chiral EFT

One of the fundamental forces of nature is the strong force. Acting on extremely short distances it is responsible for keeping the protons and neutrons together in the atomic nucleus. Still, it is powerful enough to keep stars burning. Scientists have tried to understand this force for many decades, both with experiments and theoretical modelling. In this thesis I combine prior experimental and theoretical knowledge in a unique way to obtain an improved description of nuclear forces, with increased predictive power and known statistical and systematic uncertainties. This achievement provides an improved understanding of physics at the subatomic scale.

Ämneskategorier

Subatomär fysik

Fundament

Grundläggande vetenskaper

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

ISBN

978-91-7597-530-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4211

Utgivare

Chalmers tekniska högskola

PJ-salen, Origo

Opponent: Senior researcher Dr. Michele Viviani, INFN, Pisa, Italien