Efficient sampling of Bayesian posteriors and predictive distributions in χEFT
Licentiatavhandling, 2021

In this thesis I employ Bayesian statistics to quantify parametric and epistemic uncertainties in chiral effective field theories (χEFT) and propagate these forward to predictions of observables in low-energy nuclear physics. Two primary sources of uncertainty---experimental errors and the theoretical error induced by the truncation of the EFT at up to next-to-next-to-leading-order---are modelled and accounted for in the posterior distributions of the unknown low-energy constants (LECs) that govern interaction strengths in χEFT. These posteriors are computationally challenging to extract and I therefore introduce an advanced Markov chain Monte Carlo (MCMC) algorithm, known as Hamiltonian Monte Carlo, and investigate its performance. I compare its sampling efficiency to standard MCMC algorithms and find reductions in computation time by factors around 3-6 in the present work. I exploit the extracted posteriors to produce predictive distributions for neutron-proton and proton-proton scattering cross sections below and above the pion production threshold and check the consistency of the model predictions against empirical data and higher-order point estimates. I find that the predictive distributions provide reliable credibility intervals as long as the size of the truncation error is estimated from expansion coefficients at next-to-leading-order and above. The LEC posteriors are also central to uncertainty quantification in few- and manybody systems, and as part of a larger collaboration I explore constraints on three-nucleon forces imposed by light-nuclei observables.

nuclear physics

Bayesian parameter estimation

two-nucleon scattering

chiral effective field theory

Markov chain Monte Carlo

Opponent: Arnau Rios Huguet, University of Surrey, Storbritannien


Isak Svensson

Subatomär, högenergi- och plasmafysik DP

S. Wesolowski, I. Svensson, A. Ekström, C. Forssén, R.J. Furnstahl, J. A. Melendez, and D. R. Phillips. Fast and rigorous constraints on chiral three-nucleon forces from few-body observables

I. Svensson, A. Ekström, and C. Forssén. Bayesian parameter estimation in χEFT using Hamiltonian Monte Carlo

Strong interactions for precision nuclear physics (PrecisionNuclei)

Europeiska kommissionen (EU) (EC/H2020/758027), 2018-02-01 -- 2023-01-31.


Subatomär fysik


Grundläggande vetenskaper


C3SE (Chalmers Centre for Computational Science and Engineering)





Opponent: Arnau Rios Huguet, University of Surrey, Storbritannien

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