Renormalization of Chiral Effective Field Theory in the Nucleon-Nucleon Sector
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Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Thim, Oliver
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The calculation of nuclear properties from QCD, the underlying theory of the strong
nuclear force, is still an open problem in physics. Effective field theories provide a
possible solution by describing nuclei in terms of effective degrees of freedom; neutrons,
protons, and pions. The effective description comes at a cost, namely undetermined
parameters known as low-energy constants (LECs), that need to be fixed
by experimental data. Furthermore, while renormalization-group (RG) invariance
of predictions is a field-theoretic requirement, it is known that interaction potentials
constructed with Weinberg power counting (WPC) are not RG invariant at leading
order.
The purpose of this thesis is to study a leading order modified Weinberg power counting
potential, with additional counter terms and their associated LECs promoted
to leading order. We show that the modified potential gives RG invariant predictions
of nucleon-nucleon scattering phase shifts in partial waves that are otherwise
problematic in WPC. Moreover, Bayesian inference is used to determine LECs from
measured total scattering cross sections, which allows to account for both experimental
and model uncertainties. RG-invariant predictions of scattering cross sections
are demonstrated using the obtained posterior distributions of LECs. In conclusion,
we find that the modified potential performs better, producing RG-invariant results
for phase shifts and cross sections. We also show that total scattering cross sections
do not impose very hard constraints on all LECs which calls for the inclusion of
more experimental data in the inference.
Beskrivning
Ämne/nyckelord
nuclear physics , XEFT , renormalization , neutron-proton scattering , Bayesian inference , LECs , power counting , modified Weinberg power counting