Effective Field Theories and Electromagnetic Properties of Light Nuclei
Electromagnetic properties and nuclear reactions in light nuclei are investigated in different low-energy ranges applying effective field theories. In particular, two topics with distinct degrees of freedom are considered: one-neutron halo nuclei in the Halo effective field theory (Halo EFT) and thr...
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| Format: | Others |
| Language: | en |
| Published: |
2019
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| Online Access: | http://tuprints.ulb.tu-darmstadt.de/8682/1/Dissertation_genehmigt.pdf Braun, Jonas <http://tuprints.ulb.tu-darmstadt.de/view/person/Braun=3AJonas=3A=3A.html> : Effective Field Theories and Electromagnetic Properties of Light Nuclei. Technische Universität, Darmstadt [Ph.D. Thesis], (2019) |
| Summary: | Electromagnetic properties and nuclear reactions in light nuclei are investigated in different low-energy ranges applying effective field theories. In particular, two topics with distinct degrees of freedom are considered: one-neutron halo nuclei in the Halo effective field theory (Halo EFT) and threshold neutral pion photoproduction employing chiral effective field theory (χEFT).
In Halo EFT, the relevant degrees of freedom are the shallowly bound halo neutron and the tightly bound core nucleus. We extend the Halo EFT approach to shallow D-wave bound states, where the strong interaction between the core and the halo neutron is parametrized by contact interactions. We develop a power-counting scenario for arbitrary partial wave bound states and discuss its implications for universality. Furthermore, the results for electromagnetic form factors, electromagnetic transitions, and neutron capture reactions in weakly-bound D-wave states are presented of which we derive several universal correlations between electric observables. We apply our results to the two carbon isotopes C-15 and C-17, that both have shallow bound states with a neutron in a D-wave relative to the core.
Together with ab initio results from the no-core shell model (NCSM) and experimental data for the neutron separation energies, we obtain predictions for several electric observables in C-15 at leading order (LO), i.e. the quadrupole and hexadecupole moments and radii as well as E1 neutron capture cross sections, using the experimentally measured E2 transition strength in C-15. The effects of next-to-leading order corrections for our results are also addressed. We find that additional counterterms, which are required for the absorption of divergences, become more dominant in higher partial wave bound states, especially in the magnetic sector. Hence, we discuss the consequences for universality in such weakly-bound states.
Threshold neutral pion photoproduction off light nuclei is investigated in chiral perturbation theory (ChPT) at LO in the chiral expansion. We calculate the expectation value of the pion production operator with nuclear wave functions obtained by the NCSM and apply a density matrix approach for the evaluation of the appropriate pion production amplitudes. At LO, one-nucleon and two-nucleon effects contribute to the amplitude. We compare our results for H-2, H-3, and He-3 with the literature and find that we agree on both the one-nucleon contribution and the two-nucleon contribution, with the latter dominating at this order. The total amplitude is furthermore compared to experimental data of H-2 which reveals that the experimental result is about 11 % larger than our prediction. Moreover, we predict the threshold neutral pion photoproduction amplitude for Li-6 in ChPT for the first time. |
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