Dissertation/Thesis Abstract

Electroweak interactions and the delta resonance in a chiral effective field theory for nuclei
by Zhang, Xilin, Ph.D., Indiana University, 2012, 160; 3527657
Abstract (Summary)

In this thesis, we include the Delta (1232) resonance as manifest degrees of freedom and systematically study Electroweak interactions in the quantum hadrodynamics (QHD) effective field theory (EFT) which is constructed for the nuclear many-body problems. The motivations are twofold. Including the Delta is a key component in setting up the framework for studying the pion dynamics that connects the Lorentz symmetry, chiral symmetry (spontaneously broken), and nuclear properties. Moreover, the neutrino-oscillation experiments require a better understanding of neutrino-nucleus reactions. Their measurements (covering the resonance region) can provide valuable inputs for theoretical studies.

First, we show the EFT with spin-3/2 particles is self-consistent, and the so-called off shell interactions are redundant, which can be generalized to other high spin cases. In addition, Electroweak interactions are studied. The meson dominance mechanism is included to generate various currents' form factors (e.g. nucleon ↔ Delta transition currents). Then we proceed to calibrate the theory by studying the pion neutrinoproduction off nucleons. Various symmetries are explored for this process. The photon production is also investigated, motivated by the excess event puzzle in the MiniBooNE experiment. Two contact terms that are partially related to the proposed anomalous meson interactions are shown to contribute little in the photon production with neutrino energy below 0.5 GeV. To continue the quest, we calculate the (in)coherent productions from 12 C (major complex nuclei in the detector). The (in)coherent pion productions are also calculated and compared to the NUANCE event generator, which shows the importance of nonresonant diagrams. We see small contributions of the two mentioned contact terms in the incoherent photon production, but significant contributions in the coherent one. It seems unpromising for the two terms to triple the photon production to explain the excess events. However this study needs to be extrapolated to GeV region to achieve a firm conclusion, and will be shown elsewhere. The calculations are benchmarked by the inclusive electron-12C scattering and the coherent pion photoproduction. The Delta dynamics in the nuclei is explored. We find the Delta-meson interactions can generate its spin-orbit coupling that is consistent with one but not both phenomenological results.

Indexing (document details)
Advisor: Serot, Brian D., Liao, Jinfeng
Commitee: Horowitz, Charles J., Snow, William Michael, Szczepaniak, Adam
School: Indiana University
Department: Physics
School Location: United States -- Indiana
Source: DAI-B 74/02(E), Dissertation Abstracts International
Subjects: Physics, Theoretical physics, Nuclear physics
Keywords: Chiral effective field theory, Delta resonance, Electroweak interactions, Photon production, Pion production, Qhd
Publication Number: 3527657
ISBN: 978-1-267-62074-3
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