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Register a new userParity-violating polarization in $np to dgamma$ with a pionless effective field theory
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We consider the two-nucleon weak interaction with a pionless effective field theory. Dibaryon fields are introduced to facilitate calculations and ensure precision in the initial and final state propagators. Weak interactions are accounted for with the parity-violating dibaryon-nucleon-nucleon vertices, which contain unknown weak dibaryon-nucleon-nucleon coupling constants. We apply the model to the calculation of a parity-violating observable in the neutron-proton capture at threshold. Result is obtained up to the linear order in the unknown dibaryon-nucleon-nucleon coupling constants. We compare our result to the one obtained from a hybrid calculation, and discuss the extension to weak interactions in the few-body systems.
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We consider a pionless effective theory with dibaryon fields for the description of the weak process involving two nucleons. We construct leading order Lagrangians that contain nucleon-dibaryon weak coupling constants. We calculate the physical observable in the photodisintegration of the deuteron at threshold and obtain the result in terms of the nucleon-dibaryon weak coupling constants. Relation to existing calculations is discussed.
Nuclear parity violation is studied with polarized neutrons in the photodisintegration of the deuteron at low energies. A pionless effective field theory with di-baryon fields is used for the investigation. Hadronic weak interactions are treated by parity-violating di-baryon-nucleon-nucleon vertices, which have undetermined coupling contants. A parity-violating asymmetry in the process is calculated for the incident photon energy up to 30 MeV. If experimental data for the parity-violating asymmetry become available in the future, we will be able to determine the unknown coupling contants in the parity-violating vertices.
With the use of pionless effective field theory including dibaryon fields, we study the $gamma d to vec{n} p$ reaction for the laboratory photon energy $E_gamma^{lab}$ ranging from threshold to 30 MeV. Our main goal is to calculate the neutron polarization $P_{y}$ defined as $P_{y} = (sigma_+ - sigma_-)/(sigma_+ + sigma_-)$, where $sigma_+$ and $sigma_-$ are the differential cross sections for the spin-up and spin-down neutrons, respectively, along the axis perpendicular to the reaction plane. We also calculate the total cross section as well as the differential cross section $sigma(theta)$, where $theta$ is the colatitude angle. Although the results for the total and differential cross sections are found to agree reasonably well with the data, the results for $P_{y}$ show significant discrepancy with the experiment. We comment on this discrepancy.
We study breakup of the deuteron induced by neutrinos in the neutral $ u dto u np$, $bar{ u} dto bar{ u} np$ and the charged $bar{ u} dto e^+ n n$, $ u dto e^- pp$ processes. Pionless effective field theory with dibaryon fields is used to calculate the total cross sections for neutrino energies $E_ u$ from threshold to 20 MeV. Amplitudes are expanded up to next-to-leading order, and the partial wave is truncated at $P$-waves. The Coulomb interaction between two protons is included nonperturbatively in the reaction amplitudes, and an analytic expression of the amplitudes is obtained. The contribution of the next-to-leading order to the total cross section is in the range of 5.2$-$9.9% in magnitude, and that of the $P$-wave is 2.4$-$2.8% at $E_ u = 20$ MeV. Uncertainty arising from an axial isovector low-energy constant is estimated to be on the order of 1%.
A systematic description of low-energy observables in light nuclei is presented. The effective field theory formalism without pions is extended to: i) predictions with next-to-leading-order (non-perturbatively) accuracy for the 4-helium binding energy B({alpha}), the triton charge radius, and the 3-helium-neutron scattering length; ii) phase shifts for neutron-deuteron scattering and {alpha}-neutron low-energy scattering at leading order; iii) the ground states of the 5-helium (with and without Coulomb interaction) and 6-helium isotopes up to next-to-leading order; The convergence from leading- to next-to-leading order of the theory is demonstrated for correlations between: i) the triton binding energy B(t) and the triton charge radius; ii) B(t) and the 4-helium binding energy B({alpha}); Furthermore, a correlation between B(t) and the scattering length in the singlet S-wave channel of neutron-helium-3 scattering is discovered, and a model-independent estimate for the trinucleon binding energy splitting is provided. The results provide evidence for the usefulness of the applied power-counting scheme, treating next-to-leading-order interactions nonperturbatively and four-nucleon interactions as, at least, one order higher. The 5- and 6-helium ground states are analyzed with a power-counting scheme which includes the momentum-dependent next-to-leading order vertices perturbatively. All calculations include a full treatment of the Coulomb interaction. The assessment of numerical uncertainties associated with the solution of the few-body equation of motion through the Resonating Group Method parallels the report of the results for light nuclei in order to establish this method as practical for the analysis of systems with up to six particles interacting via short-range interactions.
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