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Register a new userParticle-unstable light nuclei with a Sturmian approach that preserves the Pauli principle
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Sturmian theory for nucleon-nucleus scattering is discussed in the presence of all the phenomenological ingredients necessary for the description of weakly-bound (or particle-unstable) light nuclear systems. Currently, we use a macroscopic potential model of collective nature. The analysis shows that the couplings to low-energy collective-core excitations are fundamental but they are physically meaningful only if the constraints introduced by the Pauli principle are taken into account. The formalism leads one to discuss a new concept, Pauli hindrance, which appears to be important to understand the structure of weakly-bound and unbound systems.
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The fundamental ingredients of the MCAS (multi-channel algebraic scattering) method are discussed. The main feature, namely the application of the sturmian theory for nucleon-nucleus scattering, allows solution of the scattering problem given the phenomenological ingredients necessary for the description of weakly-bound (or particle-unstable) light nuclear systems. Currently, to describe these systems, we use a macroscopic, collective model. Analyses show that the couplings to low-energy collective-core excitations are fundamental but they are physically meaningful only if the constraints introduced by the Pauli principle are taken into account. For this we introduce in the nucleon-nucleus system the Orthogonalizing Pseudo-Potential formalism, extended to collective excitations of the core. The formalism leads one to discuss a new concept, Pauli hindrance, which appears to be important especially to understand the structure of weakly-bound and unbound systems.
The physics of radioactive ion beams implies the description of weakly-bound nuclear systems. One key aspect concerns the coupling to low-lying collective-type excited states, which for these systems might not be stable levels, but particle emitting resonances. In this work we describe how the scattering cross section and compound spectra change when the colliding fragments have such collective excitations featuring particle emission. We explore this question in the framework of a multi-channel algebraic scattering method of determining nucleon-nucleus cross sections at low energies. For a range of light-mass, particle-unstable nuclear targets, scattering cross sections as well as the spectra of the compound nuclei formed have been determined from calculations that do and do not consider particle emission widths for nuclear states. Assuming a resonance character for target states markedly varies evaluated cross sections from those obtained assuming the target spectrum to have entirely discrete states.
A new development in the antisymmetrization of the first-order nucleon-nucleus elastic microscopic optical potential is presented which systematically includes the many-body character of the nucleus within the two-body scattering operators. The results reduce the overall strength of the nucleon-nucleus potential and require the inclusion of historically excluded channels from the nucleon-nucleon potential input. Calculations produced improve the match with neutron-nucleus total cross section, elastic proton-nucleus differential cross section, and spin observable data. A comparison is also done using different nucleon-nucleon potentials from the past twenty years.
We study effects of the Pauli principle on the potential energy of two-cluster systems. The object of the investigation is the lightest nuclei of p-shell with a dominant $alpha$-cluster channel. For this aim we construct matrix elements of two-cluster potential energy between cluster oscillator functions with and without full antisymmetrization. Eigenvalues and eigenfunctions of the potential energy matrix are studied in detail. Eigenfunctions of the potential energy operator are presented in oscillator, coordinate and momentum spaces. We demonstrate that the Pauli principle affects more strongly the eigenfunctions than the eigenvalues of the matrix and leads to the formation of resonance and trapped states.
We study the real-time evolution of an electron influenced by intense electromagnetic fields using the time-dependent basis light-front quantization (tBLFQ) framework. We focus on demonstrating the non-perturbative feature of the tBLFQ approach through a realistic application of the strong coupling QED problem, in which the electromagnetic fields are generated by an ultra-relativistic nucleus. We calculate transitions of an electron influenced by such electromagnetic fields and we show agreement with light-front perturbation theory when the atomic number of the nucleus is small. We compare tBLFQ simulations with perturbative calculations for nuclei with different atomic numbers, and obtain the significant higher-order contributions for heavy nuclei. The simulated real-time evolution of the momentum distribution of an electron evolving inside the strong electromagnetic fields exhibits significant non-perturbative corrections comparing to light-front perturbation theory calculations. The formalism used in this investigation can be extended to QCD problems in heavy ion collisions and electron ion collisions.
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