arXiv subjects

Linda Hlophe

Publications and source records attributed to Linda Hlophe.

6 recordsLinked to original sources

arXiv2024

Motivations for Early High-Profile FRIB Experiments

This white paper is the result of a collaboration by those that attended a workshop at the Facility for Rare Isotope Beams (FRIB), organized by the FRIB Theory Alliance (FRIB-TA), on Theoretical Justifications and Motivations for Early High-Profile FRIB Experiments. It covers a wide range of topics related to the science that will be explored at FRIB. After a brief introduction, the sections address: (II) Overview of theoretical methods, (III) Experimental capabilities, (IV) Structure, (V) Near-threshold Physics, (VI) Reaction mechanisms, (VII) Nuclear equations of state, (VIII) Nuclear astrophysics, (IX) Fundamental symmetries, and (X) Experimental design and uncertainty quantification.

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arXiv2022

Quantifying uncertainties due to irreducible three-body forces in deuteron-nucleus reactions

\noindent{\bf Background:} Deuteron-induced nuclear reactions are an essential tool for probing the structure of nuclei as well as astrophysical information such as $(n,γ)$ cross sections. The deuteron-nucleus system is typically described within a Faddeev three-body model consisting of a neutron ($n$), a proton ($p$), and the target nucleus ($A$) interacting through pairwise phenomenological potentials. While Faddeev techniques enable the exact description of the three-body dynamics, their predictive power is limited in part by the omission of irreducible neutron-proton-nucleus three-body force ($n$-$p$-$A$ 3BF). {\bf Results:} By comparing the Faddeev and NCSM/RGM results, we show that the irreducible $n$-$p$-$α$ 3BF has a non-negligible effect on bound state and scattering observables alike. Specifically, the Faddeev approach %are yields a $^6$Li ground state that is approximately $600$~keV shallower than the one obtained with the NCSM/RGM. Additionally, the Faddeev calculations for $d$+$α$ scattering yield a $3^+$ resonance that is located approximately $400$~keV higher in energy compared to the NCSM/RGM result. The shape of the $d$+$α$ angular distributions computed using the two approaches also differ, owing to the discrepancy in the predictions of the $3^+$ resonance energy.

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arXiv2020

From bound states to the continuum

This white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program "From bound states to the continuum: Connecting bound state calculations with scattering and reaction theory". One of the biggest and most important frontiers in nuclear theory today is to construct better and stronger bridges between bound state calculations and calculations in the continuum, especially scattering and reaction theory, as well as teasing out the influence of the continuum on states near threshold. This is particularly challenging as many-body structure calculations typically use a bound state basis, while reaction calculations more commonly utilize few-body continuum approaches. The many-body bound state and few-body continuum methods use different language and emphasize different properties. To build better foundations for these bridges, we present an overview of several bound state and continuum methods and, where possible, point to current and possible future connections.

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arXiv2020

Properties of a separable representation of optical potentials

Background: Separable interactions have a long history in nuclear physics. In the last few years, separable expansions have been used to represent the optical potential between a nucleon (proton or neutron) and a target. Purpose: We explore the non-local properties of these separable optical potentials as well as their convergence behavior. Method: For a couple of cases, we use the generalized Ersnt-Shakin-Thaler scheme to generate separable interactions starting from local optical potentials. We study the variation of the interaction with energy range and rank. Results: We find that, overall the off-diagonal behavior of the converged separable interaction deviates from the Gaussian form assumed by Perey and Buck. However, in the region surrounding the maximum depth the Gaussian form works quite well. Focusing on this region, we study potentials describing neutron elastic scattering on $^{16}$O and $^{48}$Ca for beam energies in the range of $ E=$10-50 MeV and explore several measures of non-locality of the separable interactions. Conclusions: When the energy range considered for generating the separable interaction is $0\le E_{range}\le 50$ MeV, the resulting non-locality is large and target dependent. Contrarily, the nonlocality obtained including larger energy ranges in the separable procedure is independent of the target and other details of the original local potential. We find that, even when including in the expansion many support points with energy ranges $0\le E_{range}\le 2400$ MeV, the resulting potential retains non-local behavior. Connections with microscopic optical potentials as well as other transformations used in the nucleon-nucleon domain are made.

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arXiv2016

Separable Representation of Multichannel Nucleon-Nucleus Optical Potentials

One important ingredient for many applications of nuclear physics to astrophysics, nuclear energy, and stockpile stewardship are cross sections for reactions of neutrons with rare isotopes. Since direct measurements are often not feasible, indirect methods, e.g. (d,p) reactions, should be used. Those (d,p) reactions may be viewed as three-body reactions and described with Faddeev techniques. Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. Optical potentials representing the effective interactions in the neutron (proton) nucleus subsystem are usually non-Hermitian as well as energy-dependent. Including excitations of the nucleus in the calculation requires a multichannel optical potential. The purpose of this paper is to introduce a separable, energy-dependent multichannel representation of complex, energy-dependent optical potentials that contain excitations of the nucleus and that fulfill reciprocity exactly. Momentum space Lippmann-Schwinger integral equations are solved with standard techniques to obtain the form factors for the separable representation. Starting from energy-dependent multichannel optical potentials for neutron and proton scattering from $^{12}$C, separable representations based on a generalization of the Ernst-Shakin-Thaler (EST) scheme are constructed which fulfill reciprocity exactly. Applications to n$+^{12}$C and p$+^{12}$C scattering are investigated for energies from 0 to 50~MeV.

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arXiv2015

Separable Representation of Energy-Dependent Optical Potentials

Background. One important ingredient for many applications of nuclear physics to astrophysics, nuclear energy, and stockpile stewardship are cross sections for reactions of neutrons with rare isotopes. Since direct measurements are often not feasible, indirect methods, e.g. (d,p) reactions, should be used. Those (d,p) reactions may be viewed as three-body reactions and described with Faddeev techniques. Purpose. Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. Optical potentials representing the effective interactions in the neutron (proton) nucleus subsystem are usually non-Hermitian as well as energy-dependent. Potential matrix elements as well as transition matrix elements calculated with them must fulfill the reciprocity theorem. The purpose of this paper is to introduce a separable, energy-dependent representation of complex, energy-dependent optical potentials that fulfill reciprocity exactly. Results. Starting from a separable, energy-independent representation of global optical potentials based on a generalization of the Ernst-Shakin-Thaler (EST) scheme, a further generalization is needed to take into account the energy dependence. Applications to n$+^{48}$Ca, n$+^{208}$Pb, and p$+^{208}$Pb are investigated for energies from 0 to 50~MeV with special emphasis on fulfilling reciprocity. Conclusions. We find that the energy-dependent separable representation of complex, energy-dependent phenomenological optical potentials fulfills reciprocity exactly. In addition, taking into account the explicit energy dependence slightly improves the description of the $S$ matrix elements.

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