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F. Sammarruca

Publications and source records attributed to F. Sammarruca.

32 records · Page 2Linked to original sources
arXiv2007

In-Medium Hadronic Interactions and the Nuclear Equation of State

Microscopic studies of nuclear matter under diverse conditions of density and asymmetry are of great contemporary interest. Concerning terrestrial applications, they relate to future experimental facilities that will make it possible to study systems with extreme neutron-to-proton ratio. In this talk, I will review recent efforts of my group aimed at exploring nuclear interactions in the medium through the nuclear equation of state (EoS). The approach we take is microscopic and relativistic, with the predicted EoS properties derived from realistic nucleon-nucleon potentials. I will also discuss work in progress. Most recently, we completed a DBHF calculation of the $Λ$ hyperon binding energy in nuclear matter.

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arXiv2007

Spin polarized neutron matter within the Dirac-Brueckner-Hartree-Fock approach

The relation between energy and density (known as the nuclear equation of state) plays a major role in a variety of nuclear and astrophysical systems. Spin and isospin asymmetries can have a dramatic impact on the equation of state and possibly alter its stability conditions. An example is the possible manifestation of ferromagnetic instabilities, which would indicate the existence, at a certain density, of a spin-polarized state with lower energy than the unpolarized one. This issue is being discussed extensively in the literature and the conclusions are presently very model dependent. We will report and discuss our recent progress in the study of spin-polarized neutron matter. The approach we take is microscopic and relativistic. The calculated neutron matter properties are derived from realistic nucleon-nucleon interactions. This makes it possible to understand the nature of the EOS properties in terms of specific features of the nuclear force model.

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arXiv2005

Nucleon-nucleon cross sections in neutron-rich matter

We calculate nucleon-nucleon cross sections in the nuclear medium with unequal densities of protons and neutrons. We use the Dirac-Brueckner-Hartree-Fock approach together with realistic nucleon-nucleon potentials. We examine the effect of neutron/proton asymmetry and find that, although generally mild, it can be significant in specific regions of the phase space under consideration.

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arXiv2004

Inclusion of non-spherical components of the Pauli blocking operator in (p,p') reactions

We present the first calculations of proton elastic and inelastic scattering in which the Pauli blocking operator contains the leading non-spherical components as well as the usual spherical (angle-averaged) part. We develop a formalism for including the contributions to the effective nucleon-nucleon interaction from the resulting new G-matrix elements that extend the usual two-nucleon spin structure and may not conserve angular momentum. We explore the consequences of parity conservation, time reversal invariance, and nucleon-nucleon antisymmetrization for the new effective interaction. Changes to the calculated cross section and spin observables are small in the energy range from 100 to 200 MeV.

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arXiv2004

Predicting the single-proton/neutron potentials in asymmetric nuclear matter

We discuss the one-body potentials for protons and neutrons obtained from Dirac-Brueckner-Hartree-Fock calculations of neutron-rich matter, in particular their dependence upon the degree of proton/neutron asymmetry. The closely related symmetry potential is compared with empirical information from the isovector component of the nuclear optical potential.

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arXiv2004

Comment on "Unmasking the nuclear equation of state"

Referring to a recently published paper [J. Piekarewicz, Phys. Rev. C 69, 041301 (2004)], we point out that Dirac-Brueckner-Hartree-Fock calculations of the symmetry energy predict values of the neutron skin of heavy nuclei which are remarkably consistent with those from a recent ``best-fit'' analysis.

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arXiv2003

Exact treatment of Pauli exclusion effects in (p,p') reactions

This paper presents the first calculations of proton inelastic scattering in which the medium effect of Pauli blocking is included through an exact, rather than angle averaged, operator. This improvement is important in the isoscalar channel at proton energies near 100 MeV and fades as the energy rises. However, processes that emphasize finite-range exchange (such as $0^+\to 0^-$ reactions) still see significant effects at 200 MeV. The results depend on the directions of the incident and struck nucleon momenta that produce the most important contributions to the DWBA integral at each scattering angle.

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arXiv2003

Microscopic calculations in asymmetric nuclear matter

A microscopic calculation of the equation of state for asymmetric nuclear matter is presented. We employ realistic nucleon-nucleon forces and operate within the Dirac-Brueckner-Hartree-Fock approach to nuclear matter. The focal point of this paper is a (momentum-space) G-matrix which properly accounts for the asymmetry between protons and neutrons. This will merge naturally into the development of an effective interaction suitable for applications to asymmetric nuclei, which will be the object of extensive study in the future.

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arXiv2001

Comparison between chiral and meson-theoretic nucleon-nucleon potentials through (p,p') reactions

We use proton-nucleus reaction data at intermediate energies to test the emerging new generation of chiral nucleon-nucleon (NN) potentials. Predictions from a high quality one-boson-exchange (OBE) force are used for comparison and evaluation. Both the chiral and OBE models fit NN phase shifts accurately, and the differences between the two forces for proton-induced reactions are small. A comparison to a chiral model with a less accurate NN description sets the scale for the ability of such models to work for nuclear reactions.

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arXiv1999

Microscopic calculations of medium effects for 200-MeV (p,p') reactions

We examine the quality of a G-matrix calculation of the effective nucleon-nucleon (NN) interaction for the prediction of the cross section and analyzing power for 200-MeV (p,p') reactions that populate natural parity states in $^{16}$O, $^{28}$Si, and $^{40}$Ca. This calculation is based on a one-boson-exchange model of the free NN force that reproduces NN observables well. The G-matrix includes the effects of Pauli blocking, nuclear binding, and strong relativistic mean-field potentials. The implications of adjustments to the effective mass ansatz to improve the quality of the approximation at momenta above the Fermi level will be discussed, along with the general quality of agreement to a variety of (p,p') transitions.

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arXiv1996

Triton Binding Energy and Minimal Relativity

For relativistic three-body calculations, essentially two different approaches are in use: field theory and relativistic direct interactions. Results for relativistic corrections of the triton binding energy obtained from the two approaches differ even in their sign, which is rather puzzling. In this paper, we discuss the origin of such discrepancy. We show that the use of an invariant two-body amplitude, as done in the field-theoretic approach, increases the triton binding energy by about 0.30 MeV. This may explain a large part of the discrepancy.

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arXiv1995

The Non-Local Nature of the Nuclear Force and its Impact on Nuclear Structure

We calculate the triton binding energy with a non-local NN potential that fits the world NN data below 350 MeV with the almost perfect $χ^2$/datum of 1.03. The non-locality is derived from relativistic meson field theory. The result obtained in a 34-channel, charge-dependent Faddeev calculation is 8.00 MeV, which is 0.4 MeV above the predictions by local NN potentials. The increase in binding energy can be clearly attributed to the off-shell behavior of the non-local potential. Our result cuts in half the discrepancy between theory and experiment established from local NN potentials. Implications for other areas of microscopic nuclear structure, in which underbinding is a traditional problem, are discussed.

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arXiv1992

Relativistic Corrections to the Triton Binding Energy

The influence of relativity on the triton binding energy is investigated. The relativistic three-dimensional version of the Bethe-Salpeter equation proposed by Blankenbecler and Sugar (BbS) is used. Relativistic (non-separable) one-boson-exchange potentials (constructed in the BbS framework) are employed for the two-nucleon interaction. In a 34-channel Faddeev calculation, it is found that relativistic effects increase the triton binding energy by about 0.2 MeV. Including charge-dependence (besides relativity), the final triton binding energy predictions are 8.33 and 8.16 MeV for the Bonn A and B potential, respectively.

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