arXiv subjects

Francesca Sammarruca

Publications and source records attributed to Francesca Sammarruca.

At least 19 recordsLinked to original sources

arXiv2026

Analysis of the strengths of the contact potential at N4LO through nuclear and neutron matter

We examine the contact three-nucleon force at N4LO expressed as a density dependent potential. In Ref. [1], the necessary couplings (13, including two that appear in the leading three-nucleon force), were extracted from nd scattering observables. The contact strengths obtained through the three- nucleon continuum, without fi?ts to the triton, seem incompatible with the energy of nuclear and neutron matter. We take the opportunity to revisit the role of the cD, cE couplings of the leading three-nucleon force in nuclear matter and nuclei.

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arXiv2025

Tidal deformability in neutron stars from a microscopic point of view

We present results for the tidal deformability in neutron stars, the tidal Love number $k_2$, and the effective deformability of a binary system. The microscopic equation of state for cold $\beta$-stable neutron matter is based upon high-precision two-neutron forces and includes the chiral three-neutron forces required at the chosen order. We review and motivate our choices for the high-density continuation of the microscopic equation of state. We discuss our predictions and observe that they are well within multimessenger constraints. In contrast, stiff equations of state that yield radii larger than about 13 km are ruled out by GW170817 constraints.

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arXiv2024

General features of the stellar matter equation of state from microscopic theory, new maximum-mass constraints, and causality

The profile of a neutron star probes a very large range of densities, from the density of iron up to several times the density of saturated nuclear matter, and thus no theory of hadrons can be considered reliable if extended to those regions. We emphasize the importance of taking contemporary ab initio theories of nuclear and neutron matter as the baseline for any extension method, which will unavoidably involve some degree of phenomenology. We discuss how microscopic theory, on the one end, with causality and maximum-mass constraints, on the other, set strong boundaries to the high-density equation of state. We present our latest neutron star predictions where we combine polytropic extensions and parametrizations guided by speed of sound considerations. The predictions we show include our baseline neutron star cooling curves.

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arXiv2024

Recent advances in chiral EFT based nuclear forces and their applications

During the past two decades, chiral effective field theory has evolved into a powerful tool to derive nuclear forces from first principles. Nearly all two-nucleon interactions have been worked out up to sixth order of chiral perturbation theory, while, with few exceptions, three-nucleon forces, which play a subtle, but crucial role in microscopic nuclear structure calculations, have been derived up to fifth order. We review the current status of these forces as well as their applications in nuclear many-body systems. While the ab initio description of light nuclei is generally very successful, we point out and analyze problems encountered with medium-mass nuclei. We also survey the construction of equations of state for symmetric nuclear matter and neutron-rich matter based on chiral forces. A focal point is the symmetry energy and its impact on neutron skins and systems of astrophysical relevance. The physics of neutron-rich systems, from nuclei to compact stars, is essentially determined by the density dependence of the symmetry energy. We review the status of predictions in comparison with latest empirical constraints, with particular attention to those extracted from parity violating electron scattering.

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arXiv2023

The neutron skin of 48Ca and 208Pb: a critical analysis

We discuss the neutron skins of 48Ca and 208Pb. We review and critically examine modern predictions and empirical constraints, with special attention to the different interpretations of the findings from the PREX-II experiment and the recently reported value of the neutron skin in 48Ca extracted from the CREX experiment. We argue that, in the spirit of the ab initio philosophy, the path to understanding the behavior of dense neutron-rich matter must not circumvent fundamental nuclear forces. Based only on that argument, a thick neutron skin in 208Pb is highly unlikely.

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arXiv2023

Neutron matter: The unitary limit and its far-reaching impact

We explore low-density neutron matter and its behavior in proximity to the unitary limit. To that end, we construct unitary nucleon-nucleon potentials with infinite 1S0 neutron-neutron scattering lengths. We discuss the Berstch parameter in relation to results from ultra-cold atomic gases. Unitarity as a constraint for neutron matter and the symmetry energy has been discussed in the literature. We revisit some of those arguments and emphasize the relevance of keeping a firm link with low-energy nuclear physics for robust predictions of neutron-rich systems. Our predictions are obtained from realistic few-nucleon forces based on chiral effective field theory at N3LO.

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arXiv2022

The Symmetry Energy: Current Status of Ab Initio Predictions vs. Empirical Constraints

Infinite nuclear matter is a suitable laboratory to learn about nuclear forces in many-body systems. Modern theoretical predictions of neutron-rich matter are particularly timely in view of recent and planned measurements of observables which are sensitive to the equation of state of isospin-asymmetric matter. For these reasons, over the past several years we have taken a broad look at the equation of state of neutron-rich matter and the closely related symmetry energy, which is the focal point of this article. Its density dependence is of paramount importance for a number of nuclear and astrophysical systems, ranging from neutron skins to the structure of neutron stars. We review and discuss ab initio predictions in relation to recent empirical constraints. We emphasize and demonstrate that free-space NN data pose stringent constraints on the density dependence of the neutron matter equation of state, which essentially determines the slope of the symmetry energy at saturation.

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arXiv2022

Neutron skin systematics from microscopic equations of state

This paper presents an analysis of neutron skins based on fully microscopic equations of state, including chiral two- and three-nucleon forces consistently at N3LO. Other theoretical predictions and recent constraints are also addressed, such as those from the PREX II experiment and the latest parity-violating electron scattering measurement of the 27Al neutron skin.

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arXiv2022

The Equation of State of Neutron-Rich Matter at Fourth Order of Chiral Effective Field Theory and the Radius of a Medium-Mass Neutron Star

We report neutron star predictions based on our most recent equations of state. These are derived from chiral effective field theory, which allows for a systematic development of nuclear forces, order by order. We utilize high-quality two-nucleon interactions and include all three-nucleon forces up to fourth order in the chiral expansion. Our ab initio predictions are restricted to the domain of applicability of chiral effective field theory. However, stellar matter in the interior of neutron stars can be up to several times denser than normal nuclear matter at saturation, and its composition is essentially unknown. Following established practices, we extend our microscopic predictions to higher densities matching piecewise polytropes. The radius of the average-size neutron star, about 1.4 solar masses, is sensitive to the pressure at normal densities, and thus it is suitable to constrain ab initio theories of the equation of state. For this reason, we focus on the radius of medium-mass stars. We compare our results with other theoretical predictions and recent constraints.

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arXiv2021

An overview of symmetric nuclear matter properties from chiral interactions up to fourth order of the chiral expansion

We present and discuss predictions for a cross section of bulk and single-particle properties in symmetric nuclear matter based on recent high-quality nucleon-nucleon potentials at N3LO and including all subleading three-nucleon forces. We begin with the equation of state and its saturation properties and proceed to the single-nucleon potential. We also explore short-range correlations as seen through the defect function. The various predictions which we present have a common foundation in an internally consistent ab initio approach.

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arXiv2021

Analysis of the neutron matter equation of state and the symmetry energy up to fourth order of chiral effective field theory

We present predictions for the neutron matter equation of state, from leading to fourth order of chiral effective field theory, using recently developed, accurate chiral nucleon-nucleon potentials. We find the impact of subleading three-neutron forces to be mild and attractive. We also show order-by-order predictions for the symmetry energy, and discuss its density dependence in relation to empirical constraints.

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arXiv2020

Single-nucleon properties and pair correlations in nuclear matter from chiral two- and three-nucleon forces

We investigate single-particle properties in infinite nuclear matter using a variety of interactions. One of the focal points is to study the impact of chiral three-nucleon forces on the nucleon self-energy and related quantities, such as spectral function and momentum distribution. We also present results for pairing correlations in nuclear matter. We find characteristic and systematic differences between the predictions obtained with the (softer) chiral interactions and those based on one-boson-exchange or phenomenology.

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arXiv2020

Exploring the relationship between nuclear matter and finite nuclei with chiral two- and three-nucleon forces

We address the connection between the saturating behavior of infinite nuclear matter and the description of finite nuclei based on state-of-the-art chiral two- and three-nucleon forces. We observe that chiral two- and three-nucleon interactions (at N2LO and at N3LO) which have been found to predict realistic binding energies and radii for a wide range of finite nuclei (from p-shell nuclei up to nickel isotopes) are unable to saturate infinite nuclear matter. On the other hand, it has been shown that, when the fits of the cD and cE couplings of the chiral three-nucleon interactions include the constraint of nuclear matter saturation in addition to, as is typically the case, the triton binding energy, medium-mass nuclei are underbound and their radii are sytematically too large. We discuss this apparent inconsistency and perform test calculations for various scenarios to shed light on the issue.

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arXiv2019

Properties of isospin asymmetric matter derived from chiral effective field theory

We present and discuss properties of isospin asymmetric matter whose equation of state is derived from recent high-quality chiral nucleon-nucleon potentials and chiral effective three-nucleon forces. After a brief review of the chiral few-nucleon forces which we adopt, we concentrate on the symmetry energy and its density derivatives. We also explore the correlation between the symmetry energy at saturation density and its slope parameter, L. We estimate the truncation error across three orders of the chiral expansion for both the symmetry energy as a function of density and the slope parameter. Through an energy-density functional inspired by the liquid drop model, we establish a simple connection to finite nuclei. Specifically, we address the symmetry energy coefficient, the so-called reference (or equivalent) density, as well as the neutron skin thickness for 208Pb and 48Ca.

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arXiv2018

The radius of a typical-mass neutron star and chiral effective field theory

We calculate neutron star masses and radii from equations of state based on recent high-quality chiral nucleon-nucleon potentials up to fifth order of the chiral expansion and the leading chiral three- nucleon force. Our focus is on the radius of a 1.4 M_{Sun} neutron star, for which we report predictions that are consistent with the most recent constraints. We also show the full M(R) relations up to their respective maximum masses. Beyond the densities for which microscopic predictions are derived from chiral forces, the equations of state are obtained via polytropic continuations. However, the radius of a 1.4 M_{Sun} neutron star is nearly insensitive to the high-density extrapolation.

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arXiv2017

Proton skins, neutron skins, and proton radii of mirror nuclei

We present predictions for proton skins based on isospin-asymmetric equations of state derived microscopically from high-precision chiral few-nucleon interactions. Moreover, we investigate the relation between the neutron skin of a nucleus and the difference between the proton radii of the corresponding mirror nuclei.

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arXiv2016

Relativistic Effects and Three-Nucleon Forces in Nuclear Matter and Nuclei

We review a large body of predictions obtained within the framework of relativistic meson theory together with the Dirac-Brueckner-Hartree-Fock approach to nuclear matter and finite nuclei. The success of this method has been largely related to its ability to take into account important three-body effects. Therefore, the overarching theme of this article is the interpretation of the so-called "Dirac effects" as an effective three-nucleon force. We address the equation of state of isospin symmetric and asymmetric nucleonic matter and related issues, ranging from proton and neutron density distributions to momentum distributions and short-range correlations. A central part of the discussion is devoted to the optical model potential for nucleon-nucleus scattering. We also take the opportunity to explore similarities and differences with predictions based on the increasingly popular chiral effective field theory.

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arXiv2016

Investigation of constraints on few-neutron forces in neutron matter by empirical information on the neutron skin of 48Ca and 208Pb

The neutron matter equation of state is calculated from two-neutron forces up to fifth order of the chiral expansion and the order-by-order convergence of the predictions is investigated. Based on these equations of state, the binding energies and the neutron and proton density distributions in 208Pb and 48Ca are derived, with particular attention to the neutron skins, the focal point of this paper. Anticipating future experiments which will provide reliable information on the weak charge density in nuclei, the theoretical uncertainties and the possibility of constraining the size of few-neutron forces in neutron matter are discussed.

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