arXiv subjects

J. Margueron

Publications and source records attributed to J. Margueron.

At least 37 records · Page 2Linked to original sources

arXiv2019

Confronting gravitational-wave observations with modern nuclear physics constraints

Multi-messenger observations of neutron star (NS) mergers have the potential to revolutionize nuclear astrophysics. They will improve our understanding of nucleosynthesis, provide insights about the equation of state (EOS) of strongly-interacting matter at high densities, and enable tests of the theory of gravity and of dark matter. Here, we focus on the EOS, where both gravitational waves (GWs) from neutron-star mergers and X-ray observations from space-based detectors such as NICER will provide more stringent constraints on the structure of neutron stars. Furthermore, recent advances in nuclear theory have enabled reliable calculations of the EOS at low densities using effective field theory based Hamiltonians and advanced techniques to solve the quantum many-body problem. In this paper, we address how the first observation of GWs from GW170817 can be combined with modern calculations of the EOS to extract useful insights about the EOS of matter encountered inside neutron stars. We analyze the impact of various uncertainties, the role of phase transitions in the NS core, and discuss how future observations will improve our understanding of dense matter.

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arXiv2019

Constraining the properties of dense matter and neutron stars by combining nuclear physics and gravitational waves from GW170817

Gravitational waves from neutron-star mergers are expected to provide stringent constraints on the structure of neutron stars. At the same time, recent advances in nuclear theory have enabled reliable calculations of the low density equation of state using effective field theory based Hamiltonians and advanced techniques to solve the quantum many-body problem. In this paper, we address how the first observation of gravitational waves from GW170817 can be combined with modern calculations of the equation of state to extract useful insights about the equation of state of matter encountered inside neutron stars. We analyze the impact of various uncertainties and we show that the tidal deformability extracted from GW170817 is compatible, while less constraining, than modern nuclear physics knowledge.

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arXiv2018

A critical examination of constraints on the equation of state of dense matter obtained from GW170817

The correlation of the tidal polarizabilities $Λ_1$-$Λ_2$ for GW170817 is predicted by combining dense-matter equations of state (EOSs) that satisfy nuclear physics constraints with the chirp mass and mass asymmetry for this event. Our models are constrained by calculations of the neutron-matter EOS using chiral effective field theory Hamiltonians with reliable error estimates up to once or twice the nuclear saturation density. In the latter case, we find that GW170817 does not improve our understanding of the EOS. We contrast two distinct extrapolations to higher density: a minimal model (MM) which assumes that the EOS is a smooth function of density described by a Taylor expansion and a more general model parametrized by the speed of sound that admits phase transitions. This allows us to identify regions in the $Λ_1$-$Λ_2$ plots that could favor the existence of new phases of matter in neutron stars. We predict the combined tidal polarizability of the two neutron stars in GW170817 to be $80\le \tildeΛ\le 580$ ($280\le \tildeΛ\le 480$ for the MM), which is smaller than the range suggested by the LIGO-Virgo data analysis. Our analysis also shows that GW170817 requires a NS with $M=1.4M_\odot$ to have a radius $9.0<R_{1.4}<13.6$~km ($ 11.3 <R_{1.4}< 13.6$~km for the MM).

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arXiv2018

On the effect of high order empirical parameters on the nuclear equation of state

A quantitative knowledge of the nuclear Equation of State (EoS) requires an accurate estimation of the uncertainties on the EoS parameters and their mutual correlations. Such correlations are empirically observed in a large set of EoS models by different authors, but they are not always fully understood. We show that some of these correlations can be interpreted from basic physical constraints imposed on a simple Taylor expansion of the binding energy around saturation density. In particular, we investigate the correlations among the following empirical parameters: the symmetry energy $E_{sym}$, the slope and curvature of the symmetry energy $L_{sym}$ and $K_{sym}$, and the curvature and skewness of the binding energy in symmetric matter $K_{sat}$ and $Q_{sat}$. The uncertainties on these correlations is estimated through analytical modelling as well as a meta-modelling analysis of the EoS subject to physical constraints. We show that a huge dispersion of the correlations among low order empirical parameters is induced by the unknown higher order empirical parameters, such as $K_{sym}$ (second order) and $Q_{sat}$ and $Q_{sym}$ (third order). We also propose an explanation of the reason why $Q_{sat}$ is weakly constrained by present experimental data. We conclude that selective observables on high order parameters, such as $K_{sym}$ and $Q_{sat}$, should be better determined before the present uncertainties on the EoS can be further reduced.

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arXiv2018

$ΛΛ$ pairing in multi-strange hypernuclei

Multi-strange Ca, Sn and Pb hypernuclei with $ΛΛ$ pairing interaction are investigated within the Hartree-Fock-Bogoliubov approach. The unknown $ΛΛ$ pairing strength is calibrated to match with the maximal value for the prediction of the $Λ$ pairing gap in uniform matter for densities and isospin asymmetries equivalent to those existing in multi-$Λ$ hypernuclei. In this way, we provide an upper bound for the prediction of the $Λ$ pairing gap and its effects in hypernuclei. The condensation energy is predicted to be about 3~MeV as a maximum value, yielding small corrections on density distributions and shell structure. In addition, conditions on both Fermi energies and orbital angular momenta are expected to quench the nucleon-$Λ$ pairing for most of hypernuclei.

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arXiv2018

The equation of state for dense nucleonic matter from a metamodeling. I. Foundational aspects

A metamodeling for the nucleonic equation of state (EOS), inspired from a Taylor expansion around the saturation density of symmetric nuclear matter, is proposed and parameterized in terms of the empirical parameters. The present knowledge of nuclear empirical parameters is first reviewed in order to estimate their average values and associated uncertainties, and thus defining the parameter space of the metamodeling. They are divided into isoscalar and isovector type, and ordered according to their power in the density expansion. The goodness of the metamodeling is analyzed against the predictions of the original models. In addition, since no correlation among the empirical parameters is assumed a priori, all arbitrary density dependences can be explored, which might not be accessible in existing functionals. Spurious correlations due to the assumed functional form are also removed. This meta-EOS allows direct relations between the uncertainties on the empirical parameters and the density dependence of the nuclear equation of state and its derivatives, and the mapping between the two can be done with standard Bayesian techniques. A sensitivity analysis shows that the more influential empirical parameters are the isovector parameters $L_{sym}$ and $K_{sym}$, and that laboratory constraints at super-saturation densities are essential to reduce the present uncertainties. The present metamodeling for the EOS for nuclear matter is proposed for further applications in neutron stars and supernova matter.

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arXiv2018

The equation of state for dense nucleonic matter from a meta-modeling. II. Predictions for neutron stars properties

Employing a recently proposed metamodeling for the nucleonic matter equation of state we analyze neutron star global properties such as masses, radii, momentum of inertia, and others. The impact of the uncertainty on empirical parameters on these global properties is analyzed in a Bayesian statistical approach. Physical constraints, such as causality and stability, are imposed on the equation of state and different hypotheses for the direct Urca (dUrca) process are investigated. In addition, only metamodels with maximum masses above 2$M_\odot$ are selected. Our main results are the following: the equation of state exhibits a universal behavior against the dUrca hypothesis under the condition of charge neutrality and $β$-equilibrium; neutron stars, if composed exclusively of nucleons and leptons, have a radius of 12.7$\pm$0.4~km for masses ranging from 1 up to 2$M_\odot$; a small radius lower than 11~km is very marginally compatible with our present knowledge of the nuclear empirical parameters; and finally, the most important empirical parameters which are still affected by large uncertainties and play an important role in determining the radius of neutrons stars are the slope and curvature of the symmetry energy ($L_{sym}$ and $K_{sym}$) and, to a lower extent, the skewness parameters ($Q_{sat/sym}$).

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arXiv2017

Density Functional approach for multi-strange hypernuclei: competition between $Λ$ and $Ξ^{0,-}$ hyperons

The question of the competition between $Λ$ and $Ξ^{0,-}$ in the ground-state of multi-strange hypernuclei is addressed within a non-relativistic density functional approach, partially constrained by ab-initio calculations and experimental data. The exploration of the nuclear chart for $10<Z<120$ as a function of the strangeness number is performed by adding hyperons to a nuclear core imposing either conserved total charge $Q$ or conserved proton number $Z$. We find that almost all $Λ$ hypernuclei present an instability with respect to the strong interaction decay of $Λ$ towards $Ξ^{0,-}$ and that most of the instabilities generates $Ξ^-$ (resp. $Ξ^0$) in the case of conserved total charge $Q$ (resp. proton number $Z$). The strangeness number at which the first $Ξ^{0,-}$ appear is generally lower for configurations explored in the case of conserved $Q$ compared to the case of conserved $Z$, and corresponds to the crossing between the $Λ$ and the neutron or proton chemical potentials. About two to three hundred thousands pure $Λ$ hypernuclei may exist before the onset of $Ξ^{0,-}$. The largest uncertainty comes from the unknown $ΛΞ$ interaction, since the $NΛ$ and the $NΞ$ ones can be constrained by a few experimental data. The uncertainty on the $ΛΞ$ interaction can still modify the previous estimation by 30-40\%, while the impact of the unknown $ΞΞ$ interaction is very weak.

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arXiv2017

EoS constraints from nuclear masses and radii in a meta-modeling approach

The question of correlations among empirical equation of state (EoS) parameters constrained by nuclear observables is addressed in a fully empirical meta-modeling approach. A recently proposed meta-modeling for the nuclear EoS in nuclear matter, is augmented with a single finite size term to produce a minimal unified EoS functional able to describe the smooth part of the nuclear ground state properties. This meta-model can reproduce the predictions of a large variety of models, and interpolate continuously between them. The parameter space is sampled and filtered through the constraint of nuclear mass reproduction. We show that this simple analytical meta-modeling has a predictive power on masses, radii, and skins comparable to full HF or ETF calculations with realistic energy functionals. The covariance analysis on the posterior distribution shows that no physical correlation is present between the different EoS parameters. Concerning nuclear observables, a strong correlation between the slope of the symmetry energy and the neutron skin is observed, in agreement with previous studies.

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arXiv2017

Finite temperature pairing re-entrance in drip-line $^{48}$Ni nucleus

Finite-temperature Hartree-Fock-Bogoliubov theory using Skyrme interactions and Relativistic Hartree-Fock effective Lagrangians, predicts $^{48}$Ni as being a possible candidate for the finite temperature pairing re-entrance phenomenon. For this proton-drip-line nucleus, proton resonant states are expected to contribute substantially to pairing correlations and the two predicted critical temperatures are $T_{c1}\sim 0.08-0.2$~MeV and $T_{c2}\sim 0.7-0.9$~MeV. It is also shown that pairing re-entrance modifies the proton single particle energies around the Fermi level, as well as occupation numbers, and quasi-particle levels. The understanding of pairing re-entrance in $^{48}$Ni presently challenge our understanding of exotic matter under extreme conditions.

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arXiv2016

Can realistic interaction be useful for nuclear mean-field approaches?

Recent applications of the M3Y-type semi-realistic interaction to the nuclear mean-field approaches are presented: (i) Prediction of magic numbers and (ii) isotope shifts of nuclei with magic proton numbers. The results exemplify that realistic interaction, which is derived from the base $2N$ and $3N$ interaction, furnish a new theoretical instrument for advancing nuclear mean-field approaches.

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arXiv2015

Microscopic evaluation of the hypernuclear chart with $Λ$-hyperons

A large number of hypernuclei, where a considerable fraction of nucleons is replaced by strange baryons, and even pure hyperonic species are expected to be bound. Though, the hypernuclear landscape remains largely unknown because of scarce constraints on the $NY$ and $YY$ interactions. We want to estimate the number of potentially bound hypernuclei. In order to evaluate realistic error bars within the theoretical uncertainties associated to the spherical mean-field approach, and the present information from already synthetized hypernuclei on the $N-Y$ and $Y-Y$ channels, we limit ourselves to purely $Λ$-hypernuclei, to magic numbers of $Λ$'s (for Z $\leq$ 120 and $Λ\leq$70), and to even-even-even systems. We consider a density functional approach adjusted to microscopic Bruckner-Hartree-Fock calculations, where the $ΛΛ$ term is corrected in a phenomenological way, to reproduce present experimental constraints. The number of bound even-even-even $Λ$-hypernuclei is estimated to 491680 $\pm$ 34400. This relatively low uncertainty is due to the fact that the well constrained low density and highly unconstrained high density behavior of the energy functional turn out to be largely decoupled. Results in $Λ$-hypernuclei appear to be almost independent of the choice for the high-density part of the $ΛΛ$ interaction. The location of the $Λ$-hyperdriplines is also evaluated. Significant deviations from Iron-Nickel elements can be found for $Λ$-hypernuclei with the largest binding energy per baryon. Proton, neutron and $Λ$-hyperon magicity evolution and triple magic $Λ$-hypernuclei are studied. Possible bubbles and haloes effect in $Λ$-hypernuclei are also discussed.

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arXiv2015

Analytical mass formula and nuclear surface properties in the ETF approximation

The problem of the determination of the nuclear surface and surface symmetry energy is addressed in the framework of the Extended Thomas Fermi (ETF) approximation using Skyrme functionals. We propose an analytical model for the density profiles with variationally determined diffuseness parameters. For the case of symmetric nuclei, the resulting ETF functional can be exactly integrated, leading to an analytical formula expressing the surface energy as a function of the couplings of the energy functional. The importance of non-local terms is stressed, which cannot be simply deduced from the local part of the functional. In the case of asymmetric nuclei, we propose an approximate expression for the diffuseness and the surface energy. These quantities are analytically related to the parameters of the energy functional. In particular, the influence of the different equation of state parameters can be explicitly quantified. Detailed analyses of the different energy components (local/non-local, isoscalar/isovector, surface/curvature and higher order) are also performed. Our analytical solution of the ETF integral improves over previous models and leads to a precision better than 200 keV per nucleon in the determination of the nuclear binding energy for dripline nuclei.

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arXiv2015

Constraining the nuclear equation of state at subsaturation densities

Only one third of the nucleons in $^{208}$Pb occupy the saturation density area. Consequently nuclear observables related to average properties of nuclei, such as masses or radii, constrain the equation of state (EOS) not at saturation density but rather around the so-called crossing density, localised close to the mean value of the density of nuclei: $ρ\simeq$0.11 fm$^{-3}$. This provides an explanation for the empirical fact that several EOS quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative M of the energy at the crossing density is constrained by the giant monopole resonance (GMR) measurements in an isotopic chain rather than the incompressibility at saturation density. The GMR measurements provide M=1110 $\pm$ 70 MeV (6% uncertainty), whose extrapolation gives K$_\infty$=230 $\pm$ 40 MeV (17% uncertainty).

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arXiv2015

Heat capacity of low density neutron matter: from quantum to classical regimes

The heat capacity of neutron matter is studied over the range of densities and temperatures prevailing in neutron-star crusts, allowing for the transition to a superfluid phase at temperatures below some critical temperature $T_{sf}$ and including the transition to the classical limit. Finite temperature Hartree-Fock-Bogoliubov equations (FTHFB) are solved and compared to existing approximate expressions. In particular, the formula given by Levenfish and Yakovlev is found to reproduce the numerical results with a high degree of accuracy for temperatures $T\leq T_{sf}$. In the non-superfluid phase, $T\geq T_{sf}$, the linear approximation is valid only at temperature $T\ll T_{{\rm F} n}$ ($T_{{\rm F} n}$ being the Fermi temperature of the neutron gas) which is rarely the case in the shallow layers of the neutron star's crust. A non-perturbative interpolation between the quantal and the classical regimes is proposed here. The heat capacity, conveniently parametrized solely in terms of $T_{sf}$, $T_{{\rm F} n}$, and the neutron number density $n_n$, can be easily implemented in neutron-star cooling simulations.

astro-ph.SR↗

arXiv2014

A Cosmic Census of Radio Pulsars with the SKA

The Square Kilometre Array (SKA) will make ground breaking discoveries in pulsar science. In this chapter we outline the SKA surveys for new pulsars, as well as how we will perform the necessary follow-up timing observations. The SKA's wide field-of-view, high sensitivity, multi-beaming and sub-arraying capabilities, coupled with advanced pulsar search backends, will result in the discovery of a large population of pulsars. These will enable the SKA's pulsar science goals (tests of General Relativity with pulsar binary systems, investigating black hole theorems with pulsar-black hole binaries, and direct detection of gravitational waves in a pulsar timing array). Using SKA1-MID and SKA1-LOW we will survey the Milky Way to unprecedented depth, increasing the number of known pulsars by more than an order of magnitude. SKA2 will potentially find all the Galactic radio-emitting pulsars in the SKA sky which are beamed in our direction. This will give a clear picture of the birth properties of pulsars and of the gravitational potential, magnetic field structure and interstellar matter content of the Galaxy. Targeted searches will enable detection of exotic systems, such as the ~1000 pulsars we infer to be closely orbiting Sgr A*, the supermassive black hole in the Galactic Centre. In addition, the SKA's sensitivity will be sufficient to detect pulsars in local group galaxies. To derive the spin characteristics of the discoveries we will perform live searches, and use sub-arraying and dynamic scheduling to time pulsars as soon as they are discovered, while simultaneously continuing survey observations. The large projected number of discoveries suggests that we will uncover currently unknown rare systems that can be exploited to push the boundaries of our understanding of astrophysics and provide tools for testing physics, as has been done by the pulsar community in the past.

astro-ph.IM↗

arXiv2014

Pairing correlations of cold fermionic gases at overflow from a narrow to a wide harmonic trap

Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior of superfluid Fermi systems when they pass from a small to a large container. Such systems can be now realized thanks to recent progress in experimental techniques. It will allow to better understand pairing properties at overflow and in general in rapidly varying external potentials.

cond-mat.quant-gas↗

arXiv2014

Spin-isospin Response in Finite Nuclei from an Extended Skyrme Interaction

The magnetic dipole (M1) and the Gamow-Teller (GT) excitations of finite nuclei have been studied in a fully self-consistent Hartree-Fock (HF) plus random phase approximation (RPA) approach by using a Skyrme energy density functional with spin and spin-isospin densities. To this end, we adopt the extended SLy5st interaction which includes spin-density dependent terms and stabilize nuclear matter with respect to spin instabilities. The effect of the spin-density dependent terms is examined in both the mean field and the spin-flip excited state calculations. The numerical results show that those terms give appreciable repulsive contributions to the M1 and GT response functions of finite nuclei.

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