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P. A. M. Guichon

Publications and source records attributed to P. A. M. Guichon.

At least 19 recordsLinked to original sources
arXiv2022

Dense Nuclear Matter with Baryon Overlap

The possibility of new short-distance physics applicable inside the cores of NS is incorporated into the equation of state generated by the quark-meson coupling model. The contribution of this new physics to the energy density is taken to be proportional to the amount of overlap between the quark cores of the baryons involved. With no change to the properties of symmetric nuclear matter at saturation density, including an incompressibility compatible with data on giant monopole resonances, one can sustain neutron stars with a maximum mass $M_{max}>2.1$ M$_\odot$, even when hyperons are included.

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arXiv2021

Equation of State of Hot Dense Hyperonic Matter in the Quark-Meson-Coupling (QMC-A) model

We report a new equation of state (EoS) of cold and hot hyperonic matter constructed in the framework of the quark-meson-coupling (QMC-A) model. The QMC-A EoS yields results compatible with available nuclear physics constraints and astrophysical observations. It covers the range of temperatures from T=0 to 100 MeV, entropies per particle S/A between 0 and 6, lepton fractions from Y$_L$=0.0 to 0.6, and baryon number densities n$_B$=0.05-1.2 fm$^{-3}$. Applications of the QMC-A EoS are made to cold neutron stars (NS) and to hot proto-neutron stars (PNS) in two scenarios, (i) lepton rich matter with trapped neutrinos and (ii) deleptonized chemically equilibrated matter. We find that the QMC-A model predicts hyperons in amounts growing with increasing temperature and density, thus suggesting not only their presence in PNS but also, most likely, in NS merger remnants. The nucleon-hyperon phase transition is studied through the adiabatic index and the speed of sound c$_s$. It is shown that the lowering of (c$_s$/c)$^2$ to and below the conformal limit of 1/3 is a general consequence of instabilities due to any phase transition and is not a unique fingerprint of the hadron-quark matter transition. Rigid rotation of cold and hot stars, their moments of inertia and Kepler frequencies are also explored. The QMC-A model results are compared with two relativistic models, the chiral mean field model (CMF), and the generalized relativistic density functional with hyperons (GRDF-Y). Similarities and differences are discussed.

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arXiv2021

On the Speed of Sound in Hyperonic Stars

We build upon the remarkable, model independent constraints on the equation of state of dense baryonic matter established recently by Annala et al. [1]. Using the quark-meson coupling model, an approach to nuclear structure based upon the self-consistent adjustment of hadron structure to the local meson fields, we show that, once hyperons are allowed to appear in dense matter in \b{eta}-equilibrium, the equation of state is consistent with those constraints. As a result, while one cannot rule out the occurence of quark matter in the cores of massive neutron stars, the available constraints are also compatible with the presence of hyperons.

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arXiv2019

Physics of even-even superheavy nuclei with 96 < Z < 110 in the Quark-Meson-Coupling Model

The Quark-Meson-Coupling (QMC) model has been applied to the study of the properties of even-even super-heavy nuclei with 96 < Z < 110, over a wide range of neutron numbers. The aim is to identify the deformed shell gaps at N = 152 and N = 162 predicted in macroscopic-microscopic (macro-micro) models, in a model based on the mean-field Hartree-Fock+BCS approximation. The predictive power of the model has been tested on proton and neutron spherical shell gaps in light doubly closed (sub)shell nuclei. In the super-heavy region, the ground state binding energies of 98 < Z < 110 and 146 < N < 160 differ, in the majority of cases, from the measured values by less than 2.5 MeV, with the deviation decreasing with increasing Z and N. The axial quadrupole deformation parameter, calculated over the range of neutron numbers 138 < N < 184, revealed a prolate-oblate coexistence and shape transition around N = 168, followed by an oblate-spherical transition towards the expected N = 184 shell closure in Cm, Cf, Fm and No. The closure is not predicted in Rf, Sg, Hs and Ds as another shape transition to a highly deformed shape in Sg, Hs and Ds for N > 178 appears, while 288Rf (N = 184) remains oblate. The bulk properties predicted by QMC are found to have a limited sensitivity to the deformed shell gaps at N = 152 and 162. However, the evolution of the neutron single-particle spectra with 0 < beta2 < 0.55 gives unambiguous evidence for the location and size of the N = 152 and 162 gaps as a function of Z and N. In addition, the neutron number dependence of neutron pairing energies provides supporting evidence for existence of the energy gaps.

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arXiv2019

Do Delta Baryons Play a Role in Neutron Stars?

The presence of exotic hadrons, such as hyperons and $Δ$ isobars, in the dense nuclear matter in their cores has been shown to produce important changes in the properties of neutron stars. Within the quark-meson coupling model, we show that the many-body forces generated by the change in the internal quark structure of the baryons in the strong scalar mean fields generated in dense nuclear matter prohibit the appearance of $Δ$ isobars.

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arXiv2019

Isovector Effects in Neutron Stars, Radii and the GW170817 Constraint

An isovector-scalar meson is incorporated self-consistently into the quark-meson coupling description of nuclear matter and its most prominent effects on the structure of neutron stars are investigated. The recent measurement of GW170817 is used to constrain the strength of the isovector-scalar channel. With the imminent measurements of the neutron star radii in the NICER mission it is particularly notable that the inclusion of the isovector-scalar force has a significant impact. Indeed, the effect of this interaction on the neutron star radii and masses is larger than the uncertainties introduced by variations in the parameters of symmetric nuclear matter at saturation, namely the density, binding energy per nucleon and the symmetry energy. In addition, since the analysis of GW170817 has provided constraints on the binary tidal deformability of merging neutron stars, the predictions for this parameter within the quark-meson coupling model are explored, as well as the moment of inertia and the quadrupole moment of slowly rotating neutron stars.

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arXiv2018

Neutron to Dark Matter Decay in Neutron Stars

Recent proposals have suggested that a previously unknown decay mode of the neutron into a dark matter particle could solve the long lasting measurement problem of the neutron decay width. We show that, if the dark particle in neutron decay is the major component of the dark matter in the universe, this proposal is in disagreement with modern astro-physical data concerning neutron star masses.

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arXiv2018

Quark-Meson-Coupling (QMC) model for finite nuclei, nuclear matter and beyond

The Quark-Meson-Coupling model, which self-consistently relates the dynamics of the internal quark structure of a hadron to the relativistic mean fields arising in nuclear matter, provides a natural explanation to many open questions in low energy nuclear physics, including the origin of many-body nuclear forces and their saturation, the spin-orbit interaction and properties of hadronic matter at a wide range of densities up to those occurring in the cores of neutron stars. Here we focus on four aspects of the model (i) a full comprehensive survey of the theory, including the latest developments, (ii) extensive application of the model to ground state properties of finite nuclei and hypernuclei, with a discussion of similarities and differences between the QMC and Skyrme energy density functionals, (iii) equilibrium conditions and composition of hadronic matter in cold and warm neutron stars and their comparison with the outcome of relativistic mean-field theories and, (iv) tests of the fundamental idea that hadron structure changes in-medium.

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arXiv2018

Implications of Neutron Star Properties for the Existence of Light Dark Matter

It was recently suggested that the discrepancy between two methods of measuring the lifetime of the neutron may be a result of an unseen decay mode into a dark matter particle which is almost degenerate with the neutron. We explore the consequences of this for the properties of neutron stars, finding that their known properties are in conflict with the existence of such a particle.

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arXiv2017

Lambda beta-decay in-medium

Under the working hypothesis that the structure of a bound hadron is modified by its interactions with other hadrons, one may expect to see changes in carefully chosen observables. In the light of a recent proposal to measure the axial charge in the strangeness changing beta-decay of a bound Lambda hyperon, we examine the size of the change expected within the quark-meson coupling model. It is predicted to be significant.

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arXiv2016

Finite Nuclei in the Quark-Meson Coupling (QMC) Model

We report the first use of the effective QMC energy density functional (EDF), derived from a quark model of hadron structure, to study a broad range of ground state properties of even-even nuclei across the periodic table in the non-relativistic Hartree-Fock+BCS framework. The novelty of the QMC model is that the nuclear medium effects are treated through modification of the internal structure of the nucleon. The density dependence is microscopically derived and the spin-orbit term arises naturally. The QMC EDF depends on a single set of four adjustable parameters having clear physical basis. When applied to diverse ground state data the QMC EDF already produces, in its present simple form, overall agreement with experiment of a quality comparable to a representative Skyrme EDF. There exist however multiple Skyrme paramater sets, frequently tailored to describe selected nuclear phenomena. The QMC EDF set of fewer parameters, as derived in this work, is not open to such variation, chosen set being applied, without adjustment, to both the properties of finite nuclei and nuclear matter.

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arXiv2015

The E00-110 experiment in Jefferson Lab's Hall A: Deeply Virtual Compton Scattering off the Proton at 6 GeV

We present final results on the photon electroproduction ($\vec{e}p\rightarrow epγ$) cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region from Jefferson Lab experiment E00-110. Results from an analysis of a subset of these data were published before, but the analysis has been improved which is described here at length, together with details on the experimental setup. Furthermore, additional data have been analyzed resulting in photon electroproduction cross sections at new kinematic settings, for a total of 588 experimental bins. Results of the $Q^2$- and $x_B$-dependences of both the helicity-dependent and helicity-independent cross sections are discussed. The $Q^2$-dependence illustrates the dominance of the twist-2 handbag amplitude in the kinematics of the experiment, as previously noted. Thanks to the excellent accuracy of this high luminosity experiment, it becomes clear that the unpolarized cross section shows a significant deviation from the Bethe-Heitler process in our kinematics, compatible with a large contribution from the leading twist-2 DVCS$^2$ term to the photon electroproduction cross section. The necessity to include higher-twist corrections in order to fully reproduce the shape of the data is also discussed. The DVCS cross sections in this paper represent the final set of experimental results from E00-110, superseding the previous publication.

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arXiv2012

Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q^2=0.92 and 1.76 GeV^2

Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1.76 GeV^2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q^2-range, and point to their non-trivial behavior.

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arXiv2011

Fermi matrix element with isospin breaking

Prompted by the level of accuracy now being achieved in tests of the unitarity of the CKM matrix, we consider the possible modification of the Fermi matrix element for the $β$-decay of a neutron, including possible in-medium and isospin violating corrections. While the nuclear modifications lead to very small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected, the effect of the $u-d$ mass difference on the conclusion concerning $V_{ud}$ is no longer insignificant. Indeed, we suggest that the correction to the value of $|V_{ud}|^2 \, + \, |V_{us}|^2 \, + \, |V_{ub}|^2$ is at the level of $10^{-4}$.

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arXiv2010

Role of Hyperons in Neutron Stars

The latest observation of a Shapiro delay of the binary millisecond pulsar J1614-2230 by Demorest et al. Nature 467 1081 (2010) yielded the pulsar gravitational mass to be 1.97 +/- 0.04 solar mass, the heaviest observed pulsar to-date. This result produces a stringent constraint on Equation(s) of State (EoS) of high density neutron star matter. One of the main conclusions of Demorest et al. was that their result makes the presence of non-nucleonic components in the neutron star matter unlikely. We compare the result with our recent work and conclude that hyperons in high-density matter are fully consistent with the observation and that their presence is a necessary consequence of general physical laws.

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arXiv2010

Hypernuclei in the quark-meson coupling model

We present results of hypernuclei calculated in the latest quark-meson coupling (QMC) model, where the effect of the mean scalar field in-medium on the one-gluon exchange hyperfine interaction, is also included self-consistently. The extra repulsion associated with this increased hyperfine interaction in-medium completely changes the predictions for Σ hypernuclei. Whereas in the earlier version of QMC they were bound by an amount similar to Λ hypernuclei, they are unbound in the latest version of QMC, in qualitative agreement with the experimental absence of such states.

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arXiv2006

Cold uniform matter and neutron stars in the quark-mesons-coupling model

A new density dependent effective baryon-baryon interaction has been recently derived from the quark-meson-coupling (QMC) model, offering impressive results in application to finite nuclei and dense baryon matter. This self-consistent, relativistic quark-level approach is used to construct the Equation of State (EoS) and to calculate key properties of high density matter and cold, slowly rotating neutron stars. The results include predictions for the maximum mass of neutron star models, together with the corresponding radius and central density, as well the properties of neutron stars with mass of order 1.4 $M_\odot$. The cooling mechanism allowed by the QMC EoS is explored and the parameters relevant to slow rotation, namely the moment of inertia and the period of rotation investigated. The results of the calculation, which are found to be in good agreement with available observational data, are compared with the predictions of more traditional EoS. The QMC EoS provides cold neutron star models with maximum mass 1.9--2.1 M$_\odot$, with central density less than 6 times nuclear saturation density ($n_{0}= 0.16 {\rm fm}^{-3}$) and offers a consistent description of the stellar mass up to this density limit. In contrast with other models, QMC predicts no hyperon contribution at densities lower than $3n_0$, for matter in $β$-equilibrium. At higher densities, $Ξ^{-,0}$ and $Λ$ hyperons are present.

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