We study how the $Λ$ hyperon threshold influences the radius of the canonical $1.4 ~M_\odot$ neutron star in the light of the measurements found in the recent literature. We show that the onset of a new degree of freedom not only causes the well known reduction of the maximum mass, but also compacts the neutron stars with high central density. With the help of the strange mesons $ϕ$ and $σ^*$, we show that it is possible to simulate very compact neutron stars keeping realistic hyperon potentials, $U_Λ(n_0)= -28$ MeV and $ U_Λ^Λ(n_0/5)$ in agreement with recents measurements. In the end we generalize these results showing that the onset of a yet not known dark matter particle with mass of 1.04 GeV is able to produce simultaneously a 2 $M_\odot$ neutron star and a canonical one with a radius of only 11.62 km.
Radiative decays of decuplet hyperons and octet hyperon charge radii are evaluated in a chiral constituent quark model emphasizing the role of exchange currents. Exchange currents largely cancel for the M1 decay amplitudes, while they dominate the E2 amplitude. Due to the pseudoscalar meson cloud the charge radii of Sigma^- and Xi^- are almost as large as the proton radius, in agreement with recent experimental results from SELEX. Strangeness suppression is weakened by exchange currents for several observables.
Octet hyperon charge radii are calculated in a chiral constituent quark model including electromagnetic exchange currents between quarks. In impulse approximation one observes a decrease of the hyperon charge radii with increasing strangeness. This effect is reduced by exchange currents. Due to exchange currents, the charge radius of the negatively charged hyperons are close to the proton charge radius.
The momentum projected SU(3) Chiral Color Dielectric Model (CCDM) is employed to calculate the charge root mean square radii and charge distributions of hyperons. We compare our result with Skyrme, MIT bag and Cloudy Bag model results. The charge distribution of $Λ$ in CCDM is similar to that of Skyrme Model prediction.
The pion mass dependence of hyperon electromagnetic properties is determined using two-flavor heavy baryon chiral perturbation theory. Specifically we compute chiral corrections to the charge radii, magnetic moments, and magnetic radii of the spin one-half hyperons, as well as the charge radii, magnetic moments, magnetic radii, electric quadrupole moments, and quadrupole radii of the spin three-half hyperons. Results for the nucleon and delta are also included. Efficacy of the two-flavor theory is investigated by analyzing the role played by virtual kaons. For the electromagnetic properties of…
We obtain a new equation of state for the nucleonic and hyperonic inner core of neutron stars that fulfills the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km. The nucleonic equation of state is obtained from a new parametrization of the FSU2 relativistic mean-field functional that satisfies these latest astrophysical constraints and, at the same time, reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions. On the one hand, the equation of state of neut…
We have studied quasielastic charged current hyperon production induced by $\barν_μ$ on free nucleon and the nucleons bound inside the nucleus and the results are presented for several nuclear targets like $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$. The hyperon-nucleon transition form factors are determined from neutrino-nucleon scattering and semileptonic decays of neutron and hyperons using SU(3) symmetry. The nuclear medium effects(NME) due to Fermi motion and final state interaction(FSI) effect due to hyperon-nucleon scattering have been taken into account. Also we have studied two pion productio…
Two-flavor chiral expansions provide a useful perturbative framework to study hadron properties. Such expansions should exhibit marked improvement over the conventional three-flavor chiral expansion. Although one can theoretically formulate two-flavor theories for the various hyperon multiplets, the nearness of kaon thresholds can seriously undermine the effectiveness of the perturbative expansion in practice. We investigate the importance of virtual kaon thresholds on hyperon properties, specifically their masses and isovector axial charges. Using a three-flavor expansion that includes SU(3) …
The existence of 2 Msun pulsars puts very strong constraints on the equation of state (EOS) of neutron stars (NSs) with hyperon cores, which can be satisfied only by special models of hadronic matter. The radius-mass relation for these models is sufficiently specific that it could be subjected to an observational test with future X-ray observatories. We want to study the impact of the presence of hyperon cores on the radius-mass relation for NS. We aim to find out how, and for which particular stellar mass range, a specific relation R(M), where M is the gravitational mass, and R is the circumf…
The vacuum fluctuation (VF) effects on the properties of the hyperonic neutron star matter are investigated in the framework of the relativistic mean field (RMF) theory. The VF corrections result in the density dependence of in-medium baryon and meson masses. We compare our results obtained by adopting three kinds of meson-hyperon couplings. The introduction of both hyperons and VF corrections soften the equation of state (EoS) for the hyperonic neutron star matter and hence reduce hyperonic neutron star masses. The presence of the $δ$ field enlarges the masses and radii of hyperonic neutron s…
The measured electromagnetic form factors of $Λ$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $ϕ$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\bar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.
We present two recent parametrizations of the equation of state (FSU2R and FSU2H models) that reproduce the properties of nuclear matter and finite nuclei, fulfill constraints on high-density matter stemming from heavy-ion collisions, produce 2$M_{\odot}$ neutron stars, and generate neutron star radii below 13 km. Making use of these equations of state, cooling simulations for isolated neutron stars are performed. We find that two of the models studied, FSU2R (with nucleons) and, in particular, FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without…
Within the framework of quantum molecular dynamics transport model, the isospin and in-medium effects on the hyperon production in the reaction of $^{197}$Au + $^{197}$Au are investigated thoroughly. A repulsive hyperon-nucleon potential from the chiral effective field theory is implemented into the model, which is related to the hyperon momentum and baryon density. The correction on threshold energy of the elementary hyperon cross section is taken into account. It is found that the $Σ$ yields are suppressed in the domain of midrapidity and kinetic energy spectra with the potential. The hypero…
We present results on deep sub threshold hyperon production in nuclear collisions, with the UrQMD transport model. Introducing anti-kaon+baryon and hyperon+hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in Ar+KCl reactions at $E_{lab}=1.76$ A GeV. We find that the hyperon strangeness exchange is the dominant process contributing to the $Ξ^-$ yield, however remains short of explaining the $Ξ^-/Λ$ ratio measured with the HADES experiment. We also discuss possible reasons for the discrepancy with previous studies and th…
We perform cooling simulations for isolated neutron stars using recently developed equations of state for their core. The equations of state are obtained from new parametrizations of the FSU2 relativistic mean-field functional that reproduce the properties of nuclear matter and finite nuclei, while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions, measurements of massive 2$M_{\odot}$ neutron stars, and neutron star radii below 13 km. We find that two of the models studied, FSU2R (with nucleons) and in particular FSU2H (with nucleons and hyperons), show very …
The near-threshold $e^+e^- \to Λ\barΛ$ reaction is studied with the assumption that the production mechanism is due to a near-$Λ\barΛ$-threshold bound state. The cross section of $e^+e^- \to Λ\barΛ$ reaction is parametrized in terms of the electromagnetic form factors of $Λ$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^+e^- \to Λ\barΛ$ reaction from a new narrow state with quantum numbers $J^{PC}=1^{--}$ is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the ma…
We study the mechanism of the associated Lambda-kaon and Sigma-kaon production in nucleon-nucleon collisions over an extended range of near threshold beam energies within an effective Lagrangian model, to understand of the new data on pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions published recently by the COSY-11 collaboration. In this theory, the hyperon production proceeds via the excitation of N*(1650), N*(1710), and N*(1720) baryonic resonances. Interplay of the relative contributions of various resonances to the cross sections, is discussed as a function of the beam energy over a la…
Two-flavor chiral expansions provide a useful perturbative framework to study hadron properties. Such expansions should exhibit marked improvement over the conventional three-flavor chiral expansion. Although in principle one can formulate two-flavor theories for the various hyperon multiplets, the nearness of kaon thresholds can seriously undermine the effectiveness of such two-flavor theories in practice. We investigate the importance of virtual kaon thresholds on hyperon properties, specifically their isovector axial charges and electromagnetic observables. In particular we uncover the unde…
In this paper the impact of the strength of hyperon-nucleon and hyperon-hyperon on the maximum neutron star mass is shown. The strong hyperon-hyperon coupling constant together with the additional nonlinear meson interaction terms lead to the essential softening of the equation of state and to the existence of another more compact branch of stable neutron star configurations. The analysis of the mass-radius relations leads to the conclusion that the additional stable configurations of hyperon-rich neutron stars are characterized by the reduced value of radii.
We present results from Brueckner-Hartree-Fock calculatons for beta stable neutron star matter with nucleonic and hyperonic degress degrees of freedom, employing the most recent parametrizations of the baryon-baryon interaction of the Nijmegen group. It is found that the only strange baryons emergin in beta stable matter up to total barionic densities of 1.2 fm^-3 are $Σ^-$ and $Λ$. The corresponding equations of state are then used to compute properties of neutron stars such as masses and radii.
We study the antikaon-induced inclusive cascade $Ξ^-$ hyperon production from $^{12}$C and $^{184}$W target nuclei near threshold within a nuclear spectral function approach. The approach describes incoherent direct $Ξ^-$ hyperon production in elementary ${K^-}p \to {K^+}Ξ^-$ and ${K^-}n \to {K^0}Ξ^-$ processes as well as takes into account the influence of the scalar nuclear $K^-$, $K^+$, $K^0$, $Ξ^-$ and their Coulomb potentials on these processes. We calculate the absolute differential and total cross sections for the production of $Ξ^-$ hyperons off these nuclei at laboratory angles $\le$ …
Recent progress in the understanding of the high density phase of neutron stars advances the view that a substantial fraction of the matter consists of hyperons. The possible impacts of a highly attractive interaction between hyperons on the properties of compact stars are investigated. We find that a hadronic equation of state with hyperons allows for a first order phase transition to hyperonic matter. The corresponding hyperon stars can have rather small radii of R=8 km.
We study the near-threshold inclusive photoproduction of $Ξ^-$ hyperons off $^{12}$C and $^{184}$W target nuclei within a first-collision model relying on the nuclear spectral function and including incoherent $Ξ^-$ production in direct elementary $γp \to K^+{K^+}Ξ^-$ and $γn \to K^+{K^0}Ξ^-$ processes. The model takes into account the impact of the nuclear effective scalar $K^+$, $K^0$, $Ξ^-$ and their Coulomb potentials on these processes as well as the absorption of final $Ξ^-$ hyperons in nuclear matter, the binding of intranuclear nucleons and their Fermi motion. We calculate the absolute…
Based on the Kaplan-Nelson Lagrangian, we investigate kaon condensation in dense neutron star matter allowing for the explicit presence of hyperons. Using various models we find that the condensate threshold is sensitive to the behavior of the scalar density; the more rapidly it increases with baryon density, the lower is the threshold for condensation. The presence of hyperons, particularly the $Σ^-$, shifts the threshold for $K^-$ condensation to a higher density. In the mean field approach, with hyperons, the condensate amplitude grows sufficiently rapidly that the nucleon effective mass va…
We study the pion-induced inclusive $Λ(1520)$ hyperon production from nuclei near threshold within a nuclear spectral function approach accounting for incoherent primary $π^-$ meson--proton ${π^-}p \to K^0Λ(1520)$ production processes. We calculate the absolute differential and total cross sections for the production of $Λ(1520)$ hyperons off carbon and tungsten nuclei at laboratory angles of 0$^{\circ}$--10$^{\circ}$, 10$^{\circ}$--45$^{\circ}$ and 45$^{\circ}$--85$^{\circ}$ by $π^-$ mesons with momentum of 1.7 GeV/c as well as their relative (transparency ratio) differential and integral yie…
We present a theoretical investigation of $Λ(1520)$ attenuation in $γA$ reactions near the threshold. It is performed in the framework of a collision model based on the nuclear spectral function. The model accounts for both primary photon-nucleon $γN \to KΛ(1520)$ and secondary pion-nucleon $πN \to KΛ(1520)$ production processes. We calculate the target mass and momentum dependences of the forward $Λ(1520)$ hyperon production from nuclei at photon energy of 2 GeV as well as for two options for its in-medium width. We find that the considered dependences are markedly sensitive to this width. Ou…
In this work, masses and radii of neutron stars are considered to investigate the effect of nuclear symmetry energy to the astrophysical observables. A relativistic mean field model with density-dependent meson-baryon coupling constants is employed in describing the equation of state of dense nuclear matter, and the density dependencies of the symmetry energies are quoted from the recent phenomenological formulae obtained from the heavy ion data at subnuclear saturation densities. Since hyperons can take part in the $β$-equilibrium of the dense matter inside neutron stars, we include hyperons …
In the framework of the nuclear spectral function approach for incoherent primary proton-nucleon and secondary pion-nucleon production processes we study the inclusive Lambda(1520) hyperon production in the interaction of 2.83 GeV protons with nuclei. In particular, the A and momentum dependences of the absolute and relative Lambda(1520) hyperon yields are investigated in two scenarios for its in-medium width. Our model calculations show that the pion-nucleon production channel contributes distinctly to the "low-momentum" Lambda(1520) creation both in light and heavy nuclei in the chosen kinem…
We report our recent effort for the extraction of resonance parameters (complex pole mass and residues etc.) associated with Lambda* and Sigma* hyperons. This was accomplished via a comprehensive partial-wave analysis of the data for K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi reactions from the thresholds up to W=2.1 GeV within a dynamical coupled-channels approach. The results suggest a possible existence of new narrow J^P=3/2^+ Λresonance with pole mass 1671^{+2}_{-8} -i(5^{+11}_{-2}) MeV, located close to the eta Lambda threshold. This resonance is found to be responsible for r…
The $Δ$-isobar degrees of freedom are included in the covariant density functional (CDF) theory to study the equation of state (EoS) and composition of dense matter in compact stars. In addition to $Δ$'s we include the full octet of baryons, which allows us to study the interplay between the onset of delta isobars and hyperonic degrees of freedom. Using both the Hartree and Hartree-Fock approximation we find that $Δ$'s appear already at densities slightly above the saturation density of nuclear matter for a wide range of the meson-$Δ$ coupling constants. This delays the appearance of hyperons …
We present results from Brueckner-Hartree-Fock calculations for $β$-stable neutron star matter with nucleonic and hyperonic degrees of freedom employing the most recent parametrizations of the baryon-baryon interaction of the Nijmegen group. Only $Σ^-$ and $Λ$ are present up to densities $\sim 7ρ_0$. The corresponding equations of state are then used to compute properties of neutron stars such as masses and radii.
Evolution of strangeness and hyperons in quarkyonic matter
Institute for Nuclear Theory, University of Washington（华盛顿大学核理论研究所）；Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), RIKEN（理化学研究所跨学科理论与数学科学项目（iTHEMS））；Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）；Theory Center, IPNS, High Energy Accelerator Research Organization (KEK)（高能加速器研究机构（KEK）IPNS理论中心）；Department of Physics, Tohoku University（东北大学物理系）
Since the discovery of neutron stars with masses around 2 solar masses the composition of matter in the central part of these massive stars has been intensively discussed. Within this paper we will (re)investigate the question of the appearance of hyperons. To that end we will perform an extensive parameter study within relativistic mean field models. We will show that it is possible to obtain high mass neutron stars (i) with a substantial amount of hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses, and (iii) a spinodal instability at the onset of hyperons. The result…
We present results from many-body calculations for β-stable neutron star matter with nucleonic and hyperonic degrees of freedom, employing the most recent parametrizations of the baryon-baryon interaction of the Nijmegen group. It is found that the only strange baryons emerging in β-stable matter up to total baryonic densities of 1.2 fm^{-3} are Σ^- and Λ. The corresponding equations of state are thence used to compute properties of neutron stars such as the masses, moments of inertia and radii. We also study the possibility of forming a hyperon superfluid and discuss its implications for neut…
The existence of neutron stars with $2M_\odot$ requires the strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-pomeron exchange potential (MPP) working universally among 3- and 4-baryons to stiffen the EoS. Its strength is restricted by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The EoSs are derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational method (CVM) with the nuclear interactions ESC and AV18. The mass-radius relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV) equation, where…
Properties of neutron stars with hyperons within a generalized relativistic approach
Universidad de Salamanca（萨拉曼卡大学）；Université de Liège（列日大学）；Université Libre de Bruxelles（布鲁塞尔自由大学）；Université Claude Bernard Lyon 1（里昂第一大学）；Université de Caen Normandie（诺曼底大学）；Institut Universitaire de France (IUF)（法国高等研究院）；CNRS/IN2P3（法国国家科学研究中心/欧洲核子研究委员会）；Université de Strasbourg（斯特拉斯堡大学）；Observatoire astronomique de Strasbourg, CNRS（斯特拉斯堡天文台）；CNRS, Observatoire de Paris, Université PSL（法国国家科学研究中心，巴黎天文台，巴黎文理研究大学）
We reexamine the equation of state for the nucleonic and hyperonic inner core of neutron stars that satisfies the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km, while fulfilling the saturation properties of nuclear matter and finite nuclei together with the constraints on the high-density nuclear pressure coming from heavy-ion collisions. The recent nucleonic FSU2R and hyperonic FSU2H models are fine tuned improving the density dependence of pure neutron matter at subsaturation densities. The corresponding nuclear matter properties at saturation, t…
We investigate compact star properties within the quark meson coupling model (QMC) with a soft symmetry energy density dependence at large densities. In particular, the hyperon content and the mass/radius curves for the families of stars obtained within the model are discussed. The hyperon-meson couplings are chosen according to experimental values of the hyperon nuclear matter potentials, and possible uncertainties are considered. It is shown that a softer symmetry energy gives rise to stars with less hyperons, smaller radii and larger masses. Hyperon-meson couplings may also have a strong ef…
Recent neutron star observations suggest that the masses and radii of neutron stars may be smaller than previously considered, which would disfavor a purely nucleonic equation of state. In our model, we use a the flavor SU(3) sigma model that includes delta resonances and hyperons in the equation of state. We find that if the coupling of the delta resonances to the vector mesons is slightly smaller than that of the nucleons, we can reproduce both the measured mass-radius relationship and the extrapolated equation of state.
The $\bar{K} + N \to K + Ξ$ reaction is studied for center-of-momentum energies ranging from threshold to 3 GeV in an effective Lagrangian approach that includes the hyperon $s$- and $u$-channel contributions as well as a phenomenological contact amplitude. The latter accounts for the rescattering term in the scattering equation and possible short-range dynamics not included explicitly in the model. Existing data are well reproduced and three above-the-threshold resonances were found to be required to describe the data, namely, the $Λ(1890)$, $Σ(2030)$, and $Σ(2250)$. For the latter resonance …
We investigate the quantum hadrodynamic equation of state for neutron stars (with and without including hyperons) in the presence of strong magnetic fields. The deduced masses and radii are consistent with recent observations of high mass neutron stars even in the case of hyperonic nuclei for sufficiently strong magnetic fields. The calculated adiabatic index and the moments of inertia for magnetized neutron stars exhibit rapid changes with density. This may provide some insight into the mechanism of star-quakes and flares in magnetars.
Bulk properties of cold and hot neutron stars (NSs) are studied on the basis of the hadron-quark crossover picture where a smooth transition from the hadronic phase to the quark phase takes place at finite baryon density. By using a phenomenological equation of state (EOS) "CRover" which interpolates the two phases at around 3 times the nuclear matter density, it is found that the cold NSs with the gravitational mass larger than 2-solarmass can be sustained. This is in sharp contrast to the case of the first-order hadron-quark transition. The radii of the cold NSs with the CRover EOS are in th…
The structure of neutron stars is determined by the equation of state of the matter inside the star, which relies on the knowledge of nuclear interactions. While radii of neutron stars mostly depend on the equation of state of neutron matter at nuclear densities, their maximum mass can be drastically affected by the appearance of hyperons at higher densities in the inner core of the star. We summarize recent quantum Monte Carlo results on the calculation of the equation of state of neutron matter at nuclear and higher densities. We report about the development of realistic hyperon-nucleon inte…
We use the Isospin Quantum Molecular Dynamics approach supplemented with a phase space coalescence to study the properties of the production of hypertritons. We see strong influences of the hyperon rescattering on the yields. The hypertritons show up to be quite aligned to the properties of nuclear matter underlining the necessity of rescattering to transport the hyperons to the spectator matter.
Nuclear effective interactions are considered as a vital tool to guide into the region of the high degree of isospin asymmetry and density. We take varieties of parameter sets of the RMF model to show the parametric dependence of the hyperon star properties. We add $ϕ_0$-meson to $σ$-$ω$-$ρ$ model. The effects of $ϕ_0$-meson on the equation of state and consequently on the maximum mass of the hyperon star are discussed. Due to the inclusion of $ϕ_0$-meson the threshold density of different hyperon production shift to higher density region. The effects of the hyperon-meson coupling constants on…
Inclusive $K^+$ and exclusive $K^+Y$ photoproduction on the deuteron are investigated theoretically. Modern hyperon-nucleon forces and a recently updated kaon photoproduction operator for the $γ+N\to K^++Y$ process are used. Sizable effects of the hyperon-nucleon final state interaction are found near the $K^+ΛN$ and $K^+ΣN$ thresholds in the inclusive reaction. Angular distributions for the exclusive process show clear $YN$ final state interaction effects in certain kinematic regions. Precise data especially for the inclusive process around the $K^+ΣN$ threshold would help to clarify the stre…
In this work we revisit the quantum hadrodynamics (QHD) formalism to investigate hyperonic and hybrid stars with hyperon-meson couplings fixed via broken SU(6) group, in favor of a more general flavor group SU(3). We also employ an additional channel, the strangeness-hidden $ϕ$ meson, which couples only to the hyperons. In hybrid stars, the quark phase is built with the SU(3) NJL model also with an additional vector channel in the Lagrangian. We found that within the models chosen the hyperon puzzle cannot be avoided by the quark-hadron phase transition, once the hyperon threshold always happe…
In relativistic ion collisions there are excellent opportunities to produce and investigate hyper-nuclei. We have systematically studied the formation of hypernuclear spectator residues in peripheral heavy-ion collisions with the transport DCM and UrQMD models. The hyperon capture was calculated within the potential and coalescence approaches. We demonstrate that even at the beam energies around and lower than the threshold for producing Lambda hyperons in binary nucleon-nucleon interactions a considerable amount of hypernuclei, including multi-strange ones, can be produced. This is important …
