We review the status as regards the existence of three- and four-body bound states made of neutrons and $Λ$ hyperons. For interesting cases, the coupling to neutral baryonic systems made of charged particles of different strangeness has been addressed. There are strong arguments showing that the $Λnn$ system has no bound states. $ΛΛnn$ strong stable states are not favored by our current knowledge of the strangeness $-1$ and $-2$ baryon-baryon interactions. However, a possible $Ξ^- t$ quasibound state decaying to $ΛΛnn$ might exist in nature. Similarly, there is a broad agreement about the nonexistence of $ΛΛn$ bound states. However, the coupling to $ΞNN$ states opens the door to a resonance above the $ΛΛn$ threshold.
Analytic expressions are given for the baryonic, electric and strangeness chemical potentials which explicitly show the importance of various terms. Simple scaling relations connecting these chemical potentials are found. Applications to particle ratios and to fluctuations and related thermal properties such as the isothermal compressibility kappaT are illustrated. A possible divergence of kappaT is discussed.
We derive a simple relation between strangeness neutrality and baryon-strangeness correlations. In heavy-ion collisions, the former is a consequence of quark number conservation of the strong interactions while the latter are sensitive probes of the character of QCD matter. This relation allows us to directly extract baryon-strangeness correlations from the strangeness chemical potential at strangeness neutrality. The explicit calculations are performed within a low energy theory of QCD with 2+1 dynamical quark flavors at finite temperature and density. Non-perturbative quark and hadron fluctu…
The ratios of off-diagonal to diagonal conserved charge susceptibilities e.g., chi_{BS}/chi_{S}, chi_{QS}/chi_{S}, related to the quark flavor susceptibilities, have proven to be discerning probes of the flavor carrying degrees of freedom in hot strongly interacting matter. Various constraining relations between the different susceptibilities are derived based on the Gell-Mann-Nishijima formula and the assumption of isospin symmetry. Using generic models of deconfined matter and results form lattice QCD, it is demonstrated that the flavor carrying degrees of freedom at a temperature above 1.5T…
Recent developments of chiral effective field theory (ChEFT) applications to nuclear and neutron matter are summarized, with special emphasis on a (non-perturbative) extension using functional renormalisation group methods. Topics include: nuclear thermodynamics, extrapolations to dense baryonic matter and constraints from neutron star observables. Hyperon-nuclear interactions derived from SU(3) will be discussed with reference to the "hyperon puzzle" in neutron star matter.
We study the thermodynamical properties of compressed baryonic matter with strangeness within non-relativistic energy density functional models with a particular emphasis on possible phase transitions found earlier for a simple $n,p,e,Λ$-mixture. The aim of the paper is twofold: I) examining the phase structure of the complete system, including the full baryonic octet and II) testing the sensitivity of the results to the model parameters. We find that, associated to the onset of the different hyperonic families, up to three separate strangeness-driven phase transitions may occur. Consequently,…
Since the incident nuclei in heavy-ion collisions do not carry strangeness, the global net strangeness of the detected hadrons has to vanish. We show that there is an intimate relation between strangeness neutrality and baryon-strangeness correlations. In the context of heavy-ion collisions, the former is a consequence of quark number conservation of the strong interactions while the latter are sensitive probes of the character of QCD matter. We investigate the sensitivity of baryon-strangeness correlations on the freeze-out conditions of heavy-ion collisions by studying their dependence on te…
We compare relativistic mean field models with their low density expansion counterparts used to mimic non-relativistic models by consistently expanding the baryonic scalar density in powers of the baryonic number density up to ${\cal O}(13/3)$, which goes two orders beyond the order considered in previous works. We show that, due to the non-trivial density dependence of the Dirac mass, the convergence of the expansion is very slow, and the validity of the non-relativistic approximation {\bf is} questionable even at subsaturation densities. In order to analyze the roles played by strangeness an…
We present a strangeness-neutral equation of state for QCD that exhibits critical behavior and matches lattice QCD results for the Taylor-expanded thermodynamic variables up to fourth-order in $μ_B/T$. It is compatible with the SMASH hadronic transport approach and has a range of temperatures and baryonic chemical potentials relevant for phase II of the Beam Energy Scan at RHIC. We provide an updated version of the software BES-EoS, which produces an equation of state for QCD that includes a critical point in the 3D Ising model universality class. This new version also includes isentropic trej…
Kaon production in pion-nucleon collisions in nuclear matter is studied in the resonance model. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states. These vector and scalar potentials were calculated using the quark-meson coupling (QMC) model. The in-medium kaon production cross sections in pion-nucleon interactions for reaction channels with $Λ$ and $Σ$ hyperons in the final state were calculated at the baryonic densities appro…
We calculate a resummed equation of state with lattice QCD simulations at imaginary chemical potentials. This work presents a generalization of the scheme introduced in 2102.06660 to the case of non-zero $μ_S$, focusing on the line of strangeness neutrality. We present results up to $μ_B/T \leq 3.5$ on the strangeness neutral line $\left\langle S \right\rangle = 0$ in the temperature range $130 \rm{MeV} \leq T \leq 280 \rm{MeV}$. We also extrapolate the finite baryon density equation of state to small non-zero values of the strangeness-to-baryon ratio $R=\left\langle S \right\rangle / \left\la…
The Beam Energy Scan program at the Relativistic Heavy Ion Collider (RHIC) is searching for the QCD critical point. The main signal for the critical point is the kurtosis of the distribution of proton yields obtained on an event-by-event basis where one expects a peak at the critical point. However, its exact behavior is still an open question due to out-of-equilibrium effects and uncertainty in the equation of state. Here we use a simplistic hydrodynamic model that enforces strangeness-neutrality, selecting trajectories that pass close to the critical point. We vary the initial conditions to …
Results of the analysis of the MiniBooNE experiment data for the neutral current elastic neutrino scattering off the $CH_{2}$ target with the NuWro Monte Carlo generator are presented. Inclusion in the NuWro the two body current contribution leads to the axial mass value $M_A = 1.10^{+0.13}_{-0.15}$ GeV consistent with the older evaluations based on the neutrino-deuteron scattering data. The strange quark contribution to the nucleon spin is estimated with the value $g_A^s = -0.4^{+0.5}_{-0.3}$.
Fluctuations of conserved charges such as baryon number, electric charge and strangeness may provide a test for completeness of states in lattice QCD for three light flavors. We elaborate on the idea that the corresponding susceptibilities can be saturated with excited baryonic states with an underlying quark-diquark structure with a linearly confining interaction. Using Polyakov-loop correlators we show that in the static limit, the quark-diquark potential coincides with the quark-antiquark potential in marked agreement with recent lattice studies. We thus study in a quark-diquark model the b…
We construct a model for dense matter based on low-density nuclear matter properties that exhibits a chiral phase transition and that includes strangeness through hyperonic degrees of freedom. Empirical constraints from nuclear matter alone allow for various scenarios, from a strong first-order chiral transition at relatively low densities through a weaker transition at higher densities, even up to a smooth crossover not far beyond the edge of the allowed range. The model parameters can be chosen such that at asymptotically large densities the chirally restored phase contains strangeness and t…
Our current knowledge of the baryon--baryon interaction suggests that the dineutron $(n,n)$ and its strange analogue $(n,Λ)$ are unstable. In contrast, the situation is more favorable for the strange three-body system $(n,n,Λ)$, and even better for the four-body system $T\equiv (n,n,Λ,Λ)$ with strangeness $-2$, which is likely to be stable under spontaneous dissociation. The recent models of the hyperon-nucleon and hyperon-hyperon interactions suggest that the stability of the $(n,n,Λ)$ and $T$ is possible within the uncertainties of our knowledge of the baryon-baryon interactions. This new nu…
We have studied the $N^*(2120)$, $Δ^*(1940)$, and the possible $Σ^*(1380)$ resonances in the $γp \to K^+ Λ(1520)$, $pp \to n K^+ Σ(1385)$, and $Λp \to Λp π^0$ reactions within the resonance model and the effective Lagrangian approach. It is shown that when the contributions from these baryonic states were considered, the current experimental measurement could be well reproduced. In addition, we also demonstrate that the angular distributions provide direct information of these reactions, which could be useful for the investigation of those states and may be tested by future experiments.
We construct an equation of state for Quantum Chromodynamics (QCD) at finite temperature and chemical potentials for baryon number $B$, electric charge $Q$ and strangeness $S$. We use the Taylor expansion method, up to the fourth power for the chemical potentials. This requires the knowledge of all diagonal and non-diagonal $BQS$ correlators up to fourth order: these results recently became available from lattice QCD simulations, albeit only at a finite lattice spacing $N_t=12$. We smoothly merge these results to the Hadron Resonance Gas (HRG) model, to be able to reach temperatures as low as …
Within the framework of the improved isospin dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K$^{0,+}$, $Λ$ and $Σ^{-,0,+}$) production in heavy-ion collisions near threshold energies is investigated systematically, in which the strange particles are considered to be mainly produced by the inelastic collisions of baryon-baryon and pion-baryon. The collisions in the region of supra-saturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. The total multiplicities as functions of incident ener…
Above a critical matter density the propagating modes of the neutral kaon system are essentially eigenstates of strangeness, but below it they are almost complete eigenstates of CP. We estimate the real and imaginary parts of the energies of these modes and their mixing at all densities up to nuclear matter density $2\times 10^{14}$ g/cm$^3$. In a heavy ion collision the strong interactions create eigenstates of strangeness, and these propagate adiabatically until the density has fallen to the critical value, whereupon the system undergoes a sudden transition to (near) eigenstates of CP. We es…
The extraction of the nucleon's strangeness axial charge, Delta_s, from inclusive, quasielastic neutral current neutrino cross sections is studied within the framework of the plane-wave impulse approximation. We find that the value of Delta_s can depend significantly on the choice of nuclear model used in analyzing the quasielastic cross section. This model-dependence may be reduced by one order of magnitude when Delta_s is extracted from the ratio of total proton to neutron yields. We apply this analysis to the interpretation of low-energy neutrino cross sections and arrive at a nuclear theor…
Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the s-wave meson-baryon resonances in the strangeness S=-3 and negative parity sector. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2+ octet of the nucleon and the 3/2+ decuplet of the…
The effects of strong color electric fields (SCF) on the baryon production at RHIC are studied in the framework of HIJING/BB (v2.0) model. The particle species dependence of nuclear modification factors (NMF) are analyzed for Au+Au collisions at 200A GeV. A doubling of the string tension leading to a modification of the strangeness suppression according to Schwinger mechanism is shown to provide an alternate explanation to coalescence models for the interpretation of the observed baryon and meson production at moderate $p_T$ and results in a predicted enhancement in the (multi)strange (anti)hy…
We explore the effects of strangeness and $Δ$ resonance in baryonic matter and compact stars within the relativistic-mean-field (RMF) models. The covariant density functional PKDD is adopted for $N$-$N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $Δ$-meson couplings. In light of the recent observations of GW170817 with the dimensionless combined tidal deformability $197 \leq \barΛ\leq 720$, we find it is essential to include the $Δ$ resonances in compact …
We formulate a family of equations of state for Quantum Chromodynamics that exhibit critical features and obey the charge conservation conditions present in heavy-ion collisions (HICs). This construction utilizes the first-principle Lattice QCD (LQCD) results up to $\mathcal{O}(μ_B^4)$ by matching the Taylor coefficients at each order. The criticality of the equation of state (EoS) is implemented based on the well-established principle of universal scaling behavior, where QCD belongs to the 3D Ising Model universality class. The critical point can be placed in a range of temperature and baryon…
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）
We construct the QCD equation of state at finite chemical potentials including net baryon, electric charge, and strangeness based on the results of lattice QCD simulations and the hadron resonance gas model. The situation of strangeness neutrality and a fixed charge-to-baryon ratio, which resembles that of heavy nuclei, is considered for the application to relativistic heavy-ion collisions. This increases the values of baryon chemical potential compared to the case of vanishing strangeness and electric charge chemical potentials, modifying the fireball trajectory in the phase diagram. We perfo…
Neutrino processes caused by the neutral current are studied in octet baryon matter. Previous confusion about the baryonic matrix elements of the neutral current interaction is excluded, and a correct table for them improved by consideration of the proton spin problem is presented instead.
We study $S$-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons using the lowest order chiral Lagrangian. In the S=1 sector, we find an attractive interaction in the $ΔK$ channel with I=1 while it is repulsive for I=2. The attractive interaction leads to a pole in the second Riemann sheet of the complex plane and is manifested as a large strength in the scattering amplitude close to the $ΔK$ threshold, which is not the case for I=2. We use the unitarized coupled channel approach to also investigate all the other possible values of strangeness and isospin. We find tw…
We report on the latests developments in the field of baryonic resonances generated from the meson-baryon interaction in coupled channels using a chiral unitary approach. The collection of resonances found in different strangeness and isospin sectors can be classified into SU(3) multiplets. The Lambda(1405) emerges as containing the effect of two poles of the scattering amplitude and various reactions that might preferentially select one or the other pole are discussed.
