Baryon Octet Research Articles

Parity doublet model for baryon octets: Diquark classifications and mass hierarchy based on the quark-line diagram

Parity doublet model for baryon octets: Diquark classifications and mass hierarchy based on the quark-line diagram

A closer look at the Yukawa interaction from a symmetry group perspective

Abstract I investigate the use of the SU(3) Clebsch–Gordan coefficients in light of the relations of completeness and closure. I show that in the case of αV = F/(F + D) ≠ 1, there is an additional interaction: the exchange of a ρ meson between a Λ and a Σ0 hyperon that only affects the symmetric coupling. I then calculate these additional coupling constants and show that this recovers the completeness and closure of the SU(3) Clebsch–Gordan coefficients for all values of αV. Besides, it increases the symmetry of the theory, now we can group the baryon octet into four doublets. Finally, I add the new coupling constants to study numerical results in the hyperon onset in dense nuclear matter assuming αV as a free parameter.

Data driven isospin analysis of timelike octet baryons electromagnetic form factors and charmonium decay into baryon-anti-baryon

Inspired by the recent precise data, we perform model-independently an isospin decomposition of the timelike octet baryons electromagnetic form factors. As noted in our previous work, the relative magnitude of isoscalar and isovector component is determined with the input of data on various isospin channels. Herein we further assert that their relative phase can be constraint by the phase difference of oscillatory modulation of effective form factors between isospin channels. The framework is extended to analyze the data of differential cross sections and applied to the form factors of nucleon and hyperons with detail and isospin non-conservation of charmonium decay into baryon-anti-baryon as well. We address that isospin analysis is meaningful when the isospin broken scale is compared to or smaller than the uncertainties of data.

Four-body baryonic [formula omitted] decays

LHCb has recently reported the first observation of a four-body baryonic B→B1B¯1′B2B¯2′ decay, where B1B¯1′ and B2B¯2′ represent the two pairs of octet baryon states. In our classification, the measured B¯0→pp¯pp¯ decay is a tree dominated process via internal W-boson emission, whose branching fraction is explained as small as 2.2×10−8. We investigate for the first time the phenomenology of other tree and penguin dominated B→B1B¯1′B2B¯2′ decays, and predict the presence of a double threshold effect, manifested as two peaks around mB1B¯1′∼mB1+mB¯1′ and mB2B¯2′∼mB2+mB¯2′ in the invariant mass spectra of B1B¯1′ and B2B¯2′, respectively. Moreover, we predict the following branching fractions: B(B−→np¯pp¯)=(1.7−0.2+0.4±0.1−0.4+0.7)×10−7, B(B−→Λp¯pp¯)=(7.4−0.2+0.6±0.03−2.6+3.6)×10−7, and B(B¯s0→ΛΛ¯pp¯)=(1.9−0.1+0.3±0.01−0.6+1.1)×10−7, which are accessible to experimental facilities.

Octet and decuplet baryon σ terms and mass decompositions

We present a comprehensive analysis of the SU(3) octet and decuplet baryon masses and $\sigma$-terms using high-precision lattice QCD data and chiral SU(3) effective theory with finite range regularization. The effects of various systematic uncertainties, including from the scale setting of the lattice data and the regularization prescriptions, are quantified. We find the pion-nucleon and strange nucleon $\sigma$-terms to be $\sigma_{\pi N} = 44(3)(3)$ MeV and $\sigma_{N s} = 50(6)(1)$ MeV, respectively. The results provide constraints on the energy-momentum tensor mass decompositions of the SU(3) octet and decuplet baryons, where we find the trace anomaly and quark/gluon energies decrease for strange baryons due to their larger strange $\sigma$-terms.

Low-energy constants in the chiral Lagrangian with baryon octet and decuplet fields from Lattice QCD data on CLS ensembles

We perform an analysis of Lattice QCD data on baryon octet and decuplet masses based on the chiral SU(3) Lagrangian. Low-energy constants (LEC) are adjusted to describe baryon masses from a large set of CLS ensembles, where finite-box and discretization effects are considered. The set is successfully compared against previous Lattice QCD data from ensembles generated with distinct QCD actions by the ETMC, QCDSF-UKQCD and HSC groups. Discretization effects are modelled by the use of action and lattice-scale dependent leading orders LEC, where uniform values are imposed in the limit of vanishing lattice scales. From the CLS data set we extract a pion-nucleon sigma term, sigma _{pi N}= 58.7(1.2) MeV, compatible with its empirical value.

Baryon and meson masses in the Nambu–Jona-Lasinio model: A Bayesian approach

We investigate the capabilities of the Nambu--Jona-Lasinio model to describe and reproduce fundamental vacuum properties of Quantum Chromodynamics, notably the hadronic spectrum. Mesons are described as quark-antiquark bound states at the level of the random phase approximation of the Bethe-Salpeter equation, while baryons are characterized as quark-diquark bound states within the static approximation of the Faddeev equation. Within a Bayesian framework, we constrain the model by phenomenologically known quantities and study the implications on its parameters and predictions in vacuum, as well as the correlations between the two. We find that within our framework, the vacuum masses of mesons and baryons can be reasonably well reproduced. Scalar diquarks need to be significantly bound in order to correctly reproduce the masses of the baryon octet, therefore enforcing values of the scalar diquark coupling larger than what is suggested by the canonical Fierz values. These findings could have important implications on the phenomenology of strongly-interacting matter at high temperature and density as well as of compact star physics.

Axial transition form factors of octet baryons in the perturbative chiral quark model

We study the axial transition form factors $G_A^{B\to B'}(Q^2)$ as well as the axial charges $g_A^{B\to B'}$ of the octet baryons in the perturbative chiral quark model~(PCQM) with including both the ground and excited states in the intermediate quark propagators. The PCQM results on the $G_A^{B\to B'}(Q^2)$ and the $g_A^{B\to B'}$ are found in good agreement with the existing experimental data and the lattice-QCD values. The study figures out that the $G_A^{B\to B'}(Q^2)$ for all transitions behave in the dipolelike form, which is dominantly caused by the three-quark core. The meson cloud with the ground-state quark propagator also plays an extremely important role but results in a flat contribution. The excited-state quark propagator contributing to the $G_A^{B\to B'}(Q^2)$ could be regarded as the higher order correction and it is very limited.

Quark orbital angular momentum of ground-state octet baryons

Here we study the quark orbital angular momentum of the ground octet baryons employing an extended chiral constituent quark model, within which the baryon wave functions are taken to be superposition of the traditional $qqq$ and the $qqqq\overline{q}$ higher Fock components. Coupling between the two configurations is estimated using the $^{3}P_{0}$ quark-antiquark creation mechanism, and the corresponding coupling strength is determined by fitting the sea flavor asymmetry of the nucleon. The obtained numerical results show that the quark angular momentum of the nucleon, $\mathrm{\ensuremath{\Sigma}}, \mathrm{\ensuremath{\Lambda}}$, and $\mathrm{\ensuremath{\Xi}}$ hyperons, are in the range 0.10--0.30. In addition, the quark angular momentum of all the hyperons are a little bit smaller than that of the nucleon. And the octet baryons spin fractions taken by the intrinsic quark orbital angular momentum could be up to $60%$ in present model.

Effect of nucleon coupling constants on the mass radius ratio of proto neutron star PSR J0737-3039A

The effect of the nucleon coupling constants on the mass radius ratio (further, the surface gravitational redshift) of proto neutron star (PNS) PSR J0737-3039A is examined with relativistic mean field theory in consideration of a baryon octet. Here, five sets of nucleon coupling constants DD-MEI, GL85, GL97, GM1 and NL2 are used. The PNS’s temperature is assumed to be [Formula: see text] MeV and the mass the PNS PSR J0737-3039A is chosen as [Formula: see text]. The radius and the mass radius ratio of the PNS PSR J0737-3039A calculated by the five groups of nucleon coupling constants above are [Formula: see text] km and [Formula: see text]/km, respectively. The surface gravitational redshift [Formula: see text] of the PNS PSR J0737-3039A calculated from the above five groups of nucleon coupling constants is [Formula: see text].

The chiral Lagrangian with three flavors and large-N_c sum rules

We reconsider the chiral Lagrangian with three-flavor baryon fields. A systematic analysis of all low-energy constants (LEC) that contribute to the axial-vector and pseudoscalar currents in the baryon octet and decuplet fields at next-to-leading order in the inverse number of colors (1/N_c) of QCD is performed. We study the correlation function consisting of axial-vector and scalar currents as well. While there are 4 LEC relevant at leading chiral order, the number of relevant LEC at subleading order is 23. For those a leading order large-N_c analysis predicts 3 and 18 sum rules respectively. At the next accuracy level the number of sum rules is reduced to 2 and 8. Our results are illustrated by a tree-level analysis of available axial-vector coupling constants and strong decay widths of the baryon decuplet states.

Gravitational form factors of the baryon octet with flavor SU(3) symmetry breaking

We investigate the gravitational form factors of the baryon octet within the framework of the SU(3) chiral quark-soliton model, considering the effects of flavor SU(3) symmetry breaking, and with the corresponding energy-momentum tensor distributions. We examine the effects of flavor SU(3) symmetry breaking to the mass, angular momentum, pressure, and shear force distributions of the baryon octet. We first find that a heavier baryon is energetically more compact than a lighter one. For the spin distributions of the baryon octet, they are properly normalized to their spins and are decomposed into the flavor-singlet axial charge and the orbital angular momentum even when the flavor SU(3) symmetry is broken. While the effects of the flavor SU(3) symmetry breaking differently contribute to the angular momentum distributions for the octet baryons, they are found to be rather small. The spin and orbital angular momentum almost equally contribute to the angular momentum distributions for the octet baryons. We also estimate the effects of the flavor SU(3) symmetry breaking to the pressure and shear force distributions. Interestingly, even if we include the effects of the SU(3) flavor symmetry breaking, then the shear force distributions are kept to be positive over $r$. It indicates that the Polyakov and Schweitzer local stability condition is kept to be intact with the flavor SU(3) symmetry broken. Lastly, we discuss how much the gravitational form factors vary with the effects of flavor SU(3) symmetry breaking considered.

Fragmentation functions for [formula omitted] using neural networks

We present a determination of fragmentation functions (FFs) for the octet baryon Ξ−/Ξ¯+ from data for single inclusive electron-positron annihilation. Our parametrization in this QCD analysis is provided in terms of a Neural Network (NN). We determine fragmentation functions for Ξ−/Ξ¯+ at next-to-leading order and for the first time at next-to-next-to-leading order in perturbative QCD. We discuss the improvement of higher-order QCD corrections, the quality of fit, and the comparison of our theoretical results with the fitted datasets. As an application of our new set of fragmentation functions, named SHKS22, we present predictions for Ξ−/Ξ¯+ baryon production in proton-proton collisions at the LHC experiments.

The Non-Linear Derivative (NLD) model for the in-medium hyperons & antihyperons dynamics

The in-medium properties of hyperons and antihyperons are studied with the Non-Linear Derivative (NLD) model and focus is made on the momentum dependence of strangeness optical potentials[1]. The NLD model is based on the Relativistic Mean Field (RMF) approximation to Relativistic Hadrodynamics (RHD) approach of nuclear systems, but it incorporates an explicit momentum dependence of mean-fields. The extension of the NLD model to the baryon and antibaryon octet is based on SU(6) and G-parity arguments. It is demonstrated that with a proper choice of momentum cut-offs, the Λ and Σ optical potentials are consistent with recent studies of the chiral effective field theory and Ξ optical potentials are consistent with Lattice-QCD calculations, over a wide momentum region. We also present NLD predictions for the in-medium momentum dependence of antiΛ, antiΣ and antiΞ hyperons. This work is important for future experimental studies, like CBM, PANDA at FAIR and is relevant to nuclear astrophysics as well.

Quark spin content of SU(3) light and singly heavy baryons

We investigate the quark spin content of the SU(3) baryon octet, decuplet, antitriplet, and sextet in a pion mean-field approach or the chiral quark-soliton model, considering the $1/N_c$ rotational corrections and SU(3) symmetry breaking effects. We compare the present results with those from various theoretical works and lattice QCD.

Contact interaction analysis of octet baryon axial-vector and pseudoscalar form factors

Octet baryon axial, induced pseudoscalar, and pseudoscalar form factors are computed using a symmetry-preserving treatment of a vector$\,\times\,$vector contact interaction (SCI), thereby unifying them with an array of other baryon properties and analogous treatments of semileptonic decays of pseudoscalar mesons. The baryons are treated as quark--plus--interacting-diquark bound states, whose structure is obtained by solving a Poincar\'e-covariant Faddeev equation. The approach is marked by algebraic simplicity, involves no free parameters, and since it is symmetry preserving, all consequences of partial conservation of the axial current are manifest. It is found that SCI results are consistent with only small violations of SU$(3)$-flavour symmetry, an outcome which may be understood as a dynamical consequence of emergent hadron mass. The spin-flavour structure of the Poincar\'e-covariant baryon wave functions is expressed in the presence of both flavour-antitriplet scalar diquarks and flavour-sextet axialvector diquarks and plays a key role in determining all form factors. Considering neutral axial currents, SCI predictions for the flavour separation of octet baryon axial charges and, therefrom, values for the associated SU$(3)$ singlet, triplet, and octet axial charges are obtained. The results indicate that at the hadron scale, $\zeta_{\cal H}$, valence degrees-of-freedom carry roughly 50% of an octet baryon's total spin. Since there are no other degrees-of-freedom at $\zeta_{\cal H}$, the remainder may be associated with quark+diquark orbital angular momentum.

Massive relativistic compact stars from SU(3) symmetric quark models

We construct a set of hyperonic equations of state (EoS) by assuming SU(3) symmetry within the baryon octet and by using a covariant density functional (CDF) theory approach. The low-density regions of our EoS are constrained by terrestrial experiments, while the high-density regime is modeled by systematically varying the nuclear matter skewness coefficient Qsat and the symmetry energy slope Lsym. The sensitivity of the EoS predictions is explored in terms of z parameter of the SU(3) symmetric model that modifies the meson-hyperon coupling constants away from their SU(6) symmetric values. Our results show that model EoS based on our approach can support static Tolman-Oppenheimer-Volkof (TOV) masses in the range 2.3-2.5M⊙ in the large-Qsat and small-z regime, however, such stars contain only a trace amount of hyperons compared to SU(6) models. We also construct uniformly rotating Keplerian configurations for our model EoS for which the masses of stellar sequences may reach up to 3.0M⊙. These results are used to explore the systematic dependence of the ratio of maximum masses of rotating and static stars, the lower bound on the rotational frequency of the models that will allow secondary masses in the gravitational waves events to be compact stars with M2≲3.0M⊙ and the strangeness fraction on the model parameters. We conclude that very massive stellar models can be, in principle, constructed within the SU(3) symmetric model, however, they are nucleonic-like as their strangeness fraction drops below 3%.

In-medium Λ isospin impurity from charge symmetry breaking in the Λ4H−Λ4He mirror hypernuclei

The $\Lambda$ separation energies in the mirror hypernuclei ${_{\Lambda}^4}{\rm H}-{_{\Lambda}^4}{\rm He}$ exhibit large charge symmetry breaking (CSB). Analyzing this CSB within pionless effective field theory while using partially conserved baryon-baryon SU(3) flavor symmetry, we deduce a $\Lambda -\Sigma^0$ induced in-medium admixture amplitude ${\cal A}_{I=1}\approx 1.5\%$ in the dominantly isospin $I=0$ $\Lambda$ hyperon. Our results confirm the free-space value ${\cal A}^{(0)}_{I=1}$ inferred directly within the SU(3) baryon octet by Dalitz and von-Hippel in 1964 and reaffirmed in a recent QCD+QED lattice calculation. Furthermore, exploring the consequences of SU(3) flavor symmetry on the $\Lambda$-nucleon interaction, we find that CSB is expected to impact the $S=1$ and $S=0$ spin channels in opposite directions, with the latter dominating by an order of magnitude. These observations explain a recent deduction of $\Lambda$-nucleon CSB strengths.

Equivalent SU(3)f approaches for two-body anti-triplet charmed baryon decays

For the two-body Bc → BM decays, where Bc denotes the anti-triplet charm baryon and B(M) the octet baryon (meson), there exist two theoretical studies based on the SU(3) flavor [SU(3)f] symmetry. One is the irreducible SU(3)f approach (IRA). In the irreducible SU(3)f representation, the effective Hamiltonian related to the initial and final states forms the amplitudes for Bc → BM. The other is the topological-diagram approach (TDA), where the W-boson emission and W-boson exchange topologies are drawn and parameterized for the decays. As required by the group theoretical consideration, we present the same number of the IRA and TDA amplitudes. We can hence relate the two kinds of the amplitudes, and demonstrate the equivalence of the two SU(3)f approaches. We find a specific W-boson exchange topology only contributing to {Xi}_c^0 →BM. Denoted by EM, it plays a key role in explaining mathcal{B} ( {Xi}_c^0 → Λ0 {K}_S^0 , Σ0 {K}_S^0 , Σ+K−). We consider that {Lambda}_c^{+} → nπ+ and {Lambda}_c^{+} → pπ0 proceed through the constructive and destructive interfering effects, respectively, which leads to mathcal{B} ( {Lambda}_c^{+} → nπ+) » mathcal{B} ( {Lambda}_c^{+} → pπ0) in agreement with the data. With the exact and broken SU(3)f symmetries, we predict the branching fractions of Bc→BM to be tested by future measurements.

Proto-Neutron Star Matter

In this paper, we explore the properties of proto-neutron star matter. The relativistic finite-temperature Green function formalism is used to derive the equations which determine the properties of such matter. The calculations are performed for the relativistic non-linear mean-filed theory, where different combinations of lepton number and entropy have been investigated. All particles of the baryon octet as well as all electrically charged states of the Δ isobar have been included in the calculations. The presence of all these particles is shown to be extremely temperature (entropy) dependent, which should have important consequences for the evolution of proto-neutron stars to neutron stars as well as the behavior of neutron stars in compact star mergers.