arXiv subjects

Th. A. Rijken

Publications and source records attributed to Th. A. Rijken.

At least 37 records · Page 2Linked to original sources

arXiv2014

Hyperon mixing and universal many-body repulsion in neutron stars

A multi-pomeron exchange potential (MPP) is proposed as a model for the universal many-body repulsion in baryonic systems on the basis of the Extended Soft Core (ESC) bryon-baryon interaction. The strength of MPP is determined by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The interaction in $ΛN$ channels is shown to reproduce well the experimental $Λ$ binding energies. The equation of state (EoS) in neutron matter with hyperon mixing is obtained including the MPP contribution, and mass-radius relations of neutron stars are derived. It is shown that the maximum mass can be larger than the observed one $2M_{\odot}$ even in the case of including hyperon mixing on the basis of model-parameters determined by terrestrial experiments.

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arXiv2014

Three-body structure of the $nnΛ$ system with $ΛN-ΣN$ coupling

The structure of the three-body $nnΛ$ system, which has been observed recently by the HypHI collaboration, is investigated taking $ΛN-ΣN$ coupling explicitly into account. The $YN$ and $NN$ interactions employed in this work reproduce the binding energies of $^3_Λ$H, $^4_Λ$H and $^4_Λ$He. We do not find any $^3_Λn$ bound state, which contradicts the interpretation of the data reported by the HypHI collaboration.

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arXiv2008

Light $Ξ$ hypernuclei in four-body cluster models

Detailed structure calculations in $^{\: 12}_{Ξ^-}$Be, $^{\: 5}_{Ξ^-}$H, $^{\: 9}_{Ξ^-}$Li, $^{\: 7}_{Ξ^-}$H and $^{\:10}_{Ξ^-}$Li are performed within the framework of the microscopic two-, three- and four-body cluster models using the Gaussian Expansion Method.

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arXiv2006

Four-body structure of $^7_Λ$Li and $ΛN$ spin-dependent interaction

Two spin-doublet states of %$3/2^+$-$1/2^+$ and $7/2^+$-$5/2^+$ in $^7_Λ$Li are studied on the basis of the $α+Λ+n+p$ four-body model. We employ the two-body interactions which reproduce the observed properties of any subsystems composed of $αN$, $αΛ$ and $αNN$, and $αΛN$. Furthermore, the $ΛN$ interaction is adjusted so as to reproduce the $0^+$-$1^+$ splitting of in $^4_Λ$H. The calculated energy splittings of $3/2^+$-$1/2^+$ and $7/2^+$-$5/2^+$ states in $^7_Λ$Li are 0.69 MeV and 0.46 MeV, which are in good agreement with the resent observed data. The spin-dependent components of the $ΛN$ interaction are discussed.

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arXiv2006

Extended-soft-core baryon-baryon model III. $S=-2$ hyperon-hyperon/nucleon interaction

This paper presents the Extended-Soft-Core (ESC) potentials ESC04a-d for baryon-baryon channels with total strangeness $S=-2$. For these channels no experimental scattering data exist, and alsothe information from hypernuclei is very limited.The potential models for $S=-2$ are based on SU(3) extensions of potential models for the $S=0,-1$ sectors, which are fitted to experimental data. Flavor su(3)-symmetry is broken 'kinematically'by the masses of the baryons and the mesons.Moreover, in ESC04a,b aldo the coupling constants are broken, albeit in a well defined way using the $^3P_0$ quark-antiquark pair creation model as a guidance. But the fit to the S=0 and $S=-1$ sectors provides the necessary constraints to fix all free parameters.Therefore, the potentials for the $S=-2$ sectors do not contain additional free parameters, which situation is similar to the soft-core one-boson-exchange NSC97-models. Various properties of the potentials are illustrated by giving results for scattering lengths, bound states, phase-parameters, and total cross sections. The features of $Ξ$-hypernuclei predicted by ESC04d are studied on the basis of the G-matrix approach.

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arXiv2006

The nucleon-sigma coupling constant in QCD Sum Rules

The external-field QCD Sum Rules method is used to evaluate the coupling constant of the light isoscalar-scalar meson (``$σ$'' or ε) to the nucleon. The contributions that come from the excited nucleon states and the response of the continuum threshold to the external field are calculated. The obtained value of the coupling constant is compatible with the large value required in one-boson exchange potential models of the two-nucleon interaction.

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arXiv2006

Scalar-Meson - Baryon Coupling Constants in QCD Sum Rules

The external-field QCD Sum Rules method is used to evaluate the coupling constants of the light-isoscalar scalar meson (``σ'' or ε) to the Λ, Σ, and Ξbaryons. It is shown that these coupling constants as calculated from QCD Sum Rules are consistent with SU(3)-flavor relations, which leads to a determination of the F/(F+D) ratio of the scalar octet assuming ideal mixing: we find α_s \equiv F/(F+D)=0.55. The coupling constants with SU(3) breaking effects are also discussed.

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arXiv2006

Extended-soft-core Baryon-Baryon Model I. Nucleon-Nucleon Scattering (ESC04) Extended-soft-core Baryon-Baryon Model I. Nucleon-Nucleon Scattering (ESC04)

The NN results are presented from the extended-soft-core (ESC) interactions. They cosist of local- and non-local-potentials due to (i) one-boson-exchange (OBE), pseudo-scalar-, vector-, scalar-, and axial-vector-nonets, (ii) diffractive exchanges, (iii) two-pseudoscalar-exchange, and (iv) meson-pair-exchange (MPE). Fits to the pp- and np-data for 0 < T(lab) < 350 MeV have typical χ^2/Ndata= 1.15. Used are less than 20 parameters, which are coupling constants and cut-off masses. The couplings follow rather closely the pattern predicted by the quark-pair-creation model. As a result the 11 OBE-couplings are rather constrained, i.e. quasi-free. The deuteron binding energy and several NN scattering lengths are fitted at the same time.

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arXiv2006

Extended-soft-core Baryon-Baryon Model II. Hyperon-Nucleon Interaction

The YN results are presented from the Extended-soft-core (ESC) interactions. They consist of local- and non-local-potentials due to (i) One-boson-exchange (OBE), with pseudoscalar-, vector-, scalar-, and axial-vector-nonets, (ii) Diffractive exchanges, (iii) Two-pseudoscalar exchange, and (iv) Meson-pair-exchange (MPE). This model, called ESC04, describes NN and YN in a unified way using broken flavor SU(3)-symmetry. Novel ingredients are the inclusion of (i) the axial-vector-mesons, (ii) a zero in the scalar- and axial-vector meson form factors. We describe simultaneous fits to the NN- and YN-data, using four options in the ESC-model. Very good fits were obtained. G-matrix calculations with these four options are also reported. The obtained well depths (U_Λ, U_Σ, U_Ξ) reveal distinct features of ESC04a-d. The ΛΛ-interactions are demonstrated to be consistent with the observed data of_{ΛΛ}^6He. The possible three-body effects are investigated by considering phenomenologically the changes of the vector-meson masses in a nuclear medium.

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arXiv2005

Soft-core meson-baryon interactions. I. One-hadron-exchange potentials

The Nijmegen soft-core model for the pseudoscalar-meson baryon interaction is derived, analogous to the Nijmegen NN and YN models. The interaction Hamiltonians are defined and the resulting amplitudes for one-meson-exchange and one-baryon-exchange in momentum space are given for the general mass case. The partial wave projection is carried through and explicit expressions for the momentum space partial wave meson-baryon potentials are presented.

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arXiv2005

Soft-core meson-baryon interactions. II. $πN$ and $K^+ N$ scattering

The $πN$ potential includes the t-channel exchanges of the scalar-mesons $σ$ and f_0, vector-meson $ρ$, tensor-mesons f_2 and f_2' and the Pomeron as well as the s- and u-channel exchanges of the nucleon N and the resonances $Δ$, Roper and S_{11}. These resonances are not generated dynamically. We consider them as, at least partially, genuine three-quark states and we treat them in the same way as the nucleon. The latter two resonances were needed to find the proper behavior of the phase shifts at higher energies in the corresponding partial waves. The soft-core $πN$-model gives an excellent fit to the empirical $πN$ S- and P-wave phase shifts up to T_{lab}=600 MeV. Also the scattering lengths have been reproduced well and the soft-pion theorems for low-energy $πN$ scattering are satisfied. The soft-core model for the $K^+ N$ interaction is an SU_f(3)-extension of the soft-core $πN$-model. The $K^+ N$ potential includes the t-channel exchanges of the scalar-mesons a_0, $σ$ and f_0, vector-mesons $ρ$, $ω$ and $ϕ$, tensor-mesons a_2, f_2 and f_2' and the Pomeron as well as u-channel exchanges of the hyperons $Λ$ and $Σ$. The fit to the empirical $K^+ N$ S-, P- and D-wave phase shifts up to T_{lab}=600 MeV is reasonable and certainly reflects the present state of the art. Since the various $K^+ N$ phase shift analyses are not very consistent, also scattering observables are compared with the soft-core $K^+ N$-model. A good agreement for the total and differential cross sections as well as the polarizations is found.

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arXiv2002

ESC NN-Potentials in Momentum Space. I. PS-PS Exchange Potentials

A momentum space representation is derived for the Nijmegen Extended-Soft-Core (ESC) interactions. The partial wave projection of this representation is carried through, in principle for Two-Meson-Exchange (TME) in general. Explicit results for the momentum space partial wave NN-potentials from PS-PS-Exchange are given.

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arXiv2002

ESC NN-Potentials in Momentum Space. II. Meson-Pair Exchange Potentials

The partial wave projection of the Nijmegen soft-core potential model for Meson-Pair-Exchange (MPE) for NN-scattering in momentum space is presented. Here, nucleon-nucleon momentum space MPE-potentials are NN-interactions where either one or both nucleons contains a meson-pair vertex. Dynamically, the meson-pair vertices can be viewed as describing in an effective way (part of) the effects of heavy-meson exchange and meson-nucleon resonances. From the point of view of ``duality,'' these two kinds of contribution are roughly equivalent. Part of the MPE-vertices can be found in the chiral-invariant phenomenological Lagrangians that have a basis in spontaneous broken chiral symmetry. It is shown that the MPE-interactions are a very important component of the nuclear force, which indeed enables a very succesful description of the low and medium energy NN-data. Here we present a precise fit to the NN-data with the extended-soft-core (ESC) model containing OBE-, PS-PS-, and MPE-potentials. An excellent description of the NN-data for $T_{Lab} \leq 350$ MeV is presented and discussed. Phase shifts are given and a $χ^2_{p.d.p.} = 1.15$ is reached.

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arXiv1999

Soft-core baryon-baryon potentials for the complete baryon octet

SU(3) symmetry relations on the recently constructed hyperon-nucleon potentials are used to develop potential models for all possible baryon-baryon interaction channels. The main focus is on the interaction channels with total strangeness S=-2, -3, and -4, for which no experimental data exist yet. The potential models for these channels are based on SU(3) extensions of potential models for the S=0 and S=-1 sectors, which are fitted to experimental data. Although the SU(3) symmetry is not taken to be exact, the S=0 and S=-1 sectors still provide the necessary constraints to fix all free parameters. The potentials for the S=-2, -3, and -4 sectors, therefore, do not contain any additional free parameters, which makes them the first models of this kind. Various properties of the potentials are illustrated by giving results for scattering lengths, bound states, and total cross sections.

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arXiv1998

Soft-core hyperon-nucleon potentials

A new Nijmegen soft-core OBE potential model is presented for the low-energy YN interactions. Besides the results for the fit to the scattering data, which largely defines the model, we also present some applications to hypernuclear systems using the G-matrix method. An important innovation with respect to the original soft-core potential is the assignment of the cut-off masses for the baryon-baryon-meson (BBM) vertices in accordance with broken SU(3)$_F$, which serves to connect the NN and the YN channels. As a novel feature, we allow for medium strong breaking of the coupling constants, using the $^3P_0$ model with a Gell-Mann--Okubo hypercharge breaking for the BBM coupling. We present six hyperon-nucleon potentials which describe the available YN cross section data equally well, but which exhibit some differences on a more detailed level. The differences are constructed such that the models encompass a range of scattering lengths in the $ΣN$ and $ΛN$ channels. For the scalar-meson mixing angle we obtained values $θ_S=37$ to 40 degrees, which points to almost ideal mixing angles for the scalar $q\bar{q}$ states. The G-matrix results indicate that the remarkably different spin-spin terms of the six potentials appear specifically in the energy spectra of $Λ$ hypernuclei.

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arXiv1996

Meson-baryon coupling constants from a chiral-invariant SU(3) Lagrangian and application to NN scattering

We present a chiral-invariant meson-baryon Lagrangian which describes the interactions of the baryon octet with the lowest-mass meson nonets. The nonlinear realization of the chiral symmetry generates pair-meson interaction vertices. The corresponding pair-meson coupling constants can all be expressed in terms of the meson-nucleon-nucleon pseudovector, scalar, and vector coupling constants, and their corresponding $F/(F+D)$ ratios, and for which empirical estimates are given. We show that it is possible to construct an NN potential of reasonable quality satisfying these theoretical and empirical constraints.

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arXiv1996

Soft two-meson-exchange nucleon-nucleon potentials. I. Planar and crossed-box diagrams

Pion-meson-exchange nucleon-nucleon potentials are derived for two nucleons in the intermediate states. The mesons we include are (i) pseudoscalar mesons: $π, η, η'$; (ii) vector mesons: $ρ, ω, ϕ$; (iii) scalar mesons: $a_{0}(980), \varepsilon(760), f_{0}(975)$; and (iv) the $J=0$ contribution from the Pomeron. Strong dynamical pair suppression is assumed, and at the nucleon-nucleon-meson vertices Gaussian form factors are incorporated into the relativistic two-body framework using a dispersion representation for the pion- and meson-exchange amplitudes. The Fourier transformations are performed using factorization techniques for the energy denominators. The potentials are first calculated in the adiabatic approximation to all planar and crossed three-dimensional momentum-space $π$-meson diagrams. Next, we calculate the $1/M$ corrections.

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arXiv1996

Soft two-meson-exchange nucleon-nucleon potentials. II. One-pair and two-pair diagrams

Two-meson-exchange nucleon-nucleon potentials are derived where either one or both nucleons contains a pair vertex. Physically, the meson-pair vertices are meant to describe in an effective way (part of) the effects of heavy-meson exchange and meson-nucleon resonances. {}From the point of view of ``duality,'' these two kinds of contribution are roughly equivalent. The various possibilities for meson pairs coupling to the nucleon are inspired by the chiral-invariant phenomenological Lagrangians that have appeared in the literature. The coupling constants are fixed using the linear $σ$ model. We show that the inclusion of these two-meson exchanges gives a significant improvement over a potential model including only the standard one-boson exchanges.

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