Meson-baryon Vertices Research Articles

Standard model contribution to the electric dipole moment of the deuteron, 3H, and 3He nuclei

We calculate for the first time the electric dipole moment (EDM) of the deuteron, 3H, and 3He nuclei generated by the one-meson exchange CP-odd nuclear force in the standard model. The effective |ΔS| = 1 four-quark operators are matched to the |ΔS| = 1 standard model processes involving the CP phase of the Cabibbo-Kobayashi-Maskawa matrix at the electroweak scale and run down to the hadronic scale μ = 1 GeV according to the renormalization group evolution in the next-to-leading logarithmic order. At the hadronic scale, the hadron matrix elements are modeled in the factorization approach. We then obtain the one-meson (pion, eta meson, and kaon) exchange CP-odd nuclear force, which is the combination of the |ΔS| = 1 meson-baryon vertices which issue from the penguin operator and the hyperon-nucleon transition. From this CP-odd nuclear force, the nuclear EDM is calculated with the realistic Argonne v18 interaction and the CP-odd nuclear force using the Gaussian expansion method. It is found that the EDMs of light nuclear systems are of order O (10−31)e cm. We also estimate the standard model contribution to other hadronic CP violating observables such as the EDMs of 6Li, 9Be nuclei, and the atomic EDMs of 129Xe, 199Hg, 211Rn, and 225Ra generated through the nuclear Schiff moment. We then analyze the source of theoretical uncertainties and show some possible ways to overcome them.

Thermal properties of asymmetric nuclear matter

The thermal properties of asymmetric nuclear matter are investigated in a relativistic mean-field approach. We start from free-space $NN$ interactions and derive in-medium self-energies by the Dirac-Brueckner theory. By the density-dependent relativistic hadron procedure we derive in a self-consistent approach density-dependent meson-baryon vertices. At the mean-field level, we include isoscalar and isovector-scalar and vector interactions. The nuclear equation of state is investigated for a large range of total baryon densities up to the neutron star regime, the full range of asymmetries $\ensuremath{\xi}=Z/A$ from symmetric nuclear matter to pure neutron matter, and temperatures up to $T\ensuremath{\sim}100$ MeV. The isovector-scalar self-energies are found to modify strongly the thermal properties of asymmetric nuclear matter. A striking result is the change of phase transitions when isovector-scalar self-energies are included.

Combined large-Ncand heavy-quark operator analysis for the chiral Lagrangian with charmed baryons

The chiral $SU(3)$ Lagrangian with charmed baryons of spin $J^P=1/2^+$ and $J^P=3/2^+$ is analyzed. We consider all counter terms that are relevant at next-to-next-to-next-to-leading order (N$^3$LO) in a chiral extrapolation of the charmed baryon masses. At N$^2$LO we find 16 low-energy parameters. There are 3 mass parameters for the anti-triplet and the two sextet baryons, 6 parameters describing the meson-baryon vertices and 7 symmetry breaking parameters. The heavy-quark spin symmetry predicts four sum rules for the meson-baryon vertices and degenerate masses for the two baryon sextet fields. Here a large-$N_c$ operator analysis at NLO suggests the relevance of one further spin-symmetry breaking parameter. Going from N$^2$LO to N$^3$LO adds 17 chiral symmetry breaking parameters and 24 symmetry preserving parameters. For the leading symmetry conserving two-body counter terms involving two baryon fields and two Goldstone boson fields we find 36 terms. While the heavy-quark spin symmetry leads to $36-16=20$ sum rules, an expansion in $1/N_c$ at next-to-leading order (NLO) generates $36-7= 29$ parameter relations. A combined expansion leaves 3 unknown parameters only. For the symmetry breaking counter terms we find 17 terms, for which there are $17-9=8$ sum rules from the heavy-quark spin symmetry and $17-5=12 $ sum rules from a $1/N_c$ expansion at NLO.

The role of the Λ(1405) in the pp → pK+Λ(1405) reaction

We report a theoretical study of the pp → pK +Λ(1405) reaction, which was recently investigated at COSY-Julich by using a 3.65GeV/c circulating proton beam incident on an internal hydrogen target. The reaction is driven by single-kaon exchange, single-pion exchange, and single-rho exchange terms which have very different shapes due to the two-pole structure of the Λ(1405) and the presence of background terms. The shape for the sum of the three contributions, as well as the total cross-section, are consistent with present data within experimental and theoretical uncertainties, using reasonable form factors for the meson-baryon vertices.

Density functional theory for nuclei and hypernuclei

Nuclear matter and finite nuclei at extreme isospin are studied using the DDRH field theory. A relativistic energy density functional with density dependent meson–baryon vertex functionals, derived from the Dirac–Brueckner theory, is derived. Dynamical correlations from pairing interactions and core polarization are found to increase strongly when approaching the driplines. The above particle threshold core polarization gives rise to narrow Fano Resonances as a new mode of continuum excitation. This is accompanied by a strong reduction of mean-field configurations. Pygmy dipole resonances are found to provide a clear signature for neutron skins.

Correlation dynamics in dripline nuclei

The transition from mean-field to correlation dynamics is studied by nuclear many-body theory in nuclear matter and finite nuclei at extreme isospin. In-medium interactions in nuclear and hypernuclear matter are described by DDRH theory with density dependent meson–baryon vertex functionals. In ladder approximation, their structure is derived from Dirac–Brueckner theory. Relativistic mean-field results are presented ranging from nuclear matter over isotopic chains of nuclei to neutron stars. Dynamical correlations from pairing interactions and core polarization are found to increase strongly when approaching the driplines. This is accompanied by a strong reduction of mean-field configurations, as indeed observed in recent experiments. Anharmonicities in dipole excitations are investigated along isotopic chains including up to three phonon admixtures and using microscopic HFB quasiparticle input. The pygmy dipole resonance is found to provide a clear signature for neutron skins.

Correlation dynamics in dripline nuclei

The transition from mean-field to correlation dynamics is studied by nuclear many-body theory in nuclear matter and finite nuclei at extreme isospin. In-medium interactions in nuclear and hypernuclear matter are described by DDRH theory with density dependent meson–baryon vertex functionals. In ladder approximation, their structure is derived from Dirac–Brueckner theory. Relativistic mean-field results are presented ranging from nuclear matter over isotopic chains of nuclei to neutron stars. Dynamical correlations from pairing interactions and core polarization are found to increase strongly when approaching the driplines. This is accompanied by a strong reduction of mean-field configurations, as indeed observed in recent experiments. Anharmonicities in dipole excitations are investigated along isotopic chains including up to three phonon admixtures and using microscopic HFB quasiparticle input. The pygmy dipole resonance is found to provide a clear signature for neutron skins.

Relativistic σ-ω mean-field theory for hyperons from a quark model

We suggest a phenomenological description of hypernuclear \ensuremath{\sigma}-\ensuremath{\omega} Dirac mean-field theory, where the meson-baryon vertices are based on the quark model with relativistic corrections. While the model is shown to be in agreement with the \ensuremath{\sigma}-\ensuremath{\omega} model for regular nuclei, large tensor \ensuremath{\omega}YY couplings are derived for \ensuremath{\omega}-hyperon vertices. This coupling, which is negligible for nucleons, is capable of resolving the problem of the small spin-orbit interaction in \ensuremath{\Lambda} hypernuclei within the Dirac approach, as was recently shown independently by Jennings. Our model explains the available data. It can also be the basis for more systematic theoretical studies. Predictions are thus presented for \ensuremath{\Sigma} and \ensuremath{\Xi} hypernuclei. Further improvements of the model are discussed.

Analysis of the meson-baryon vertex in an infinite multiplet model based on the groupSL 6,C

We consider the meson-baryon vertex which is symmetric underSL6,C and project out the mesonic form factors of the baryon octet. These form factors are given in terms of integrals over algebraic functions of thirty-eight parameters. Seventeen integrations are performed with the help of group theory. The remaining twenty-one integrations cannot be done with analytic methods. Some analytic properties of the form factors are discussed.

Sum Rules for Coupling Constants in Exact and BrokenSU(6)W

The meson-baryon vertex and the decuplet decays are studied within the framework of the exact and the broken $\mathrm{SU}{(6)}_{W}$ group. The breaking is provided by a $W$-spin scalar spurion transforming like the $I=0$, $Y=0$ member of the 35-dimensional adjoint representation of $\mathrm{SU}{(6)}_{W}$. Twenty-one sum rules are obtained in the broken symmetry. One of these directly relates the ($p,p{\ensuremath{\pi}}^{0}$) and (${N}^{*++},p{\ensuremath{\pi}}^{+}$) couplings and yields a decay width $\ensuremath{\Gamma}({N}^{*++}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{+})=70$ MeV. Another relates the vertices ($Y_{1}^{}{}_{}{}^{*+},\ensuremath{\Lambda}{\ensuremath{\pi}}^{+}$) and ($Y_{1}^{}{}_{}{}^{*+},{\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{0}$), which seems to agree with the latest experiments on $Y_{1}^{}{}_{}{}^{*}$ decays. One more relation among the observable decuplet decays is the Gupta-Singh sum rule, which is very well satisfied experimentally. Some predictions of exact $\mathrm{SU}{(6)}_{W}$ seem to disagree with experiment. It is concluded that in the context of three-point functions the predictions of the broken $\mathrm{SU}{(6)}_{W}$ group are in very good agreement with experiments.

Relativistic Formulation of theSU(6)Symmetry Scheme

A relativistic formulation of the $\mathrm{SU}(6)$ symmetry scheme is presented, starting with the basic assumption that the fields corresponding to elementary particles are tensors of $M(12)$ [or $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{U}(12)$ or $\mathrm{SU}(12)\mathfrak{L}$]. In particular a mixed second-rank tensor and a totally symmetric third-rank tensor are associated with the meson and baryon fields, respectively. It is shown that if these fields are required to satisfy prescribed free-field equations of motion, then one is led to a particle supermultiplet structure which corresponds to the 35\ensuremath{\bigoplus}1 and 56-dimensional representations of $\mathrm{SU}(6)$ for the mesons and baryons. It is also shown that the spin-dependent and $\mathrm{SU}(3)$-spin-dependent mass splittings can be included in the theory and that solutions in terms of physical particle fields can be obtained. Effective trilinear meson-meson and meson-baryon vertex functions, using these solutions and an interaction Lagrangian which is invariant under $M(12)$, are calculated in the lowest order perturbation. We would like to note especially the following results: (a) From the known pion-nucleon coupling constant, the width of the pion-nucleon (3,3) resonance is calculated to be 94 MeV. (b) The ratio of the magnetic form factors for the neutron and proton is -⅔ for all momentum transfers and ${\ensuremath{\mu}}_{P}=(1+\frac{2{M}_{P}}{{m}_{\ensuremath{\rho}}})$ nuclear magnetons. (c) The charge form factor of the neutron is zero for all momentum transfers.

Hyperon-pair production

The production of YY pairs in pp collisions is shown to be consistent with a peripheral model based on K* exchange, if the SA parity is even. The result is not sensitive to the form of the meson-baryon vertices for comparable values of the coupling constants.