Vector Meson Couplings Research Articles

Heavy baryon–light vector meson couplings in QCD

The strong coupling constants of heavy baryons with light vector mesons are calculated in the framework of the light cone QCD sum rules using the most general form of the interpolating currents for the heavy baryons. It is shown that the sextet–sextet, sextet–antitriplet and antitriplet–antitriplet transitions are described by one invariant function for each class of transitions. The values of the electric and magnetic coupling constants for these transitions are obtained.

Parity-violating asymmetry in theHe3(n⃗,p)H3reaction

The longitudinal asymmetry induced by parity-violating (PV) components in the nucleon-nucleon potential is studied in the charge-exchange reaction $^{3}\mathrm{He}$($\mathrm{nP\vec},p$)$^{3}\mathrm{H}$ at vanishing incident neutron energies. An expression for the PV observable is derived in terms of $T$-matrix elements for transitions from the ${}^{2S+1}{L}_{J}={}^{1}{S}_{0}$ and ${}^{3}{S}_{1}$ states in the incoming $n$-$^{3}\mathrm{He}$ channel to states with $J=0$ and 1 in the outgoing $p$-$^{3}\mathrm{H}$ channel. The $T$-matrix elements involving PV transitions are obtained in first-order perturbation theory in the hadronic weak-interaction potential, while those connecting states of the same parity are derived from solutions of the strong-interaction Hamiltonian with the hyperspherical-harmonics method. The coupled-channel nature of the scattering problem is fully accounted for. Results are obtained corresponding to realistic or chiral two- and three-nucleon strong-interaction potentials in combination with either the DDH or pionless EFT model for the weak-interaction potential. The asymmetries, predicted with PV pion and vector-meson coupling constants corresponding (essentially) to the DDH ``best values'' set, range from --9.44 to --2.48 in units of ${10}^{\ensuremath{-}8}$, depending on the input strong-interaction Hamiltonian. This large model dependence is a consequence of cancellations between long-range (pion) and short-range (vector-meson) contributions and is of course sensitive to the assumed values for the PV coupling constants.

Hybrid Neutron Stars Based on a Modified PNJL Model

We discuss a three-flavor Nambu--Jona-Lasinio (NJL) type quantum field theoretical approach to the quark matter equation of state (EoS) with scalar diquark condensate, isoscalar vector mean field and Kobayashi-Maskawa-'t Hooft (KMT) determinant interaction. While often the diquark and vector meson couplings are considered as free parameters, we will fix them here to their values according to the Fierz transformation of a one-gluon exchange interaction. In order to estimate the effect of a possible change in the vacuum pressure of the gluon sector at finite baryon density we exploit a recent modification of the Polyakov-loop NJL (mPNJL) model which introduces a parametric density dependence of the Polyakov-loop potential also at T=0, thus being relevant for compact star physics. We use a Dirac-Brueckner-Hartree-Fock (DBHF) EoS for the hadronic matter phase and discuss results for mass-radius relationships following from a solution of the TOV equations for such a hybrid EoS in the context of observational constraints from selected objects.

Form factors of vector and axial-vector mesons in holographic D4-D8 model

We calculate elastic and non-elastic electromagnetic form factors for vector and axial-vector mesons in the holographic D4-D8 brane model. We obtain the mass spectrum and Regge trajectories for these particles. From the elastic form factors we extract the electric radius, the magnetic and quadrupole moments. Form factors for transverse and longitudinal polarizations are also obtained. We find superconvergence sum rules for the vector and axial-vector meson couplings that determine the asymptotic behavior of the form factors at large momentum transfer. Our results show good agreement with other holographic models and QCD.

Non-local mean field effect on nuclei near [formula omitted] sub-shell

Evolutions of single-particle energies and Z=64 sub-shell along the isotonic chain of N=82 are investigated in the density dependent relativistic Hartree–Fock (DDRHF) theory in comparison with other commonly used mean field models such as Skyrme HF, Gogny HFB and density dependent relativistic Hartree model (DDRMF). The pairing is treated in the BCS scheme, except for Gogny HFB. It is pointed out that DDRHF reproduces well characteristic features of experimental Z-dependence of both spin–orbit and pseudo-spin–orbit splittings around the sub-shell closure Z=64. Non-local exchange terms of the isoscalar σ and ω couplings play dominant roles in the enhancements of the spin–orbit splitting of proton 2d states, which is the key ingredient to give the Z=64 sub-shell closure properly. On the other hand, the π and ρ tensor contributions for the spin–orbit splitting cancel each other and the net effect becomes rather small. The enhancement of the sub-shell gaps towards Z=64 is studied by the DDRHF, for which the local terms of the scalar and vector meson couplings are found to be important.

Physical results from2+1flavor domain wall QCD and SU(2) chiral perturbation theory

We have simulated QCD using 2+1 flavors of domain wall quarks on a $(2.74 {\rm fm})^3$ volume with an inverse lattice scale of $a^{-1} = 1.729(28)$ GeV. The up and down (light) quarks are degenerate in our calculations and we have used four values for the ratio of light quark masses to the strange (heavy) quark mass in our simulations: 0.217, 0.350, 0.617 and 0.884. We have measured pseudoscalar meson masses and decay constants, the kaon bag parameter $B_K$ and vector meson couplings. We have used SU(2) chiral perturbation theory, which assumes only the up and down quark masses are small, and SU(3) chiral perturbation theory to extrapolate to the physical values for the light quark masses. While next-to-leading order formulae from both approaches fit our data for light quarks, we find the higher order corrections for SU(3) very large, making such fits unreliable. We also find that SU(3) does not fit our data when the quark masses are near the physical strange quark mass. Thus, we rely on SU(2) chiral perturbation theory for accurate results. We use the masses of the $\Omega$ baryon, and the $\pi$ and $K$ mesons to set the lattice scale and determine the quark masses. We then find $f_\pi = 124.1(3.6)_{\rm stat}(6.9)_{\rm syst} {\rm MeV}$, $f_K = 149.6(3.6)_{\rm stat}(6.3)_{\rm syst} {\rm MeV}$ and $f_K/f_\pi = 1.205(0.018)_{\rm stat}(0.062)_{\rm syst}$. Using non-perturbative renormalization to relate lattice regularized quark masses to RI-MOM masses, and perturbation theory to relate these to $\bar{\rm MS}$ we find $ m_{ud}^{\bar{\rm MS}}(2 {\rm GeV}) = 3.72(0.16)_{\rm stat}(0.33)_{\rm ren}(0.18)_{\rm syst} {\rm MeV}$ and $m_{s}^{\bar{\rm MS}}(2 {\rm GeV}) = 107.3(4.4)_{\rm stat}(9.7)_{\rm ren}(4.9)_{\rm syst} {\rm MeV}$.

The chiral model of Sakai-Sugimoto at finite baryon density

In the context of holographic QCD we analyze Sakai-Sugimoto's chiral model at finite baryon density and zero temperature. The baryon number density is introduced through compact D4 wrapping S^4 at the tip of D8-\bar{D8}. Each baryon acts as a chiral point-like source distributed uniformly over R^3, and leads a non-vanishing U(1)_V potential on the brane. For fixed baryon charge density n_B we analyze the bulk energy density and pressure using the canonical formalism. The baryonic matter with point like sources is always in the spontaneously broken phase of chiral symmetry, whatever the density. The point-like nature of the sources and large N_c cause the matter to be repulsive as all baryon interactions are omega mediated. Through the induced DBI action on D8-\bar{D8}, we study the effects of the fixed baryon charge density n_B on the pion and vector meson masses and couplings. Issues related to vector dominance in matter in the context of holographic QCD are also discussed.

Baryon-Number-Induced Chern-Simons Couplings of Vector and Axial-Vector Mesons in Holographic QCD

We show that holographic models of QCD predict the presence of a Chern-Simons coupling between vector and axial-vector mesons at finite baryon density. In the Anti de Sitter/Conformal Field Theory dictionary, the coefficient of this coupling is proportional to the baryon number density and is fixed uniquely in the five-dimensional holographic dual by anomalies in the flavor currents. For the lightest mesons, the coupling mixes transverse rho and a1 polarization states. At sufficiently large baryon number densities, it produces an instability, which causes the rho and a1 mesons to condense in a state breaking both rotational and translational invariance.

Isospin violation in the vector form factors of the nucleon

A quantitative understanding of isospin violation is an increasingly important ingredient for the extraction of the nucleon's strange vector form factors from experimental data. We calculate the isospin violating electric and magnetic form factors in chiral perturbation theory to leading and next-to-leading order respectively, and we extract the low-energy constants from resonance saturation. Uncertainties are dominated largely by limitations in the current knowledge of some vector meson couplings. The resulting bounds on isospin violation are sufficiently precise to be of value to on-going experimental studies of the strange form factors.

On the Couplings of Vector Mesons in AdS/QCD

We address, in the AdS/CFT context, the issue of the universality of the couplings of the rho meson to other hadrons. Exploring some models, we find that generically the rho-dominance prediction f_\rho g_{\rho H H}=m_\rho^2 does not hold, and that g_{\rho H H} is not independent of the hadron H. However, we prove that, in any model within the AdS/QCD context, there are two limiting regimes where the g_{\rho H H}, along with the couplings of all excited vector mesons as well, become H-independent: (1) when H is created by an operator of large dimension, and (2) when H is a highly-excited hadron. We also find a sector of a particular model where universality for the rho coupling is exact. Still, in none of these cases need it be true that f_\rho g_\rho=m_\rho^2, although we find empirically that the relation does hold approximately (up to a factor of order two) within the models we have studied.

Current algebra derivation of temperature dependence of hadron couplings with currents

The vector and the axial-vector meson couplings with the vector and the axial-vector currents respectively at finite temperature have been obtained in Ref. \cite{Mallik} by calculating all the relevant one-loop Feynman graphs with vertices obtained from the effective chiral Lagrangian. On the other hand, the same couplings were also derived in Ref.\cite{Ioffe1} by applying the method of current algebra and the hypothesis of partial conservation of axial-vector current (PCAC). The latter method appears to miss certain terms; in the case of the vector meson coupling with the vector current, for example, a term containing the $\rho\omega\pi$ coupling is missed. A similar situation would also appear for the nucleon coupling with the nucleon current. In this note we resolve these differences.

Radiative decays involving [formula omitted] and [formula omitted] and mixing between low and high mass scalar mesons

We analyze the experimental data for ϕ → f 0 ( 980 ) γ , ϕ → a 0 ( 980 ) γ , f 0 ( 980 ) → γ γ and a 0 ( 980 ) → γ γ decay widths in a framework where f 0 ( 980 ) and a 0 ( 980 ) are assumed to be mainly q q q ¯ q ¯ low mass scalar mesons and mixed with q q ¯ high mass scalar mesons. Applied the vector meson dominance model (VDM), these decays amplitudes are expressed by coupling parameters B describing the S ( q q q ¯ q ¯ scalar meson)– V (vector meson)– V (vector meson) coupling and B ′ describing the S ′ ( q q ¯ scalar meson)– V– V coupling. Adopting the magnitudes for B and B ′ as ∼ 2.8 GeV −1 and ∼ 12 GeV −1 , respectively, the mixing angle between a 0 ( 980 ) and a 0 ( 1450 ) as ∼ 9 ° , and the mixing parameter λ 01 causing the mixing between I = 0 q q q ¯ q ¯ state and q q ¯ state as ∼ 0.24 GeV 2 , we can interpret these experimental data, consistently.

Parity-violating interaction effects in thenpsystem

We investigate parity-violating observables in the $np$ system, including the longitudinal asymmetry and neutron-spin rotation in $\stackrel{P\vec}{n}p$ elastic scattering, the photon asymmetry in $\stackrel{P\vec}{n}p$ radiative capture, and the asymmetries in deuteron photodisintegration $d(\stackrel{P\vec}{\ensuremath{\gamma}},n)p$ in the threshold region and electrodisintegration $d(\stackrel{P\vec}{e},{e}^{\ensuremath{'}})np$ in quasielastic kinematics. To have an estimate of the model dependence for the various predictions, a number of different, latest-generation strong-interaction potentials---Argonne ${v}_{18}$, Bonn 2000, and Nijmegen I---are used in combination with a weak-interaction potential consisting of $\ensuremath{\pi}$-, $\ensuremath{\rho}$-, and $\ensuremath{\omega}$-meson exchanges---the Desplanques-Donoghue-Holstein (DDH) model. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials are solved in both configuration and momentum space. The issue of electromagnetic current conservation is examined carefully. We find large cancellations between the asymmetries induced by the parity-violating interactions and those arising from the associated pion-exchange currents. In the $\stackrel{P\vec}{n}p$ capture, the model dependence is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant ${E}_{1}$ matrix elements. In quasielastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by $\ensuremath{\gamma}\text{\ensuremath{-}}Z$ interference on individual nucleons. These two experiments, then, provide clean probes of different aspects of weak-interaction physics associated with parity violation in the $np$ system. Finally, we find that the neutron-spin rotation in $\stackrel{P\vec}{n}p$ elastic scattering and asymmetry in deuteron disintegration by circularly polarized photons exhibit significant sensitivity both to the values used for the weak vector-meson couplings in the DDH model and to the input strong-interaction potential adopted in the calculation. This reinforces the conclusion that these short-ranged meson couplings are not in themselves physical observables; rather, the parity-violating mixings are the physically relevant parameters.

Vector meson couplings to vector and tensor currents in extended NJL quark model

A simple explanation of the dynamic properties of vector mesons is given in the framework of extended Nambu - Jona-Lasinio quark model. New mass relations among the hadron vector resonances are derived. The results of this approach are in good accordance with the QCD sum rules, the lattice calculations and the experimental data.

Ward identities,B→ρ form factors and |Vub|

The exclusive FCNC beauty semileptonic decay B-> \rho is studied using Ward identities in a general vector meson dominance framework, predicting vector meson couplings involved. The long distance contributions are discussed which results to obtain form factors and |V_ub|. A detailed comparison is given with other approaches.

Lattice calculation of vector meson couplings to the vector and tensor currents using chirally improved fermions

We present a quenched lattice calculation of $f_V^\perp/f_V$, the coupling of vector mesons to the tensor current normalized by the vector meson decay constant. The chirally improved lattice Dirac operator, which allows us to reach small quark masses, is used. We put emphasis on analyzing the quark mass dependence of $f_V^\perp/f_V$ and find only a rather weak dependence. Our results at the $\rho$ and $\phi$ masses agree well with QCD sum rule calculations and those from previous lattice studies.

Vector Meson Couplings to Nucleons and Backward ρ and ω Production**The project supported in part by the Knowledge Innovation Project of the Chinese Academy of Sciences under Grant No. KJCX2-SWN02.

Data on the production of vector mesons ρ and ω in the backward direction via nucleon exchange are investigated. A better understanding of these data is achieved than hitherto, albeit at a semi-quantitative level. This is achieved partly by using more up-to-date values for the vector couplings and partly by using more precise theoretical formalism. In view of this we conclude that the data do provide a useful constraint on the couplings.

Folding model study ofα−pscattering: Systematics of elastic scattering, effective interaction, and inelastic excitation ofN*resonances

For a description of elastic and inelastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering exciting ${N}^{*}$ resonances optical potentials and transition potentials were derived by folding nucleon and nucleus mass densities with a variable range effective interaction. For elastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering in forward direction, a reasonable description of essentially all data has been obtained from low energies up to the GeV region. Also, $\ensuremath{\alpha}$ scattering from ${}^{4}\mathrm{He}$ and ${}^{12}\mathrm{C}$ is quite well described with potentials, which indicate that the used folding method is a valid approach for the systems in question. The strong energy dependence of the deduced potentials can be accounted for by a sum of scalar and vector meson-exchange potentials and a soft Pomeron-exchange contribution. The scalar meson-exchange potential falls off rapidly with energy and has a large radius in agreement with theoretical predictions. Consistent with the flavor SU(3) quark model, the vector-meson coupling is rather weak in the central potential, but is strong in the spin-orbit potential, for which a soft Pomeron contribution is negligible. The differences between the deduced $\ensuremath{\alpha}\ensuremath{-}p$ and nucleon-nucleon $(\mathrm{NN})$ potentials are understood; further, an excellent description of the energy dependence of the s-wave $\mathrm{NN}$ amplitudes is obtained in the folding model framework. Distorted wave Born approximation calculations for inelastic $\ensuremath{\alpha}\ensuremath{-}p$ scattering show a t-dependence of the $L=0$ cross section consistent with empirical form factors. Absolute yields for excitation of the resonances ${P}_{11}(1440),$ ${D}_{13}(1520)$ and ${F}_{15}(1680)$ were calculated, using resonance shapes from $\ensuremath{\pi}\ensuremath{-}N$ scattering. A quantitative description of the data at ${E}_{\ensuremath{\alpha}}=4.2\mathrm{GeV}$ is obtained using fluid-dynamical transition densities and strengths exhausting large fractions of scalar energy weighted sum rules. The rather pure scalar (non-spin-isospin-flip) character of these excitations and the observed cross sections are in severe conflict with the constituent quark model. Finally, a prediction is made for $p\ensuremath{-}\ensuremath{\alpha}$ scattering at an incident energy of ${E}_{p}=2.2\mathrm{GeV},$ which yields strongly increased cross sections for ${N}^{*}$ excitations.

Coupling of the light vector meson to the vector and to the tensor current

We present results for the coupling of the light vector mesons to the tensor current, relative to the standard vector meson decay constants. From an (a)-improved lattice study, performed at three values of the lattice spacing in the quenched approximation, our final values (in the continuum limit), in the MS-bar scheme at μ = 2 GeV, are: fρT/fρ = 0.72(2)(+2−0), fK*T/fK* = 0.74(2), fϕT/fϕ = 0.76(1).

Nuclear and neutron star radii

We investigate the correlation between nuclear neutron radii and the radius of neutron stars. We use a well-established hadronic SU(3) model based on chiral symmetry that naturally includes non-linear vector meson and scalar meson - vector meson couplings. The relative strengths of the couplings modify the nuclear isospin-dependent interactions. We study the dependence of nuclear and neutron star radii on the coupling strengths. The relevance of the results for parity-violating electron-nucleus scattering and the URCA process in neutron stars is discussed.