Weak magnetic field induced corrections to effective coupling constants describing light vector mesons mixings and vector meson dominance (VMD) are derived. The magnetic field must be weak with respect to an effective quark mass $M^*$ such that: $eB_0/{M^*}^2< 1$ or $eB_0/{M^*}^2<<1$.For that, a flavor SU(2) quark-quark interaction due to non perturbative one gluon exchange is considered. By means of methods usually applied to the Nambu Jona Lasinio (NJL) and Global Color Models (GCM), leading light vector/axial mesons couplings to a background electromagnetic field are derived. The corresponding effective coupling constants are resolved in the structureless mesons and longwavelength limits. Some of the resulting coupling constants are redefined such as to become magnetic field induced corrections to vector or axial mesons couplings. Due to the approximated chiral symmetry of the model, light axial mesons mixings induced by the magnetic field are also obtained. Some numerical estimates are presented for the coupling constants and for some of the corresponding momentum dependent vertices. The contributions of the induced VMD and vector mesons mixing couplings for the low momentum pion electromagnetic form factor and for the (off shell) charge symmetry violation potential at the constituent quark level are estimated. The relative overall weak magnetic field-induced anisotropic corrections are of the order of $(eB_0/{M^*}^2)^n$, where $n=2$ or $n=1$ respectively.
The axial strange form factor $F^s_A$ of the nucleon is assumed to be dominated at low momentum transfer by the isoscalar axial vector mesons $f_1(1285)$ and $f_1(1420)$. The importance of the $a_0πN$-triangular vertex correction is demonstrated.
We consider chiral perturbation theory with an explicit broad $σ$-meson and study its contribution to the scalar form factors of the pion and the nucleon. Our goal is to learn more about resonance saturation in the scalar sector.
We discuss the properties of vector mesons, in particular the rho^0, in the context of the Hidden Local Symmetry (HLS) model. This provides a unified framework to study several aspects of the low energy QCD sector. Firstly, we show that in the HLS model the physical photon is massless, without requiring off field diagonalization. We then demonstrate the equivalence of HLS and the two existing representations of vector meson dominance, VMD1 and VMD2, at both tree level and one loop order. Finally the S matrix pole position is shown to provide a model and process independent means of specifying …
We review the current status of rho-omega mixing and discuss its implication for our understanding of charge-symmetry breaking. In order to place this work in context we also review the photon-hadron coupling within the framework of vector meson dominance. This leads naturally to a discussion of the electromagnetic form-factor of the pion and of nuclear shadowing.
The axial form factor plays a crucial role in quasielastic neutrino-nucleus scattering, but the error of the theoretical cross section due to uncertainties of $G_A$ remains to be established. Reversely, the extraction of $G_A$ from the neutrino nucleus cross section suffers from large systematic errors due to nuclear model dependencies, while the use of single parameter dipole fits underestimates the errors and prevents an identification of the relevant kinematics for this determination. We propose to use a generalized axial-vector-meson-dominance (AVMD) in conjunction with large-$N_c$ and hig…
In this work, I studied the spectrum of scalar mesons and axial-vector mesons via Dyson-Schwinger equation and Bethe-Salpeter equation approach in the rainbow-ladder approximation. An interaction model with a repulsive term added to the one used for the pseudoscalar and vector mesons is proposed. My results are consistent with the experiment data and other model results, which shows that this interaction model is effective for all the heavy, heavy-light, and light scalar and axial-vector mesons.
Aspects of Scalar Meson Dominance in semi- and non-leptonic weak pseudoscalar meson decays are shortly discussed on the basis of the Quark-Level Linear Sigma Model.
A model is developed for electromagnetic form factor of the pion. One-loop corrections are included in the linear sigma-model. The rho-meson contribution is added in an extended VMD model. The form factor, calculated without fitting parameters, is in a good agreement with experiment for space-like and time-like photon momenta. Loop corrections to the two-pion hadronic contribution a^{(had, π)}_μto the muon anomalous magnetic moment are calculated. The optimal value of the sigma-meson mass appears to be close to the rho-meson mass.
The dispersive representation of axial anomaly leads to the anomaly sum rules (ASRs), exact nonperturbative relations in QCD. The analytical continuation of the ASRs to the time-like region is performed. The transition form factors of $π^0$, $η$ and $η'$ mesons in this region are calculated. A good agreement with the available experimental data is found. Based on the ASRs, we have provided the foundations for the vector meson dominance model in these processes.
Unusual constituent quark axial current couplings to light vector mesons, $ρ$ and $ω$, are derived in the vacuum and under weak magnetic field by considering a quark-antiquark interaction mediated by a non perturbative gluon exchange. Similarly, light axial mesons are found to couple anomalously with the constituent quark vector current. These interactions are of the type of the Wess-Zumino-Witten terms, being strongly anisotropic and dependent on the vector (or axial) meson polarization. They also provide axial (vector) form factors for the vector (axial) mesons and are quite small, suppresse…
We discuss the phenomenology of the axial-vector mesons within a three-flavour Linear Sigma Model containing scalar, pseudoscalar, vector and axial-vector degrees of freedom.
The effect of axial meson exchange on extraction of proton electromagnetic form factors in $ep$ scattering is calculated. Taking as an example $f_1(1285)$ meson exchange, it is quantitatively shown how it affects Rosenbluth and polarization transfer methods. The contribution of an axial meson is negligible in comparison with the traditional box-type two photon exchange and could not be responsible for difference of form factors extracted by different techniques. However, results support the idea that meson exchange could explain deviation of individual polarizations.
The meson cloud distributions in $r$-space are extracted from the nucleon electromagnetic and axial form factors which are derived in the perturbative chiral quark model. The theoretical results indicate that the electric charge and axial charge distributions of the three-quark core are the same, the magnetic charge distributions of the meson cloud and three-quark core are more or less in the same region and peak at distances of around 2 $\rm GeV^{-1}$, but the axial charge meson cloud distributes mainly inside the three-quark core.
Phenomenological multigauge model of neutrino-nucleon interaction based on chiral symmetry of strong interactions and vector/pseudovector meson dominance model is suggested. It was shown that within the framework of the model the constant of neutron beta decay is formed by meson masses and parameters of the hadronization of fundamental vector bosons. Then, quasi elastic (anti)neutrino-nucleon scattering processes have been investigated and it was found that weak nucleon form factor $G_A(Q^2)$ considered as multipole expansion multiplied on pQCD asymptotes is in a good agreement with experiment…
Vector-Meson-Dominance model contribution to $π^0 \to 4γ$ is calculated. The result confirms old estimates that this contribution is much smaller than the purely electromagnetic photon spliting graph contribution calculated earlier.
We show that nucleon electromagnetic structure functions of deep inelastic scattering in Regge-Gribov limit (fixed Q-squared, asymptotically large 1/x and s) can be well described in the two-component (soft + hard) approach. In the concrete model elaborated by authors, the soft part of the virtual photon-nucleon scattering is given by the vector meson dominance, with taking into account the radial excitations of the rho-meson and nondiagonal transitions in meson-nucleon interactions. The hard part is calculated by using the dipole factorization, i.e., the process is considered as the dissociat…
Extending previous work we study the constraints of QCD sum rules on mass and width of light vector and axial-vector mesons in vacuum and in a medium with finite nuclear density. For the latter case especially the effect of nuclear pions leading to vector-axial-vector mixing is included in the analysis.
We discuss the pion and nucleon form factors and generalized form factors within the large-Nc approach in the space-like region. We estimate their theoretical uncertainties through the use of the half-width rule, amounting to taking the half-width of the resonances as the deviation of their mass parameters. The approach embodies the meson dominance of form factors and the high-energy constraints from perturbative QCD. We compare the results with the available experimental data and lattice simulations. The meson-dominance form factors are generally comparable to the available experimental data …
A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the $ωρπ$ strong coupling. This coupling decreases with increasing $T$ and vanishes at the critical temperature, a likely signal for quark deconfinement. This is then used in the Vector Meson Dominance (VMD) expression for the $π^0 \to γγ$ amplitude, which is also found to vanish at the critical temperature, as expected. This result supports the validity of VMD at $T \neq 0$. However, if VMD would not hold at finite temperature, then there is no prediction for the $π^0 \to γγ$ amplitude.
Encouraged by a recent observation of the B_c^+ -> B_s^0 + pi^+ decay by the LHCb collaboration we present the meson dominance predictions for other weak decays of the B_c^+ into B_s^0 or B^0 in the form of branching ratios to the observed decay.
Electromagnetic interactions are introduced in the effective chiral Lagrangian for heavy mesons which includes light vector particles. A suitable notion of vector meson dominance is formulated. The constraints on the heavy meson -light vector and heavy meson-light pseudoscalar coupling constants are obtained using experimental $D^* \ra D \, γ$ branching ratios. These constraints are compared with values estimated from semi-leptonic transition amplitudes as well as from extension of the light meson coupling pattern. Application to the heavy baryon spectrum in the ``bound state " model is made.
The infinite tower of vector mesons encoded in holographic dual QCD bring drastic changes to the soliton structure of the nucleon. The nucleon is given by a point-like instanton in 5D surrounded by a vector meson cloud with the vector dominance restored by the infinite tower. I discuss the possible relevance of this structure in hot and dense hadronic matter.
We adopt the vector-meson-dominance approach to investigate Q^2-evolution of N-R transition form factors (N denotes nucleon and R an excited resonance) in the first and second resonance regions. The developed model is based upon conventional NRγ-interaction Lagrangians, introducing three form factors for spin-3/2 resonances and two form factors for spin-1/2 nucleon excitations. Lagrangian form factors are expressed as dispersionlike expansions with four or five poles corresponding to the lowest excitations of the mesons ρ(770) and ω(782). Correct high-Q^2 form factor behavior predicted by pert…
The decay $η'\rightarrowπ^0γγ$ is studied theoretically in the framework of the Vector Meson Dominance model (VMD). We find theoretically a significant contribution of the interference of $ω-ρ$ and provide theoretical Dalitz-plots. Comparison with the experimental results of BES-III \cite{BES-III} is done. We find some tension between our predicted value and the observed result. Our calculations can be also checked using the data of GAMS-$4π$.
A current-current correlator with the quantum numbers of the omega meson is studied in a nuclear medium. Using weighted finite energy sum rules and dispersion relations for the current-nucleon forward scattering amplitude it is shown that strict vector meson dominance and QCD sum rules are incompatible with each other. This implies that at least one of these concepts -- which are both very powerful in the vacuum -- has to fade in the nuclear environment.
The hypothesis is scrutinized that the weak interaction of hadronic systems at low energies is dominated by the coupling of the pseudoscalar, vector, and axial-vector mesons to the weak gauge bosons. The strength of the weak coupling of the rho(770) meson is uniquely determined by vector-meson dominance in electromagnetic interactions; flavor and chiral symmetry breaking effects modify the coupling of other vector mesons and axial-vector mesons. Many decay rates are calculated and compared to experimental data and partly to predictions of other models. A parameter-free description of the decay…
After describing the SU(2) linear sigma model (L$σ$M), we dynamically generate it using the B.W. Lee null tadpole sum (characterizing the true vacuum) together with the dimensional regularization lemma. Next we generate the chiral-limiting (CL) nonstrange and strange constituent quark masses ${\hat m}=325.7$ MeV; $m_s=486$ MeV away from the CL. Finally, we study vector meson dominance (VMD) and the pion, kaon charge radii and the loop-order $ρ\toπγ$, $π^0\toγγ$ amplitudes in the quark model. Lastly, we verify this procedure using tree-order VMD graphs.
We study scalar, pseudoscalar, vector, and axial-vector mesons with non-strange and strange quantum numbers in the framework of a linear sigma model with global chiral $U(N_f)_L \times U(N_f)_R$ symmetry. We perform a global fit of meson masses, decay widths, as well as decay amplitudes. The quality of the fit is, for a hadronic model that does not consider isospin-breaking effects, surprisingly good. We also investigate the question whether the scalar $\bar{q}q$ states lie below or above 1 GeV and find the scalar states above 1 GeV to be preferred as $\bar{q}q$ states. Additionally, we also d…
The Poincare invariant coupled-channel formalism for two-particle systems interacting via one-particle exchange, which has been developed and applied to vector mesons in Ref. [1] is applied to axial vector mesons. We thereby extend the previous study of a dynamical treatment of the Goldstone-boson exchange by comparison with the commonly used instantaneous approximation to the case of orbital angular momentum l=1. Effects in the mass shifts show more variations than for the vector-meson case. Results for the decay widths are sizable, but comparison with sparse experimental data is inconclusive…
We outline the extension of the globally chirally invariant Nf = 2 linear sigma model with vector and axial-vector degrees of freedom to Nf=3. We present preliminary results concerning the scalar meson masses.
In this work we shall investigate the mass modifications of scalar mesons $\left( D_{0}, B_{0}\right)$,vector mesons $\left( D^{\ast}, B^{\ast}\right)$ and axial-vector mesons $\left(D_{1}, B_{1}\right)$ at finite density and temperature of the nuclear medium. The above mesons are modified in the nuclear medium through themodification of quark and gluon condensates. We shall find the medium modification of quark and gluon condensates within chiral SU(3) model through the medium modification of scalar-isoscalar fields $σ$ and $ζ$ at finite density and temperature. These medium modified quark an…
Using the calculated values of the strong coupling constants of the heavy sextet spin-3/2 baryons to sextet and antitriplet heavy spin-1/2 baryons with light mesons within the light cone QCD sum rules method, and vector meson dominance assumption, the radiative decay widths are calculated. These widths are compared with the "direct" radiative decay widths predicted in the framework of the light cone QCD sum rules.
A renormalizable non-abelian vector meson dominance model coupled to pions is constructed which exhibits a ${\rm SO}\left(4,3\right)$ vacuum symmetry. Tree-level predictions for $p$-$p$ scattering lengths and slopes at leading order are in reasonable agreement with experiment.
Extended vector meson dominance model, that allows to describe the electromagnetic form factors of nucleons obeying the asymptotic quark counting rule prescriptions and contains the minimal number of free parameters, is presented. We get a reasonable fit of form factors over experimentally available space-like region of momentum transfer and get also reasonable results in the time-like region.
We prove that recent data demonstrates unequivocally that the scalar meson $f_0$(980) is mostly composed of $s\bar{s}$ quarks and that the coupling of $f_0$ to photons and mesons is in agreement with the linear sigma model.
We discuss and test the assumptions of the chirally normalized vector meson dominance model (CN-VMD), as it is used for tau decays. We compare the CN-VMD amplitudes with those using on-shell couplings, derived directly from experimental data. We discuss in detail the $3π$, $K K π$ and $2π$ final states. We suggest that the true values for the $K_1$ widths might be larger than those quoted in the Review of Particle Physics.
Low energy effective couplings of baryons' constituent quarks to light vector and axial mesons are derived by considering quark polarization for a dressed one gluon exchange quark interaction. The quark field is splitted into two components, one for background constituent quarks and another one for quark-antiquark states, light mesons and the scalar chiral condensate. By considering a large quark effective mass derivative expansion, several effective coupling constants are resolved as functions of the original model parameters and of components of the quark and gluon propagators. Besides the l…
Pade Approximants can be used to go beyond Vector Meson Dominance in a systematic approximation. We illustrate this fact with the case of the pion vector form factor and extract values for the first two coefficients of its Taylor expansion. Pade Approximants are shown to be a useful and simple tool for incorporating high-energy information, allowing an improved determination of these Taylor coefficients.
We study a vector dominance model which predicts a fairly large number of currently interesting decay amplitudes of the types S -> γγ, V -> S γand S -> V γ, where S and V denote scalar and vector mesons, in terms of three parameters. As an application, the model makes it easy to study in detail a recent proposal to boost the ratio Gamma(phi -> f_0 gamma) / Gamma(phi -> a_0 gamma) by including the isospin violating a_0 - f_0 mixing. However we find that this effect is actually small in our model.
Non-exotic scalar-meson resonances in S-wave meson-meson scattering are studied in the light of a unitarised Schroedinger model. The resulting poles in the scattering matrices, by analytical continuation into the complex-energy plane, are grouped into nonets of isoscalar, isodoublet, and isotriplet resonances. All singularities can be related to quark-antiquark confinement states, the light-quark nonet of which has ground states at 1.3 to 1.4 GeV and level spacings of some 300-400 MeV, except for a nonet of light scalar mesons below 1 GeV. All non-exotic S-wave resonances reported by experimen…
The axial anomaly is responsible for the masses and mixing of the mesons $η$ and $η'$. An open question is if (and to what extent) it affects also other hadrons. We show that anomalous terms can be important to understand the spectroscopy of the pseudotensor mesons $η_2 (1645)$ and $η_2 (1870)$. In fact, pseudotensor mesons belong to a so-called heterochiral multiplet, for which a quadratic mixing term between nonstrange and strange isoscalar members arises. On the contrary, for so-called homochiral multiplets, such as the ground-state (axial-)vector and tensor mesons, this mixing is not possi…
We study the light vector and axial-vector mesons. According to the hadrogenesis conjecture the nature of the two types of states is distinct. The axial-vector mesons are generated dynamically by coupled-channel interactions based on the chiral Lagrangian written down in terms of the Goldstone bosons and the light vector mesons. We propose a novel counting scheme that arises if the chiral Lagrangian is supplemented by constraints from large-N_c QCD in the context of the hadrogenesis conjecture. The counting scheme is successfully tested by a systematic study of the properties of vector mesons.…
The momentum-space bosonization method is extended to the case of a Nambu--Jona-Lasinio type model with vector and axial-vector mesons. The method presented gives the possibility of deriving any meson vertex function to all orders in momenta and to the leading order in $1/N_c$. Two-point functions, which describe one-particle transitions to the hadronic vacuum, and meson self-energies are considered. We find new relations which generalize the well-known KSFR relation and both the first and the second Weinberg sum rules. These result from a consistent treatment of higher order terms in the mome…
In this paper, we address the universality problem in the mass-mixing representation of vector meson dominance. First we stress the importance of using physical (mass eigenstate) fields in order to get the correct $q^2$ dependence of the pion form factor. Then we show that, when a direct coupling of the (proto-)photon to the pions is included, it is not necessary to invoke universality. Our method is similar to the delocalization idea in some deconstrunction theories.
We observed the impact of finite magnetic field on the in-medium mass and decay constant of isospin averaged vector $D^*(D^{*^+},D^{*^0})$ and axial-vector $D_1(D^+_1, D^0_1)$ mesons. The quark and gluon condensates of the nuclear medium at finite magnetic field, temperature, isospin asymmetry, and density have been obtained by the meson exchange scalar fields within the chiral SU(3) model. The medium attributes modify the scalar and vector density of nuclear medium and this variation reflects in the in-medium mass and decay constant of spin 1 $D$ mesons. We calculate these observables by comp…
Motivated by recent estimates of the isospin-violating process tau \to eta pi nu_tau, mostly relying on the rho and a_0 dominance of the relevant form factors near threshold, we present an assessment for the branching ratio that accounts for additional, potential, effects from the lowest radial excitations rho(1450) and a_0(1450), respectively, also lying in the decay phase space.
We study the electromagnetic pion form factor and the VV - AA two point function for momenta -(600 MeV)^2 < q^2 < (600 MeV)^2 and we note the similarity between vector meson dominance and two versions of the free constituent quark model. The similarity is more striking when the momentum dependence of the quark mass is taken into account. We consider the implications for QCD and other theories.
It is pointed out that the radiative decays of a $ϕ$ meson, $\phirho$ and $\phiom$, receive dominant contributions from the pseudoscalar ($P = η, η^{'}$) exchanges. Using the vector meson dominance model, we find that $B (\phirho) \approx 1.3 \times 10^{-4}$ and $B (\phiom) \approx 1.5 \times 10^{-5}$, which are mainly from the $η^{'}$ pole. Thus, these decays are well within the reach of the $ϕ$ factory. Our estimates are a few orders of magnitude larger than the chiral loop contributions in the heavy vector meson chiral lagrangian, which is about ( a few ) $\times 10^{-9}$.
A model is developed for electromagnetic form factors of the charged and neutral K-mesons. The formalism is based on ChPT Lagrangians with vector mesons. The form factors, calculated without fitting parameters, are in a good agreement with experiment for space-like and time-like photon momenta. Contribution of the two-kaon channels to the muon anomalous magnetic moment a_μis calculated.
By using a thermal Finite Energy QCD Sum Rule, we are able to establish the temperature dependence of the $g_{ωρπ}(T)$ strong coupling. It turns out that this coupling decreases as a function of temperature, vanishing at the critical temperature. This corresponds to a possible deconfining phenomenological signal. This result, together with the Vector Meson Dominance (VMD) expression for the amplitude $π^{0} \to γγ$, allows us to establish that this amplitude also vanishes at the critical temperature, in agreement with previous independent analysis. This results supports, once again, the validi…
We calculate the effects of finite density of isospin asymmetric strange hadronic matter, for different strangeness fractions, on the in-medium properties of vector $\left( D^{\ast}, D_{s}^{\ast}, B^{\ast}, B_{s}^{\ast}\right)$ and axial-vector $\left( D_{1}, D_{1s}, B_{1}, B_{1s}\right)$ mesons using chiral hadronic SU(3) model and QCD sum rules. We focus on the evaluation of in-medium mass-shift and shift of decay constant of above vector and axial vector mesons. In QCD sum rule approach the properties e.g. masses and decay constants of vector and axial vector mesons are written in terms of …
We summarize some features of the vector meson dominance model which was recently proposed for studying radiative decays involving the scalar mesons. Using the experimental values of $Γ(a_0 \to γγ)$, $Γ(f_0 \to γγ)$ and $Γ(ϕ\to a_0 γ)$ as inputs, we show that the model predicts a large hierarchy between $Γ(a_0 \to ωγ)$ and $Γ(a_0 \to ργ)$ as well as between $Γ(f_0 \to ωγ)$ and $Γ(f_0 \to ργ)$.
We explore the validity of vector meson dominance in the radiative decay of the $b_1(1235)$ meson. In order to explain the violation of the vector meson dominance hypothesis in this decay process, we investigate a model where the $b_1$ meson strongly couples with the local current in tensor bilinear representation. The tensor representation is investigated in the framework of the operator product expansion and we found a low energy decay process that does not follow the usual vector meson dominance hypothesis. The $ω$-like intermediate meson state of quantum numbers $I^G(J^{PC}) = 0^{-}(1^{--}…
Heavy and heavy-light tensor and axial-tensor mesons in the Covariant Spectator Theory
Centro de Ciências e Tecnologias Nucleares and Departamento de Engenharia e Ciências Nucleares, Instituto Superior Técnico, Universidade de Lisboa（里斯本大学技术研究所核科学与工程系及核科学与技术中心）；Departamento de Física, Universidade de Évora（埃武拉大学物理系）；Laboratório de Instrumentação e Física Experimental de Partículas—LIP（粒子实验物理与仪器实验室）
Historically vector-meson physics arose along two different paths to be reviewed in Sections 1 and 2. In Section 3, the phenomenological consequences will be discussed with an emphasis on those aspects of the subject matter relevant in present-day discussions on deep inelastic scattering in the diffraction region of low values of the Bjorken variable.
We study the decays of the lightest axial-vector and pseudovector mesons, interpreted as quark-antiquark states, into a vector and a pseudoscalar meson. We show that the quarkonium assignment delivers a good description of the decays and allows also to make further testable predictions. In the kaonic sector, the physical resonances $K_{1}(1270)$ and $K_{1}(1400)$ emerge as mixed objects of an axial vector state $K_{1,A}$ and a pseudovector state $K_{1,B}$. We determine the mixing angle as $\left\vert θ_{K}\right\vert=\left(33.6\pm4.3\right) ^{\circ}$, a value compatible with previous studies b…
As a first step towards a realistic phenomenological description of vector and axial-vector mesons in nuclear matter, we calculate the spectral functions of the $ρ$ and the $a_1$ meson in a chiral baryon-meson model as a low-energy effective realization of QCD, taking into account the effects of fluctuations from scalar mesons, nucleons, and vector mesons within the Functional Renormalization Group (FRG) approach. The phase diagram of the effective hadronic theory exhibits a nuclear liquid-gas phase transition as well as a chiral phase transition at a higher baryon-chemical potential. The in-m…
