Meson Theory Research Articles

Radiative decay of vector mesons

In this paper, radiative decays $\rho^0 \to \pi^+\pi^-\gamma, \pi^0\pi^0\gamma$ ,$\phi \to K^+K^-\gamma, K^0 \bar{K^0}\gamma$ are studied systematically in the U(3)$_L\timesU(3)_R$ chiral theory of mesons. The theoretical differential spectrum with respect to photon energy and branch ratio for $\rho^0 \to \pi^+\pi^-\gamma$ agree well with the experimental data. Differential spectrums and branch ratios for $\rho^0 \to \pi^0\pi^0\gamma, \phi \to K^+ K^-\gamma,\phi \to K^0\bar{K^0}\gamma$ are predicted. The process $\phi \to K^0 \bar{K^0} \gamma$ is relevant to precision measurment of CP-violation parameters in the kaon systerm at a $\phi$-factory. We give a complete estimate of the branch ratio for this decay process by including scalar resonance $f_0, a_0$ poles, nonresonant smooth amplitude and an abnormal parity process with $K^*$ pole which hasn't been considered before. We conclude that processes with intermediate $K^*$ do not pose a potential background problem for $\phi\to K^0\bar{K}^0$ CP violation experiments.

Dilepton spectra from decays of light unflavored mesons

The invariant mass spectrum of the $e^{+}e^{-}$ and $\mu ^{+}\mu ^{-}$ pairs from decays of light unflavored mesons with masses below the $\phi (1020)$-meson mass to final states containing along with a dilepton pair one photon, one meson, and two mesons are calculated within the framework of the effective meson theory. The results can be used for simulations of the dilepton spectra in heavy-ion collisions and for experimental searches of dilepton meson decays.

Flavour-symmetry correction to the “naı̈ve” Zweig rule for the scalar-meson flavour singlet

We present flavour-symmetric couplings for the OZI-allowed three-meson vertices of effective meson theories, which, for the case of the two-meson channels to which the flavour-singlet scalar meson couples, are endowed with a correction factor with respect to the standard formula.

Axial-vector symmetry breaking and τ mesonic decays

Effective chiral theory of mesons beyond ChPT has been applied to study τ → 4πν,η3 piν. Theoretical results agree with data. A new axial-vector symmetry breaking is revealed from this theory. The mass gap between ϱ and a 1 mesons originates in this symmetry breaking. W and Z bosons gain mass from this symmetry breaking. m W = 1 2 gm t, mz = ρm W cosθ W with ρ ∼ 1, and G F = 1 2 2 m t 2

Electromagnetic Masses Anomaly of K*(892) in the Massive Yang–Mills Theory**The project supported in part by National Natural Science Foundation of China through C. N. YANG

Electromagnetic mass difference between neutral K* and charged K* has been calculated in the U(3)L × U(3)R chiral field theory of mesons. It has been revealed that the non-Abelian gauge structure of the massive Yang–Mills Lagrangian obeyed by K* plus VMD (vector meson dominance) causes the EM-mass of neutral one larger than charged one. Experiment supports this anomaly effect.

πKscattering in the effective chiral theory of mesons

In the framework of an effective chiral theory of mesons, pi K scattering is stydied. The scattering lengths, phase shifts, and cross sections are calculated. Theoretical results agree well with data. There is no new parameter in this study.

Quenched and partially quenched chiral perturbation theory for vector and tensor mesons

Quenched and partially quenched chiral perturbation theory for vector mesons is developed and is used to extract the chiral loop correction to the ϱ meson mass. Connections to fully quenched and totally unquenched chiral perturbation theory results are discussed. It is also shown that (partially) quenched perturbation theory for tensor mesons can be formulated analogously, and the chiral corrections for tensor meson masses are directly proportional to their counterparts in the vector meson sector. Utilizing this observation and non-relativistic quark model, we point out that the mass difference (m a 2 − 3 2 m ϱ) is “quenching-insensitive” in the large- N c limit. This quantity may be used for normalization of mass scale in lattice QCD calculations.

Effective field theory of heavy mesons

In this paper we present a detailed formulation for a recently proposed effective field theory to describe the nonperturbative QCD dynamics of heavy mesons. This effective theory incorporates with heavy quark symmetry (HQS) and the heavy quark effective theory (HQET). Heavy mesons in this theory are constructed as composite particles of a heavy quark bounded with the light degrees of freedom. The heavy meson properties in the heavy quark limit and the $1/m_Q$ corrections can then be explicitly evaluated from this effective theory. All the basic parameters of the HQET, namely, the heavy quark mass $m_Q$, the heavy meson residual mass $\overline{\Lambda}$, and the HQS breaking mass parameters $\lambda_1$ and $\lambda_2$, are consistently determined. $\lambda_1$ is found to be small due to a large cancellation between the heavy quark kinetic energy and the chromo-electric interaction between the heavy quark and light degrees of freedom. We also evaluate the Isgur-Wise function, the decay constant, and the axial-vector coupling constant of heavy mesons.

Chiral perturbation theory and chiral theory of mesons

We examine low energy limit of chiral theory of mesons through integrating out fields of vector and axial-vector mesons. The effective Lagrangian for pseudoscalar mesons at O has been obtained, and five low-energy coupling constants have been revealed. They are in good agreement with the results of 's at .

Chiral perturbation theory for tensor mesons

Interactions of $a_2, K^*_2, f_2$ and $f_2'$ tensor-mesons with low-energy $\pi, K, \eta, \eta'$ pseudo-scalar mesons are constrained by chiral symmetry. We derive a chiral Lagrangian of tensor mesons in which the tensor mesons are treated as heavy non-relativistic matter fields. Using $1/N_c$ counting, we derive relations among unknown couplings of the chiral Lagrangian. Chiral perturbation theory is applied to the tensor-meson mass matrix. At one-loop there are large corrections to the individual tensor meson masses, but the singlet-octet mixing angle remains almost unchanged. We argue that all heavy mesons of spin $\ge 1$ share common feature of chiral dynamics.

Matching the heavy vector meson theory

We show how to obtain a ``heavy'' meson effective lagrangian for the case where the number of heavy particles is not conserved. We apply the method in a simple example at tree level and perform then the reduction for the case of vector mesons in Chiral Perturbation Theory in a manifestly chiral invariant fashion. Some examples showing that ``heavy'' meson effective theory also works at the one-loop level are included.

ρ0-ω mixing in U(3)L×U(3)R chiral theory of mesons}

In this paper, U(3)$_L\times$ U(3)$_R$ chiral theory of mesons is extended to the leading order in quark mass expansion in order to evaluate the $\rho^0-\omega$ mixing. It is shown that the use of path integral method to integrate out the quark fields naturally leads to the $\rho^0-\omega$ mixing vertices, and this mixing is entirely from the quark loop in this theory. The off-shell behaviour of the mixing amplitude is analyzed. The on-shell mixing amplitude is obtained from the decay $\omega\to \pi^+\pi^-$. Furthermore, the constraints on the light quark mass parameters are extracted from the $\rho^0-\omega$ mixing and the mesons masses, and the mass splitting of $K^*(892)$-mesons is predicted.

Hypernuclei and baryon-baryon interaction

A central ΛN potential containing spin and charge dependences is constructed on the basis of an analysis of fundamental hypernuclear data (Λp scattering, the binding energies of the ground and excited states of hypernuclei). The lightest hypernuclei ( Λ 3 H, Λ 4 H, Λ 4 He) are calculated as a system of three or four particles on the basis of the highly efficient variational method. Heavier hypernuclei are considered in terms of a twobody model (Λ + undeformed nucleon core) corrected by comparison with direct 3–5-particle calculations. By comparing the results of the calculations of single and double Λ hypernuclei and taking the considerations of meson theory into account, it is possible to estimate the binding energies of charmed and other (b- and t-quark) supernuclei.

Generalization of the bound state model

In the bound state approach the heavy baryons are constructed by binding, with any orbital angular momentum, the heavy meson multiplet to the nucleon considered as a soliton in an effective meson theory. We point out that this picture misses an entire family of states, labeled by a different angular momentum quantum number, which are expected to exist according to the geometry of the three-body constituent quark model (for ${N}_{C}=3)$. To solve this problem we propose that the bound state model be generalized to include orbitally excited heavy mesons bound to the nucleon. In this approach the missing angular momentum is ``locked up'' in the excited heavy mesons. In the simplest dynamical realization of the picture we give conditions on a set of coupling constants for the binding of the missing heavy baryons of arbitrary spin. The simplifications made include working in the large $M$ limit, neglecting nucleon recoil corrections, neglecting mass differences among different heavy spin multiplets, and also neglecting the effects of light vector mesons.

Unified effective theory for light mesons and heavy mesons

We present a unified effective field theory for the light mesons and heavy mesons which integrates many features from the quark model, vector dominance, chiral dynamics, Skyrmion physics, and the heavy quark effective theory into a single universal theory. By identifying the meson fields as the Bargmann-Wigner superfields with the direct product representation of a quark and antiquark and using the Bargmann-Wigner equation and Lagrangian, we can readily match the meson Lagrangian with the quark Lagrangian. Thus we not only incorporate various aspects of the quark contents into the meson fields but we can also transcribe the implementation of the chiral symmetry and spontaneous symmetry breakings from the quark Lagrangian to the meson Lagrangian. The physical light meson fields can be constructed nonlinearly from the quark and antiquark direct product representation, with the ${0}^{\ensuremath{-}}$ pseudoscalar mesons as the Goldstone mesons and the ${1}^{\ensuremath{-}}$ vector mesons as the non-Abelian gauge fields of the hidden local SU(3) symmetry. Phenomenological consequences and theoretical implications of this theory will be discussed. Various aspects of the heavy quark effective theory are automatically integrated into this formulation.

Meson-Nucleon Vertex Corrections in the Cutoff Field Theory and Tensor Coupling

At zero-density, meson-nucleon vertex corrections to vacuum polarization are studied in the $\sigma-\omega$ model with the cutoff. It is shown that the properties of the vertex corrections to vacuum polarization are somewhat different from those described by the ordinary renormalization procedures when the cutoff is small (< 5 GeV). The low-energy effective Lagrangian is constructed in the framework of the renormalization group method. The weak tensor and derivative couplings of meson-nucleon interactions may be needed in the low-energy effective theory of mesons and nucleons.

Quenched chiral perturbation theory for vector mesons

We develop quenched chiral perturbation theory for vector mesons made of light quarks, in the limit where the vector meson masses are much larger than the pion mass. We use this theory to extract the leading nonanalytic dependence of the vector meson masses on the masses of the light quarks. By comparing with analogous quantities computed in ordinary chiral perturbation theory, we estimate the size of quenching effects, observing that in general they can be quite large. This estimate is relevant to lattice simulations, where the $\rho$ mass is often used to set the lattice spacing.

The dipole polarisability of Zn $^{+}$ and the high- $\ell$ Rydberg levels of Zn

Quantum field theory in nonstationary curved Friedmann spacetime leads to the phenomenon of massive particles creation. The hypothesis that, at the end of inflation, gravitation creates from vacuum superheavy particles as some primordial matter decaying into quarks and leptons, leading to the observed baryonic charge, is investigated. Taking a complex scalar field for these particles, by analogy with K 0 meson theory, one obtains two components, the long-and short-lived ones, so that the long-lived component, after breaking the Grand Unification symmetry, has a long lifetime and is observed today as dark matter. The hypothesis, that ultra-high energy cosmic rays occur as a manifestation of superheavy dark matter, is considered, and some experimental possibilities of the proposed scheme are analyzed. Some new results on nonconformal scalar particle creation are presented.

Theory ofτmesonic decays

Studies of $\ensuremath{\tau}$ mesonic decays are presented. A mechanism for the axial-vector current at low energies is proposed. The VMD is used to treat the vector current. All the meson vertices of both normal parity and abnormal parity (Wess-Zumino-Witten anomaly) are obtained from an effective chiral theory of mesons. ${a}_{1}$ dominance is found in the decay modes of the $\ensuremath{\tau}$ lepton: $3\ensuremath{\pi}$, $f(1285)\ensuremath{\pi}$. Both the $\ensuremath{\rho}$ and the ${a}_{1}$ meson contribute to the decay $\ensuremath{\tau}\ensuremath{\rightarrow}{K}^{*}K\ensuremath{\nu}$; it is found that the vector current is dominant. CVC is tested by studying ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$. The branching ratios of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\omega}\ensuremath{\pi}\ensuremath{\nu}$ and $K\mathrm{K\ifmmode\bar\else\textasciimacron\fi{}}\ensuremath{\nu}$ are calculated. In terms of a similar mechanism the $\ensuremath{\Delta}s=1$ decay modes of the $\ensuremath{\tau}$ lepton are studied and ${K}_{a}$ dominance is found in $\ensuremath{\tau}\ensuremath{\rightarrow}{K}^{*}\ensuremath{\pi}\ensuremath{\nu}$ and ${K}^{*}\ensuremath{\eta}\ensuremath{\nu}$. The suppression of $\ensuremath{\tau}\ensuremath{\rightarrow}K\ensuremath{\rho}\ensuremath{\nu}$ is revealed. The branching ratio of $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\eta}K\ensuremath{\nu}$ is computed. As a test of this theory, the form factors of $\ensuremath{\pi}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\nu}$ and $K\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\nu}$ are determined. The theoretical results agree with data reasonably well.

Octet and decuplet magnetic and axial couplings from one-loop self-consistent perturbation theory

Octet and decuplet wave functions, obtained in a recent precision fit to the spectrum using one-loop self-consistent perturbation theory of mesons and gluons interacting with bagged relativistic quarks, are used to evaluate axial couplings and magnetic moments. Results are fully competitive with other models and provide further support to one-loop self-consistent perturbation theory as a useful model of baryon structure.