Meson Effective Theory Research Articles

Complex-mass renormalization in chiral effective field theory

We consider a low-energy effective field theory of vector mesons and Goldstone bosons using the complex-mass renormalization. As an application we calculate the mass and the width of the ρ meson.

Electromagnetic form factors from the fifth dimension

We analyse various U(1)EM form factors of mesons at strong coupling in an = 2 flavored version of = 4 SYM which becomes conformal in the UV. The quark mass breaks the conformal symmetry in the IR and generates a mass gap. In the appropriate limit, the gravity dual is described in terms of probe D7-branes in AdS5 × S5. By studying the D7 fluctuations we find the suitable terms in a ``meson effective theory which allow us to compute the desired form factors, namely the γπρ and γf0ρ transition form factors. At large q2 we find perfect agreement with the naive parton model counting, which is a consequence of the conformal nature of our model in the UV. By using the same tools, we can compute the γ*γ*π form factor. However this channel is more subtle and comparisons to the QCD result are more involved.

Baryons in holographic QCD

We study baryons in holographic QCD with $\mathrm{D}4/\mathrm{D}8/\overline{\mathrm{D}8}$ multi-D-brane system. In holographic QCD, the baryon appears as a topologically nontrivial chiral soliton in a four-dimensional effective theory of mesons. We call this topological soliton brane-induced Skyrmion. Some review of $\mathrm{D}4/\mathrm{D}8/\overline{\mathrm{D}8}$ holographic QCD is presented from the viewpoints of recent hadron physics and QCD phenomenologies. A four-dimensional effective theory with pions and $\ensuremath{\rho}$ mesons is uniquely derived from the non-Abelian Dirac-Born-Infeld (DBI) action of D8 brane with D4 supergravity background at the leading order of large ${N}_{c}$, without small amplitude expansion of meson fields to discuss chiral solitons. For the hedgehog configuration of pion and $\ensuremath{\rho}$-meson fields, we derive the energy functional and the Euler-Lagrange equation of brane-induced Skyrmion from the meson effective action induced by holographic QCD. Performing the numerical calculation, we obtain the soliton solution and figure out the pion profile $F(r)$ and the $\ensuremath{\rho}$-meson profile $\stackrel{\texttildelow{}}{G}(r)$ of the brane-induced Skyrmion with its total energy, energy density distribution, and root-mean-square radius. These results are compared with the experimental quantities of baryons and also with the profiles of standard Skyrmion without $\ensuremath{\rho}$ mesons. We analyze interaction terms of pions and $\ensuremath{\rho}$ mesons in brane-induced Skyrmion, and find a significant $\ensuremath{\rho}$-meson component appearing in the core region of a baryon.

Brane-Induced Skyrmions

We study baryons in holographic QCD with D4/D8/\overline D8 multi D brane system. In holographic QCD, the baryon appears as a topologically non-trivial chiral soliton in a four-dimensional effective theory of mesons, which is called ‘Brane-induced Skyrmion’. We derive and calculate the Euler-Lagrange equation for the hedgehog configuration with chiral profile F(r) and ρ-meson profile \tildeG(r), and obtain the soliton solution of the holographic QCD.

RESUMMATION STUDY ON VECTOR MESON DECAYS AND CHIRAL SYMMETRY SPONTANEOUSLY BREAKING IN CHIRAL CONSTITUENT QUARK MODEL

We study on-shell decays of light vector meson resonances ρ, K* and ϕ in the framework of chiral constituent quark model using resummation calculations. Such studies are necessary for showing that dynamics described by chiral Lagrangian works well at this energy scale. The effective action is derived by a proper vertex method, where resummation of all orders of momentum expansion is accomplished. Also studied are the loop effects of pseudoscalar meson, which play an important role at this energy scale. The numerical results agree well with the experimental data. A new method to explore the chiral symmetry spontaneously breaking (CSSB) is proposed. It is found that the unitarity of the effective meson theory resulted from resummation derivations demands an upper-limit to the momentum of vector meson. This upper-limit, being critical point, is just the energy scale of CSSB, and is found to be flavor-dependent.

J/ψcouplings to charmed resonances and toπ

We present an evaluation of the strong couplings JD^(*)D^(*) and JD^(*)D^(*)pi by an effective field theory of quarks and mesons. These couplings are necessary to calculate pi+J/psi --> D^(*)+barD^(*) cross sections, an important background to the J/psi suppression signal in the quark-gluon plasma. We write down the general effective lagrangian and compute the relevant couplings in the soft pion limit and beyond.

Current quark mass and g−2 of muon and ee+→ π+π−

Based on a phenomenologically successful effective chiral theory of pseudoscalar, vector, and axial-vector mesons the dependences of ρ– ω mixing and the vertex ωππ on m d − m u are found. Using the new data of ee +→ π − π +, m d − m u has been determined to be 4.24 MeV. The form factor of pion agrees with data in both space- and time-like regions. The branching ratio of τ→ ππν is computed to be 25.14% which agrees with data. CVC is satisfied. The values of g−2 of muon from ππ channel are calculated in the range of q 2<1.3 2 GeV 2.

Low-energy limit of chiral meson theory

Based on a phenomenologically successful effective chiral theory of pseudoscalar, vector, and axial-vector mesons, all the coefficients of the chiral perturbation theory are predicted. There is no new adjustable parameter in these predictions. Up to O(m2q) the formulas of the masses of the pseudoscalar mesons are the same as the ones obtained by ChPT.

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.

Nonperturbative determination of heavy meson bound states

In this paper we obtain a heavy meson bound state equation from the heavy quark equation of motion in heavy quark effective theory (HQET) and the heavy meson effective field theory we developed very recently. The bound state equation is a covariant extention of the light-front bound state equation for heavy mesons derived from light-front QCD and HQET. We determine the covariant heavy meson wave function variationally by minimizing the binding energy �. Subsequently the other basic HQET parameters �1 and �2, and the heavy quark masses mb and mc can also be consistently determined.

Nonperturbative determination of heavy meson bound states

In this paper we obtain a heavy meson bound state equation from the heavy quark equation of motion in heavy quark effective theory (HQET) and the heavy meson effective field theory we developed very recently. The bound state equation is a covariant extention of the light-front bound state equation for heavy mesons derived from light-front QCD and HQET. We determine the covariant heavy meson wave function variationally by minimizing the binding energy $\bar{\Lambda}$. Subsequently the other basic HQET parameters $\lambda_1$ and $\lambda_2$, and the heavy quark masses $m_b$ and $m_c$ can also be consistently determined.

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

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.

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.

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.

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.

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.

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.

Scaling behavior in soliton models

In the framework of chiral soliton models we study the behavior of static nucleon properties under rescaling of the parameters describing the effective meson theory. In particular we investigate the question of whether the Brown-Rho scaling laws are general features of such models. When going beyond the simple Skyrme model we find that restrictive constraints need to be imposed on the mesonic parameters in order to maintain these scaling laws. Furthermore, in the case when vector mesons are included in the model it turns out that the isoscalar form factor no longer scales according to these laws. Finally we note that, in addition to the exact scaling laws of the model, one may construct approximate local scaling laws, which depend of the particular choice of Lagrangian parameters.