Lagrangian For Mesons Research Articles

π0, η, η' → γγ Decays and the Explicit Chiral Symmetry Breaking

Corrections to the Wess–Zumino–Witten anomaly caused by the explicit breaking of the SU(3) times SU(3) chiral symmetry are studied using the effective meson Lagrangian based on the Nambu–Jona-Lasinio model with the simultaneous expansion in derivatives, current quark masses, and 1/Nc powers. The leading contribution and the first correction for the amplitudes of the π0, η, η' → γγ decays and the contact term in the eta {text{/}}eta {kern 1pt} ' to {{pi }^{ + }}{{pi }^{ - }}gamma amplitudes have been calculated. The results are compared with similar 1/Nc chiral perturbation calculations and existing experimental data.

π0–η–η' Mixing in the Theory with Four-Quark Interactions

Mass formulas, mixing angles, and decay constants of the pseudoscalar π0, η, and η' mesons have been obtained in the theory with four-quark interactions with an accuracy to mathcal{O}(1{text{/}}N_{{text{c}}}^{2}) terms inclusively. Unlike the standard Nambu–Jona-Lasinio model, the meson Lagrangian has been obtained using the Volterra series, which allows a more detailed description of effects caused by the inequality of quark masses. The results have been compared to similar calculations in the 1/Nc chiral perturbation theory. The first corrections to the interaction violating the Zweig formulas have been calculated, and it has been shown that they are important for the description of the mass spectrum of the η–η' mesons.

Chiral effective Lagrangian for excited heavy-light mesons from QCD

We derive the chiral effective Lagrangian for excited heavy-light mesons from QCD under proper approximations. We focus on the chiral partners with and which amounts to (1+, 2+) and (1−, 2−) states respectively. The low energy constants including the masses of the chiral partners are calculated. The calculated spectrum for the excited mesons are found roughly consistent with experimental data. In addition, our results indicate that quantum numbers of B J (5970) can be identified with 1− or 2−.

QED corrections in overline{B}to overline{K}{mathrm{ell}}^{+}{mathrm{ell}}^{-} at the double-differential level

We present a detailed analysis of QED corrections to overline{B}to overline{K}{mathrm{ell}}^{+}{mathrm{ell}}^{-} decays at the double-differential level. Cancellations of soft and collinear divergences are demonstrated analytically using the phase space slicing method. Whereas soft divergences are found to cancel at the differential level, the cancellation of the hard-collinear logs ln mℓ require, besides photon-inclusiveness, a specific choice of kinematic variables. In particular, hard-collinear logs in the lepton-pair invariant mass distribution (q2), are sizeable and need to be treated with care when comparing with experiment. Virtual and real amplitudes are evaluated using an effective mesonic Lagrangian. Crucially, we show that going beyond this approximation does not introduce any further infrared sensitive terms. All analytic computations are performed for generic charges and are therefore adaptable to semileptonic decays such as overline{B}to Dmathrm{ell}overline{nu } .

Chiral effective Lagrangian for heavy-light mesons from QCD

We derive the chiral effective Lagrangian for heavy-light mesons in the heavy quark limit from QCD under proper approximations. The low energy constants in the effective Lagrangian are expressed in terms of the light quark self-energy. With typical forms of the running coupling constant of QCD and the quark self-energy obtained from Dyson-Schwinger equations as well as lattice QCD, we estimate the low energy constants in the model and the strong decay widths. A comparison with data and some discussions of the numerical results are presented.

Inelastic meson-meson scattering in hadronic matter

We review studies of inelastic meson-meson scattering. In nonperturbative schemes with chiral-perturbation-theory Lagrangians and in models based on effective meson Lagrangians, inelastic meson-meson scattering leads to the successful identification of resonances in meson-meson reactions, adequate inclusion of final state interactions in particle decays, and so on. For mesons of which each consists of a quark and an antiquark, inelastic meson-meson scattering may be caused by quark-antiquark annihilation, quark-antiquark creation, quark interchange, and quark-antiquark annihilation and creation. In transition amplitudes for meson-meson scattering mesonic quark-antiquark relative-motion wave functions depend on hadronic matter, and transition potentials are given in perturbative quantum chromodynamics. Via transition amplitudes the cross sections for inelastic meson-meson scattering depend on the temperature of hadronic matter. Some prominent temperature dependence of the cross sections has been found. Inelastic meson-meson scattering becomes even more significant in proton-proton collisions and lead-lead collisions at the Large Hadron Collider.

Chiral Imbalance in Hadron Matter: Its Manifestation in Photon Polarization Asymmetries

The possibility of the formation of a local parity breaking (LPB) in a quark-hadron medium is examined as a result of chiral symmetry violation, i.e, the appearance of difference between the average densities of right- and left-handed quarks in the fireball after heavy-ion collisions (HIC). Using the effective meson Lagrangian motivated by QCD extended to the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise due to mixing of $\pi$ and $a_0$ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We conjecture that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, FAIR and NICA accelerators.

Chiral Lagrangians for mesons with a single heavy quark

We construct the relativistic chiral Lagrangians for heavy-light mesons $(Q\bar{q})$ to the $\mathcal{O}(p^4)$ order. From $\mathcal{O}(p^2)$ to $\mathcal{O}(p^4)$, there are 17, 67, and 404 independent terms in the flavor $SU(2)$ case and 20, 84, and 655 independent terms in the flavor $SU(3)$ case. The Lagrangians in the heavy quark limit are also obtained. From $\mathcal{O}(p^2)$ to $\mathcal{O}(p^4)$, there are 7, 25, and 136 independent terms in the flavor $SU(2)$ case and 8, 33, and 212 independent terms in the flavor $SU(3)$ case. The relations between low-energy constants based on the heavy quark symmetry are also given up to the $\mathcal{O}(p^3)$ order.

On pion and kaon decay constants and their chiral SU(3) extrapolations

We consider the dependence of the pion and kaon decay constants on the up, down and strange quark masses in QCD with strict isospin symmetry. The role of dynamical vector meson degrees of freedom is scrutinized in terms of an effective chiral Lagrangian for vector mesons. Applying a set of low-energy parameters as determined previously from QCD lattice data on the masses of the light vector mesons from PACS-CS, QCDSF-UKQCD and HSC we compute its implications on the pion and kaon decay constants for QCD lattice ensembles of HPQCD, CLS and ETMC. It is shown that with Gasser-Leutwyler L4 and L5 parameters fixed to the empirical decay constants an accurate reproduction of their values at unphysical quark masses as computed by HPQCD, CLS and ETMC is achieved. Results for the masses of the light vector meson, the ω−ϕ mixing angles and the quark mass ratios for the ensembles used by HPQCD, CLS and ETMC are discussed.

Hadronic electroweak current and π−a1 mixing

It is found that in the presence of electroweak interactions the gauge covariant diagonalization of the axial-vector--pseudoscalar mixing in the effective meson Lagrangian leads to a deviation from the vector meson and the axial-vector meson dominance of the entire hadronic electroweak current. The essential features of such a modification of the theory are investigated in the framework of the extended Nambu-Jona-Lasinio model with explicit breaking of chiral $U(2)\ifmmode\times\else\texttimes\fi{}U(2)$ symmetry. The Schwinger-DeWitt method is used as a major tool in our study of the real part of the relevant effective action. Some straightforward applications are considered.

Electromagnetic interactions of mesons induced by axial-vector–pseudoscalar mixing

It is shown that the diagonalization of the axial-vector -- pseudoscalar transitions in the effective meson Lagrangian in presence of electromagnetic interactions leads to a deviation from the vector meson dominance picture which usually arises in the Nambu - Jona-Lasinio model. The essential features of such modification of the theory are studied. Some important examples are considered in detail.

Electromagnetic Interactions of Mesons and the πa1 Diagonalization

It has been demonstrated that, contrary to the commonly accepted viewpoint, electromagnetic interactions cannot be consistently included in the Nambu–Jona-Lasinio model within vector meson dominance. This refers to the procedure for removing the πa1 transition in the effective meson Lagrangian. By the example of the a1(1260)→γπ+π- radiative decay, it has been demonstrated that the gauge invariance condition for the amplitude gives rise to an electromagnetic vertex describing the direct emission of a photon and a pion by a quark–antiquark pair. Surface terms appearing in the calculation of an anomalous triangular quark diagram, where one of the vertices is the interaction violating the vector-dominance hypothesis, play a key role in satisfying the Ward identities.

QCD with Chiral Chemical Vector: Models Versus Lattices

A formation of Local Parity Breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. LPB in the fireball can be produced by a difference between the number densities of right- and left-handed chiral fermions (Chiral Imbalance) which is implemented by a chiral (axial) chemical potential. Based on the effective meson Lagrangian motivated by QCD in the chiral medium the properties of light scalar and pseudoscalar mesons (π, a0) are analyzed. It is found that exotic decays of scalar mesons arise as a result of mixing of π and a0 vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We believe that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.

Nucleons in Nuclear Matter and Properties of Nuclei

In this contribution we discuss the properties of nucleons and atomic nuclei in the framework of in-medium modified chiral soliton model. The mesonic Lagrangian of the model takes into account an influence of surrounding nuclear environment to the nucleon properties. The model correctly describes the Equations of State of isospin-symmetric and isospin-asymmetric nuclear matter near the nuclear saturation density ρ0. An extrapolation of the results to high density region allows to describe the properties of neutron stars. The model also can be applied to analysis of the properties of mirror nuclei.

Exotic meson decays and polarization asymmetry in hadron environment with chiral imbalance

The possibility of the formation of a local parity breaking in a quark-hadron medium is described as a result of a violation of chiral symmetry, i.e, the difference between the average numbers of right and left -handing quarks in the fireball after HIC.The phenomenology of LPB in the fireball induces the introduction of a topological charge and, accordingly, a topological (chiral) chemical potential. Using the effective meson Lagrangian motivated by QCD in the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise as a result of mixing of π and a0 vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We consider that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.

A general framework to diagonalize vector–scalar and axial-vector–pseudoscalar transitions in the effective meson Lagrangian

A new mathematical framework for the diagonalization of the nondiagonal vector–scalar and axial-vector–pseudoscalar mixing in the effective meson Lagrangian is described. This procedure has unexpected connections with the Hadamard product of n×n matrices describing the couplings, masses, and fields involved. The approach is argued to be much more efficient as compared with the standard methods employed in the literature. The difference is especially noticeable if the chiral and flavor symmetry is broken explicitly. The paper ends with an illustrative application to the chiral model with broken U(3)L×U(3)R symmetry.

Chiral transformations of spin-1 mesons in the non-symmetric vacuum

A new sort of chiral transformations for spin-1 states is obtained as a result of a linearized diagonalization of πa1 mixing in the effective meson Lagrangian. Using this symmetry argument, we argue that there is no physical distinction between such theory and the theory in which a covariant nonlinear diagonalization is used instead. As an illuminating example, the Nambu–Jona-Lasinio type model with the broken SU(2)×SU(2) chiral symmetry in the one-quark-loop approximation is considered.

Derivation of the effective chiral Lagrangian for pseudoscalar, scalar, vector, and axial-vector mesons from QCD

A previous formal derivation of the effective chiral Lagrangian for low-lying pseudoscalar mesons from first-principles QCD without approximations [Wang et al., Phys. Rev. D61, (2000) 54011] is generalized to further include scalar, vector, and axial-vector mesons. In the large Nc limit and with an Abelian approximation, we show that the properties of the newly added mesons in our formalism are determined by the corresponding underlying fundamental homogeneous Bethe--Salpeter equation in the ladder approximation, which yields the equations of motion for the scalar, vector, and axial-vector meson fields at the level of an effective chiral Lagrangian. The masses appearing in the equations of motion of the meson fields are those determined by the corresponding Bethe--Salpeter equation.

Axial-vector mesons and the problem of πa 1 mixing

In the framework of the Nambu–Jona-Lasinio (NJL) model, a mechanism for eliminating the off-diagonal πa 1 transitions from the effective meson Lagrangian is investigated. The problem is considered in the oneloop approximation for the quark loops. We employ the minimal superposition linear in the fields, a μ ' = a μ − c∂μπ, and show that the covariant transformation properties of both the axial-vector and vector physical fields are affected by this substitution. Contrary to some claims found in the literature, we demonstrate that the discussed change in covariant transformation properties of these fields does not result in various violations of chiral symmetry, but rather reduces to a redefinition of the S-matrix elements beyond the mass shell. At the same time, the covariant and noncovariant approaches yield identical on-shell results.

Exotic meson decays in the environment with chiral imbalance

An emergence of Local Parity Breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. LPB in the fireball can be produced by a difference between the number densities of right- and left-handed chiral fermions (Chiral Imbalance) which is implemented by a chiral (axial) chemical potential. The effective meson lagrangian induced by QCD is extended to the medium with Chiral Imbalance and the properties of light scalar and pseudoscalar mesons ($\pi, a_0$) are analyzed. It is shown that exotic decays of scalar mesons arise as a result of mixing of $ \pi $ and $ a_0 $ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains an unusual parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We hope that the above pointed indications of LPB can be identified in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.