arXiv subjects

M. Nagy

Publications and source records attributed to M. Nagy.

34 records · Page 2Linked to original sources

arXiv2003

On the nature of $f_0$ mesons below 1.9 GeV and lower scalar nonets

The combined 3-channel analysis of experimental data on the coupled processes $ππ\toππ,K\bar{K},ηη$ is carried out in the channel with the vacuum quantum numbers. An approach, using only first principles (analyticity and unitarity) and the uniformizing variable, is applied. Definite indications of the QCD nature of the $f_0$ resonances below 1.9 GeV are obtained, among them a surprising indication for $f_0(980)$ to be the $ηη$ bound state. An assignment of the scalar mesons below 1.9 GeV to lower nonets is proposed.

hep-ph↗

arXiv2003

Mesons of the $f_0$-family in the processes $ππ\toππ,K\bar{K},ηη$ up to 1.9 GeV

In combined 2- and 3-channel analyses of experimental data on the coupled processes $ππ\toππ,K\bar{K},ηη$ in the channel with $I^GJ^{PC}=0^+0^{++}$, various scenarios of these reactions(with different numbers of resonances) are considered. In a model-independent approach, confirmation of the $σ$-meson below 1 GeV and definite indications of the QCD nature of other $f_0$ resonances are obtained. The conclusion on the linear realization of chiral symmetry is drawn.

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arXiv2002

Mesons of the $f_0$ family in processes $ππ\toππ,K\bar{K}$ up to 2 GeV and chiral symmetry

In a combined analysis of the experimental data on the coupled processes $ππ\toππ,K\bar{K}$ in the channel with $I^GJ^{PC}=0^+0^{++}$, the various scenarios of these reactions (with different numbers of resonances) are considered. In a model-independent approach, based only on analyticity and unitarity, a resonance is represented by of a pole cluster (poles on the Riemann surface) of the definite type that is defined by the state nature. The best scenario contains the resonances $f_0(665)$ (with properties of the $σ$-meson), ${f_0}(980)$ (with a dominant $s{\bar s}$ component), $f_0(1500)$ (with a dominant flavour-singlet, {\it e.g.}, glueball component) and the ${f_0}(1710)$ (with a considerable $s{\bar s}$ component). If the ${f_0}(1370)$ exists, it has a dominant $s{\bar s}$ component. The coupling constants of observed states with the considered channels and the $ππ$ and $K\bar{K}$ scattering lengths are obtained. The conclusion on the linear realization of chiral symmetry is drawn.

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arXiv2002

The $f_0$ Mesons in Processes $ππ\toππ, K\bar{K}$ and Chiral Symmetry

In a combined analysis of the experimental data on the coupled processes $ππ\toππ,K\bar{K}$ in the channel with $I^GJ^{PC}=0^+0^{++}$, the following results are obtained in a model-independent way: 1) The $f_0(665)$ state with properties of the $σ$-meson is proved to exist; 2) it is shown that the ${f_0}(980)$ and especially ${f_0}(1370)$ (if exists) have a dominant $s{\bar s}$ component; 3) indications of the glueball nature of the $f_0(1500)$ and of a considerable $s{\bar s}$ component in the ${f_0}(1710)$ are obtained; 4) conclusion on the linear realization of chiral symmetry is drawn.

hep-ph↗

arXiv2001

Model-independent approach as a tool of studying chiral symmetry

A simultaneous analysis (in the model-independent approach) of the $ππ$ scattering (from the threshold to 1.9 GeV) and of the $ππ\to K\overline{K}$ process (from the threshold to $\sim$ 1.46 GeV) is carried out in channel with $I^GJ^{PC}=0^+0^{++}$. The existence of the $f_0(665)$ state with properies of the $σ$-meson is proved. An indication for the glueball nature of the $f_0(1500)$ is obtained. A minimum scenario of the simultaneous description of the processes $ππ\toππ,K\overline{K}$ does without the ${f_0}(1370)$ resonance. A version including this state is also considered. In this case the ${f_0}(1370)$ resonance has the dominant $s{\bar s}$ component (the ratio of its coupling constant with the $ππ$ channel to the one with the $K\overline{K}$ channel is 0.12). The coupling constants of the observed states with the $ππ$ and $K\overline{K}$ systems and the $ππ$ and $K\overline{K}$ scattering lengths are obtained. A parameterless description of the $ππ$ background is given by allowance for the left-hand branch-point in the uniformizing variable. On the basis of this and of the fact that all the adjusted parameters for the $ππ$ scattering are only the positions of poles describing resonances, it is concluded that our model-independent approach is a valuable tool for studying the realization schemes of chiral symmetry. The existence of the $f_0(665)$ state and the obtained $ππ$-scattering length ($a_0^0\approx 0.27 m_{π^+}^{-1}$) seem to suggest the linear realization of chiral symmetry.

hep-ph↗

arXiv2001

Existence and Properties of the $f_0(665)$ State and Chiral Symmetry

On the basis of a simultaneous description of the isoscalar s-wave of $ππ$ scattering (from the threshold up to 1.9 GeV) and of $ππ\to K\bar{K}$ process (from the threshold to $\sim$ 1.4 GeV) in the model-independent approach, it is shown that there exists the $f_0(665)$ state with properies of the $σ$-meson, the glueball nature of $f_0(1500)$ is indicated, and the $f_0(1370)$ is assigned mainly to $s{\bar s}$ state. The coupling constants of the observed states with $ππ$ and $K\bar{K}$ systems and scattering lengths $a_0^0(ππ)$ and $a_0^0(K\bar{K})$ are calculated. The existence of the $f_0(665)$ state and the obtained $ππ$-scattering length ($a_0^0\approx 0.27 m_{π^+}^{-1}$) seem to suggest the linear realization of chiral symmetry.

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arXiv2000

Model-Independent Confirmation of the $σ$-Meson below 1 GeV and Indication for the $f_0(1500)$ Glueball

In the model-independent approach consisting in the immediate application to the analysis of experimental data of such general principles as analyticity and unitarity, a confirmation of the $σ$-meson at $\sim$ 665 MeV and an indication for the glueball nature of the $f_0(1500)$ state are obtained on the basis of a simultaneous description of the isoscalar s-wave channel of the $ππ$ scattering (from the threshold up to 1.9 GeV) and of the $ππ\to K\bar{K}$ process (from the threshold to $\sim$ 1.4 GeV where the 2-channel unitarity is valid). A parameterless description of the $ππ$ background is first given by allowance for the left-hand branch-point in the proper uniformizing variable. It is shown that the large $ππ$-background, usually obtained, combines, in reality, the influence of the left-hand branch-point and the contribution of a very wide resonance at $\sim$ 665 MeV. The coupling constants of the observed states with the $ππ$ and $K\bar{K}$ systems and lengths of the $ππ$ and $K\bar{K}$ scattering are obtained.

hep-ph↗

arXiv2000

Existence of the $σ$-meson below 1 GeV and $f_0(1500)$ glueball

On the basis of a simultaneous description of the isoscalar s-wave channel of the $ππ$ scattering (from the threshold up to 1.9 GeV) and of the $ππ\to K\bar{K}$ process (from the threshold to $\sim$ 1.4 GeV) in the model-independent approach, a confirmation of the $σ$-meson at $\sim$ 665 MeV and an indication for the glueball nature of the $f_0(1500)$ state are obtained. It is shown that the large $ππ$-background, usually obtained, combines, in reality, the influence of the left-hand branch-point and the contribution of a very wide resonance at $\sim$ 665 MeV. The coupling constants of the observed states with the $ππ$ and $K\bar{K}$ systems and lengths of the $ππ$ and $K\bar{K}$ scattering are obtained.

hep-ph↗

arXiv2000

Scalar Mesons in a Chiral Quark Model with Glueball

Ground-state scalar isoscalar mesons and a scalar glueball are described in a U(3)xU(3) chiral quark model of the Nambu--Jona-Lasinio (NJL) type with 't Hooft interaction. The latter interaction produces singlet-octet mixing in the scalar and pseudoscalar sectors. The glueball is introduced into the effective meson Lagrangian as a dilaton on the base of scale invariance. The mixing of the glueball with scalar isoscalar quarkonia and amplitudes of their decays into two pseudoscalar mesons are shown to be proportional to current quark masses, vanishing in the chiral limit. Mass spectra of the scalar mesons and the glueball and their main modes of strong decay are described.

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arXiv2000

Confirmation of the $σ$-Meson below 1 GeV and Indication for the $f_0(1500)$ Glueball

hep-ph↗

arXiv2000

Scalar Mesons and Glueballs in a Chiral U(3)xU(3) Quark Model with 't Hooft Interaction

In a U(3)x U(3) quark chiral model of the Nambu-Jona-Lasinio type with the 't Hooft interaction, the ground scalar isoscalar mesons and a scalar glueball are described. The glueball (dilaton) is introduced into the effective meson Lagrangian written in a chirally symmetric form on the base of scale invariance. The singlet-octet mixing of scalar isoscalar mesons and their mixing with the glueball are taken into account. Mass spectra of the scalar mesons and glueball and their strong decays are described.

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arXiv1998

Nucleon structure from the quasithreshold inverse pion electroproduction

The process $πN\to e^+e^- N$ (IPE), being a natural and unique laboratory for studying the hadron electromagnetic structure in the sub-$N\bar{N}$-threshold time-like region of the virtual-photon ``mass'' $λ^2$, turns out to be also very useful for investigating the nucleon weak structure. A theoretical basis of the methods for extracting practically model-independent values of the electromagnetic hadron form factors in the time-like region and for determining the weak structure of the nucleon in the space-like region from experimental data on IPE at low energies is outlined. The results of extracting, by those methods, the electromagnetic $F_1^v(λ^2)$ and pseudoscalar $G_P(t)$ form-factors of a nucleon are presented, where an indication of the existence of the state $π^\p$ in the range 500-800 MeV (possibly the first radial excitation of pion) is obtained, and the coupling constant of this new state with the nucleon is estimated.

hep-ph↗

arXiv1998

Effective quark model with chiral U(3)XU(3) symmetry for baryon octet and decuplet

We suggest an effective quark model for low-lying baryon octet and decuplet motivated by QCD with a linearly rising confinement potential incorporating the extended Nambu-Jona-Lasinio (ENJL) model with linear realization of chiral U(3)XU(3) symmetry. Baryons are considered as external heavy states coupled to local three-quark currents with fixed spinorial structure and to low-lying mesons through quark-meson interactions defined in the ENJL--model. In the constituent quark loop representation we have calculated the coupling constants of the (pi NN), (pi N Delta) and (gamma N Delta) interactions and the (sigma_{πN})-term. The obtained results are in reasonable agreement with experimental data and other effective field theory approaches.

hep-ph↗

arXiv1998

Scalar mesons in the Nambu--Jona-Lasinio model with 't Hooft interaction

We calculate the mass spectra of the pseudoscalar and scalar meson nonets in the Nambu--Jona-Lasinio model with the 't Hooft interaction. We obtain satisfactory result for the pseudoscalar mesons. For the scalar mesons, the 't Hooft interaction somewhat increases the values of the masses. However, it is not sufficient to explain the whole scalar mass spectrum. The situation could be improved for the $σ$ and $f_0$ mesons through mixing with the glueball state. For the description of the masses of $a_0$ and $\kstar$ mesons, it is necessary to involve the other models. The strong decay widths of the scalar mesons are described.

hep-ph↗

arXiv1997

Excited pions, rho- and omega-mesons and their decays in a chiral SU(2) x SU(2) Lagrangian

A chiral SU(2) x SU(2) Lagrangian containing, besides the usual meson fields, their first radial excitations is considered. The Lagrangian is derived by bosonization of the Nambu-Jona-Lasinio quark model with separable non-local interactions, with form factors corresponding to 3-dimensional ground and excited state wave functions. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the pions, rho-and omega-mesons are described with the help of two form factors. The weak decay constant F_pi' is calculated. The values for the decay widths of the processes rho -> 2 pi, pi' -> rho pi, rho' -> 2 pi, rho' -> omega pi and omega' -> rho pi are obtained in agreement with the experimental data.

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arXiv1993

Spontaneous Breaking of Chiral Symmetry as a Consequence of Confinement

We show that at the leading order in the large-$N$ expansion a lattice QCD motivated linear rising confinement potential at large distances leads to a non-local four-quark interaction that realizes spontaneous breaking of chiral symmetry (SBCS) in the same way the Nambu-Jona-Lasinio model does. The dynamical quark mass $m$, which represents the solution of the gap-equation, is proportional to the square root of the string tension $σ$ and takes the form at the leading order in the large-$N$ expansion $m=2 \sqrtσ/π$ with $σ=0.27$ GeV$^2$. The Nambu-Jona-Lasinio phenomenological constant $G_1$, which is responsible for SBCS, is expressed in terms of the string tension and the confinement radius.

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