arXiv subjects

M. K. Volkov

Publications and source records attributed to M. K. Volkov.

At least 109 records · Page 6Linked to original sources

arXiv2003

SU(2)xSU(2) nonlocal quark model with confinement

The nonlocal version of the SU(2)xSU(2) symmetric four-quark interaction of the NJL type is considered. Each of the quark lines contains the form factors. These form factors remove the ultraviolet divergences in quark loops. The additional condition on quark mass function m(p) ensures the absence of the poles in the quark propagator(quark confinement). The constituent quark mass m(0) is expressed thought the cut-off parameter Lambda, m(0)=Lambda=340 MeV in the chiral limit. These parameters are fixed by the experimental value of the weak pion decay and allow us to describe the mass of the light scalar meson, strong decay rho -> pi pi and D/S ratio in the decay a_1 -> rho pi in satisfactory agreement with experimental data.

hep-ph↗

arXiv2003

Pion damping width from SU(2) x SU(2) NJL model

Within the framework of the NJL model, we investigate the modification of the pion damping width in a hot pion gas for temperatures ranging from 0 to 180 MeV. The pion is found to broaden noticeably at T > 60 MeV. Near the chiral phase transition T ~ 180 MeV, the pion width is saturated and amounts to 70 MeV. The main contribution to the width comes from pion-pion collisions. Other contributions are found negligibly small.

nucl-th↗

arXiv2003

Coexistence of color superconductivity and chiral symmetry breaking within the NJL model

The phase diagram for quark matter is investigated within a simple Nambu-Jona-Lasinio model without vector correlations. It is found that the phase structure in the temperature-density plane depends sensitively on the parametrization of the model. We present two schemes of parametrization of the model where within the first one a first order phase transition from a phase with broken chiral symmetry to a color superconducting phase for temperatures below the triple point at T_t= 55 MeV occurs whereas for the second one a second order phase transition for temperatures below T_t = 7 MeV is found. In the latter case, there is also a coexistence phase of broken chiral symmetry with color superconductivity, which is a new finding within this class of models. Possible consequences for the phenomenology of the QCD phase transition at high baryon densities are discussed.

hep-ph↗

arXiv2002

Process gamma* gamma -> sigma at large virtuality of gamma*

The process gamma* gamma -> sigma is investigated in the framework of the SU(2)xSU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of gamma* in the Euclidean kinematic domain. The asymptotic behaviour of this form factor resembles the asymptotic behaviour of the gamma* gamma -> pi form factor.

hep-ph↗

arXiv2002

Sigma-meson in hot and dense matter

An important role of the scalar isoscalar sigma-meson in the low-energy physics is discussed. The behavior of the sigma-meson in the hot and dense medium is studied. It is shown that in the vicinity of critical values of temperature(T) and chemical potential(m) the sigma-meson can become a sharp resonance. This effect can lead to a strong enhancement of the processes pi pi -> gamma gamma and pi pi-> pi pi near the two-pion threshold. Experimental observation of this phenomenon can be interpreted as a signal of approaching the domain where the chiral symmetry restoration and phase transition of the hadron matter into quark-gluon plasma take place.

hep-ph↗

arXiv2002

Transition form factors and light-cone distribution amplitudes of pseudoscalar mesons in the chiral quark model

It is shown that a chiral quark model of the Nambu--Jona-Lasinio type can be used to describe "soft"-momenta parts of the amplitudes with large momentum transfer. As a sample, the processes γ^* --> γ(π,η,η') where one of the photons, γ^*, has large space-like virtuality is investigated. The γ^* --> γ(π,η,η')$ transition form factors are calculated for a wide region of transferred momenta. The results are consistent with the calculations performed in the instanton-induced chiral quark model and agree with experimental data. The distribution amplitudes of pseudoscalar mesons are derived.

hep-ph↗

arXiv2001

Chiral quark model with infrared cut-off for the description of meson properties in hot matter

A simple chiral quark model of the Nambu--Jona-Lasinio (NJL) type with a quark confinement mechanism is constructed for the description of the light meson sector of QCD at finite temperature. Unphysical quark production thresholds in the NJL model are excluded by an infrared cut-off in the momentum integration within quark loop diagrams. This chiral quark model satisfies the low energy theorems. Using the vacuum masses and decay widths of π- and ρ-mesons for fixing the model parameters, the properties of the σ- meson are derived. Within the Matsubara formalism, the model is systematically extended to finite temperatures where chiral symmetry restoration due to a dropping constituent quark mass entails a vanishing of the infrared cut-off (deconfinement) at the pion Mott temperature T_c=186 MeV. Besides of the pion mass and weak decay constant, the masses, coupling constants and decay widths of σ- and ρ-mesons in hot matter are investigated. The quark-antiquark decay channel of the light mesons is opened for T>T_c only and becomes particularly strong for the ρ- meson. The two-pion decay channel below T_c has almost constant width for the ρ- meson up to T_c, but for the σ-meson it closes below T_c such that a scalar meson state with vanishing width is obtained as a precursor of the chiral/deconfinement transition.

hep-ph↗

arXiv2001

Ground and excited scalar isoscalar meson states in a U(3)xU(3) quark model with a glueball

Ground and first radially excited scalar isoscalar meson states and a scalar glueball are described in a nonlocal U(3)xU(3) quark model. The glueball is introduced into the effective meson Lagrangian by means of the dilaton model on the base of the scale invariance of the meson Lagrangian. The scale invariance breaking by current quark masses and gluon anomalies is taken into account. The glueball anomalies turn out to be important for the description of the glueball-quarkonia mixing. The masses of five scalar isoscalar meson states and their strong decay widths are calculated. The state f_0(1500) is shown to be composed mostly of the scalar glueball.

hep-ph↗

arXiv2000

Strong Decays of Scalar Glueball in a Scale-Invariant Chiral Quark Model

An effective meson Lagrangian including a scalar glueball is constructed on the base of $U(3)\times U(3)$ chiral symmetry. The glueball is introduced into the meson Lagrangian by using the principle of scale invariance of an effective Lagrangian and the dilaton model. The singlet-octet mixing of scalar meson states is described by means of 't Hooft interaction. The contribution of the scalar and pseudoscalar anomalies into the breaking of scale invariance is taken into account. The mixing of quarkonia with the glueball is described. The mass spectrum of scalar mesons together with the glueball and also their strong decay widths are calculated. From comparing the obtained results with experimental data, it follows that $f_0(1500)$ is rather a glueball, whereas $f_0(1710)$ is a quarkonium. This accords with the results obtained in our previous works where radially-excited scalar meson states were described. It is shown that $ρ$-mesons play an important role in the description of glueball decays.

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.

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.

hep-ph↗

arXiv1999

Radially excited scalar, pseudoscalar, and vector meson nonets in a chiral quark model

A chiral Lagrangian containing, besides the usual meson fields, their first radial excitations is constructed. The Lagrangian is derived by bosonization of a Nambu--Jona-Lasinio (NJL) type quark model with separable nonlocal interactions. The nonlocality is described by form factors corresponding to 3-dimensional excited state wave functions. The spontaneous breaking of chiral symmetry is governed by the standard NJL gap equations. A simple SU(2)xSU(2) version of the model is used to demonstrate all low-energy theorems to hold valid in the chiral limit. A more realistic U(3)xU(3) model with 't Hooft interaction is constructed to describe the mass spectrum of excited scalar, pseudoscalar, and vector mesons. On the basis of global chiral symmetry, we use the same form factors for the scalar and pseudoscalar mesons. Having fixed the form factor parameters by masses of pseudoscalar mesons, we predict the mass spectrum of scalar mesons. This allows us to interpret experimentally observed scalar, pseudoscalar, and vector meson states as members of quark-antiquark nonets. It is shown that the a_0(1450), K^*_0(1430), f_0(1370), f_J(1710) scalar meson states are the first radial excitations of the ground states: a_0(980), K^*_0(960), f_0(400-1200), f_0(980). The weak decay constants F_π, F_{π'}, F_K, F_{K'} and the main strong decay widths of the scalar, pseudoscalar, and vector meson nonets are calculated.

hep-ph↗

arXiv1999

Radial excitations of scalar and η, η' mesons in a chiral quark model

First radial excitations of the scalar meson nonet and pseudoscalar mesons η, η' are described in a nonlocal chiral quark model of the Nambu--Jona-Lasinio type with 't Hooft interaction. In this model simple form factors are used, which allows us to describe first radial excitations of the mesons and to conserve the gap equations describing spontaneous breaking of chiral symmetry in the standard form. The external parameters of form factors are fixed by masses of excited pseudoscalar mesons and the same form factors are used for predicting the masses of excited scalar mesons. Strong decays of excited scalar mesons and η, η' mesons are described in satisfactory agreement with experiment.

hep-ph↗

arXiv1999

Excited scalar mesons in a chiral quark model

First radial excitations of the isoscalar and isovector scalar mesons f_0(400-1200), f_0(980) and a_0(980) are investigated in the framework of a nonlocal version of a chiral quark model of the Nambu--Jona-Lasinio type. It is shown that f_0(1370), f_J(1710) and a_0(1450) are the first radially excited states of f_0(400-1200), f_0(980) and a_0(980) which are ground states of the scalar meson nonet. The mesons' masses and strong decay widths are calculated. The scalar resonance f_0(1500) is supposed to be a glueball. The status of K_0^*(1430) is discussed.

hep-ph↗

arXiv1998

NJL model with infrared confinement

We consider an extended Nambu--Jona-Lasinio (NJL) model for the light meson sector of QCD where unphysical quark production thresholds are excluded by an infrared cut-off on the momentum integration within quark loop diagrams. This chiral quark model conserves the low energy theorems. The infrared cut-off is fixed selfconsistently by the dynamically generated quark mass (quark condensate). The masses and decay widths of the σ- and ρ-mesons are described in the model.

hep-ph↗

arXiv1998

Decays of excited strange mesons in the extended NJL model

A chiral U(3)xU(3) 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. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the kaon, K^* and ϕare described with the help of two form factors. The values for the decay widths of the processes K^*' --> ρK, K^*' --> K^* π, K^*'--> K π, ϕ' --> K^* K, ϕ' --> KK, K' --> K ρ, K' --> K^* πand K' --> K 2πare obtained in qualitative agreement with the experimental data.

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↗

arXiv1998

Excess low energy photon pairs from pion annihilation at the chiral phase transition

The photon pair production by pion annihilation in a hot and dense medium at the chiral phase transition is investigated within a chiral quark model. As a direct consequence of this transition the $σ$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_σ(T,μ) \approx 2 M_π(T,μ)$ is fulfilled. This effect results in a strong enhancement of the cross section for the pion annihilation process $2 π\to 2 γ$ compared with the vacuum case. The calculation of the photon pair production rate as function of the invariant mass shows a strong enhancement and narrowing of the $σ$ meson resonance at threshold due to chiral symmetry restoration.

hep-ph↗