arXiv subjects

A. E. Radzhabov

Publications and source records attributed to A. E. Radzhabov.

36 records · Page 2Linked to original sources

arXiv2008

Aspects of the phase diagram in (P)NJL-like models

We discuss three applications of NJL- and PNJL-like models to assess aspects of the QCD phase diagram: First, we study the effect of mesonic correlations on the pressure below and above the finite temperature phase transition within a nonlocal PNJL model beyond the mean-field approximation. Second, we reconstruct the phase boundary of an NJL model from a Taylor expansion of the chiral susceptibility about $μ= 0$ and compare the result with the exact phase boundary. Finally, we demonstrate the realization of the "non-standard scenario" for the critical surface in a three-flavor PNJL model with a $μ$-dependent determinant interaction.

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arXiv2008

Effects of mesonic correlations in the QCD phase transition

The finite temperature phase transition of strongly interacting matter is studied within a nonlocal chiral quark model of the NJL type coupled to a Polyakov loop. In contrast to previous investigations which were restricted to the mean-field approximation, mesonic correlations are included by evaluating the quark-antiquark ring sum. For physical pion masses, we find that the pions dominate the pressure below the phase transition, whereas above T_c the pressure is well described by the mean-field approximation result. For large pion masses, as realized in lattice simulations, the meson effects are suppressed.

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arXiv2007

$η$ and $η'$ mesons in the Dyson-Schwinger approach at finite temperature

We study the temperature dependence of the pseudoscalar meson properties in a relativistic bound-state approach exhibiting the chiral behavior mandated by QCD. Concretely, we adopt the Dyson-Schwinger approach with a rank-2 separable model interaction. After extending the model to the strange sector and fixing its parameters at zero temperature, T=0, we study the T-dependence of the masses and decay constants of all ground-state mesons in the pseudoscalar nonet. Of chief interest are $η$ and $η^\prime$. The influence of the QCD axial anomaly on them is successfully obtained through the Witten-Veneziano relation at T=0. The same approach is then extended to T>0, using lattice QCD results for the topological susceptibility. The most conspicuous finding is an increase of the $η^\prime$ mass around the chiral restoration temperature $T_{\rm Ch}$, which would suggest a suppression of $η^\prime$ production in relativistic heavy-ion collisions. The increase of the $η^\prime$ mass may also indicate that the extension of the Witten-Veneziano relation to finite temperatures becomes unreliable around and above $T_{\rm Ch}$. Possibilities of an improved treatment are discussed.

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arXiv2007

rho(omega)-> pi^0 pi^0 gamma, rho(omega) -> eta pi^0 gamma decays in the local quark Nambu--Jona-Lasinio model

The branching ratios and photon spectra of the rare processes rho(omega)-> pi^0 pi^0 gamma, rho(omega) -> eta pi^0 gamma are calculated in the framework of the standard local quark Nambu--Jona-Lasinio (NJL) model. Three types of diagrams are considered: the quark box and the pole diagrams with scalar (sigma,a_0(980)) and vector (rho,omega) mesons. The obtained estimations for the widths of the processes rho(omega)-> pi^0 pi^0 gamma are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes rho(omega) -> eta pi^0 gamma.

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arXiv2007

Separable Dyson-Schwinger model at zero and finite T

Theoretical understanding of experimental results from relativistic heavy-ion collisions requires a microscopic approach to the behavior of QCD n-point functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger equations, properly generalized within the Matsubara formalism. The technical complexity of related finite-temperature calculations however mandates modeling. We present a model where the QCD interaction in the infrared, nonperturbative domain, is modeled by a separable form. Results for the mass spectrum of light quark flavors at finite temperature are presented.

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arXiv2007

Pseudoscalar Meson Nonet at Zero and Finite Temperature

Theoretical understanding of experimental results from relativistic heavy-ion collisions requires a microscopic approach to the behavior of QCD n-point functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger equations, properly generalized within the Matsubara formalism. The convergence of sums over Matsubara modes is studied. The technical complexity of finite-temperature calculations mandates modeling. We present a model where the QCD interaction in the infrared, nonperturbative domain, is modeled by a separable form. Results for the mass spectrum of light quark flavors (u, d, s) and for the pseudoscalar bound-state amplitudes at finite temperature are presented.

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arXiv2006

Process eta -> pi^0 gamma gamma in the Nambu-Jona-Lasinio model

The decay width of the process eta -> pi^0 gamma gamma is calculated in the framework of the Nambu-Jona-Lasinio model. The momentum dependence of quark loops is taken into account. Three types of diagrams are considered: quark box, scalar(a0) and vector(rho, omega) pole diagrams. The obtained estimations are in satisfactory agreement with recent experimental data.

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arXiv2006

pi pi scattering in a nonlocal Nambu -- Jona-Lasinio model

We consider a nonlocal version of the Nambu and Jona-Lasinio model. The nonlocality is contained in the quark-antiquark bilinears of the four-quark vertices as a form factor of the Gaussian type. The model has three parameters which can be fixed in favour of the values of the pion mass, the pion decay constant f_pi, and the current quark mass. The pi pi scattering amplitude is obtained by calculating the quark box and the sigma-pole diagrams, where sigma is the scalar isoscalar meson. It is shown that this amplitude satisfies the well-known Weinberg relation. We obtain the s, p, d wave scattering lengths in all isotopic channels and the s wave slope parameters. The results are in satisfactory agreement with both phenomenological data and the basic requirements of low-energy theorems, thus supporting to the form factor used.

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arXiv2005

Scalar sigma meson at finite temperature in nonlocal quark model

Properties and temperature behavior of pi and sigma bound states are studied in the framework of the nonlocal model with a separable interaction kernel based on the quark Dyson-Schwinger and the meson Bethe-Salpeter equations. M_pi(T), f_pi(T), M_sigma(T) and Gamma_{sigma -> pi pi}(T) are considered above and below the deconfinement and chiral restoration transitions.

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arXiv2005

Two-photon decays of vector mesons and dilepton decays of scalar mesons in dense matter

Two-photon decays of vector mesons and dilepton decays of scalar mesons which are forbidden in vacuum and can occur in dense baryonic matter due to the explicit violation of Lorentz symmetry are described within a quark model of the Nambu--Jona-Lasinio type. The temperature and chemical potential dependence of these processes is investigated. It is found that their contribution to the production of photons and leptons in heavy-ion collisions is enhanced near the conditions corresponding to the restoration of chiral symmetry. Moreover, in the case of the a_0 meson and especially the ρ-meson, a resonant behaviour (an additional amplification) is observed due to the degeneration of ρand a_0 masses when a hot hadron matter is approaching a chirally symmetric phase.

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arXiv2005

Two-photon decays of rho and omega mesons and strong decays rho -> eta pi and omega -> pi pi in dense matter

Two-photon decays of rho and omega mesons and strong decays rho -> eta pi and omega -> pi pi are described in the quark Nambu-Jona-Lasinio(NJL) model in dense medium. Decays of rho-meson are especially interesting because they contain intermediate a_0-meson which became a sharp resonance in the vicinity of phase transition of hadron matter into quark-gluon plasma. This leads to increasing rho decay width and, as a result, two-photon decay of rho-meson in medium became comparable with two-photon decays of scalar and pseudoscalar mesons in vacuum. Similar effect take place in the strong decay rho -> eta pi.

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arXiv2005

Forty-fifth anniversary of the Nambu-Jona-Lasinio model

A short review of the development of the Nambu-Jona-Lasinio (NJL) model is given. The SU(2)x SU(2) and U(3)x U(3) local quark NJL models are considered. The mechanisms of spontaneous breaking of chiral symmetry and vector dominance are shown. The local NJL model allows us to describe the mass spectrum and main strong and electroweak decays of the four ground-state nonets of pseudoscalar, scalar, vector and axial-vector mesons. Applications of this model to the description of mesons in hot and dense medium are discussed. It is shown that for solving problems connected with the description of the meson radial excitations and quark confinement it is necessary to consider a nonlocal extension of the NJL model. The main attention is attracted to the description of the methods used in different versions of the NJL model. Physical results for low-energy hadron physics obtained in these models can be found in the cited works.

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arXiv2004

Charged pion polarizability in the nonlocal quark model of Nambu-Jona-Lasinio type

The polarizability of a charged pion is estimated in the framework of the nonlocal chiral quark model of the Nambu--Jona-Lasinio type. Nonlocality is described by quark form factors of the Gaussian type. It is shown that the polarizability in this model is very sensitive to the form of nonlocality and choice of the model parameters.

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arXiv2004

Pion radii in nonlocal chiral quark model

The electromagnetic radius of the charged pion and the transition radius of the neutral pion are calculated in the framework of the nonlocal chiral quark model. It is shown in this model that the contributions of vector mesons to the pion radii are noticeably suppressed in comparison with a similar contribution in the local Nambu--Jona-Lasinio model. The form-factor for the process gamma*pi+pi- is calculated for the -1 GeV^2<q^2<1.6 GeV^2. Our results are in satisfactory agreement with experimental data.

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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.

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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.

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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.

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arXiv2001

Unitary mixing scalar-vector in $ξ$ gauge

We study the effect of unitary mixing of scalar and vector fields in general $ξ$ gauge. This effect takes place for non-conserved vector currents and $ξ$ gauge generates some additional problems with unphysical scalar field. We obtained solutions of Dyson-Schwinger equations and perfomed the renormalization of full propagators. The key feature of renormalization is the usage of Ward identity, which relates some different Green functions. We found that using Ward identity leads to disappearing of $ξ$-dependence in renormalized matrix element.

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