Coupling Constants Of Mesons Research Articles

Strangeness thermodynamic instabilities in hot and dense nuclear matter

We explore the presence of thermodynamic instabilities and, consequently, the realization of a pure hadronic phase transition in the hot and finite baryon density nuclear matter. The analysis is performed by means of an effective relativistic mean-field model with the inclusion of hyperons, varDelta -isobars, and the lightest pseudoscalar and vector meson degrees of freedom. The Gibbs conditions on the global conservation of baryon number and zero net strangeness in symmetric nuclear matter are required. Similarly to the liquid–gas phase transition, we show that a phase transition, characterized by mechanical instabilities (due to fluctuations on the baryon number) and chemical-diffusive instabilities (due to fluctuations on the strangeness number), can take place for a finite range of varDelta -meson coupling constants, compatible with different experimental constraints. The hadronic phase transition, which presents similar features to the quark-hadron phase transition, is characterized by different strangeness content during the mixed phase and, consequently, by a sensible variation of the strange anti-particle to particle ratios.

Strong coupling constants of doubly heavy baryons with vector mesons in QCD

Using the most general form of the interpolating current for baryons, the strong electric and magnetic coupling constants of light vector mesons rho and K^* with doubly heavy baryons are computed within the light-cone sum rules. We consider 2- and 3-particle distribution amplitudes of the aforementioned vector mesons. The obtained results can be useful in the analysis of experimental data on the properties of doubly heavy baryons conducted at LHC.

Exploratory study of χc1(4140) and like states in QCD sum rules

In this work, we chose three molecular and three diquark–antidiquark currents with the quark content cc¯ss¯ and JPC=0++,1++,2++, and estimated the masses and the meson coupling constants of the ground states coupling to these currents in the framework of QCD sum rules. In operator product expansion, we considered the terms including dimension eight, and we performed pole contribution tests carefully. According to our results, all of these currents couple to the ground states with degenerate masses which are in 10 MeV vicinity of χc1(4140). Therefore, with a QCD sum rules analysis, it is not possible to conclude that χc1(4140) has a dominant molecular or diquark–antidiquark content. However, there may be three states degenerate in mass, with positive charge conjugation and different isospins.

Adjustment of Non-linear Interaction Parameters for Relativistic Mean Field Approach by Using Artificial Neural Networks

The relativistic mean field (RMF) model with a small number of adjusted parameters has been used successfully in the last thirty years for predictions of various ground-state nuclear properties of nuclei. In this model, Dirac and Klein–Gordon like equations obtained from application of variation principle on phenomenological Lagrangian density are solved iteratively for calculations of nuclear properties of nuclei. For this purpose, parameters such as masses of considered mesons, nucleon–meson coupling constants, and self-couplings of mesons are needed and they are fitted from experimental data. Some parameter sets for RMF model introduced to correct predictions of nuclear properties of nuclei cover nuclidic chart. Besides Artificial Neural Network (ANN) method is used successfully in many field of science as in nuclear physics. ANN is known as a very powerful tool that are used when standard techniques fail to estimate the correlation between the variables. In the present study, ANN method has been employed to check its understanding capability of relations between RMF model parameters and their predictions on the ground-state binding energies of some spherical nuclei. Understanding capability of ANN method for these relations of considered nuclei has been found well. Based on this success, new non-linear parameter set for RMF model called DEFNE by us have been produced by using ANN method. Furthermore, predictions of RMF model with DEFNE parameter set for ground-state binding energies and charge radii of nuclei cover nuclidic chart have been found as in agreement with the available experimental data.

Effects of the nucleon radius on neutron stars in a quark mean field model

We study the effects of free space nucleon radius on nuclear matter and neutron stars within the framework of quark mean field model. The nucleon radius is treated self-consistently with this model, where quark confinement is adjusted to fit different values of nucleon radius. Corrections due to center-of-mass motion, quark-pion coupling, and one gluon exchange are included to obtain the nucleon mass in vacuum. The meson coupling constants that describe the behavior of many-body nucleonic system are newly-constructed by reproducing the empirical saturation properties of nuclear matter, including the recent determinations of symmetry energy parameters. Our results show that the nucleon radius in free space have negligible effects on nuclear matter equation of state and neutron star mass-radius relations, which is different from the conclusion drawn in previous studies. We further explore that the sensitivity of star radius on the nucleon radius found in earlier publications is actually from the symmetry energy and its slope.

Investigation of the Excited States in Hidden Charm Hidden Strange Sector

In this work, we studied the radial excitations of X(4140) and like states within QCD sum rules. We chose three molecular and three diquark-antidiquark currents with the quark content cc‾ss‾ and JPC = 0++, 1++, 2++, and estimated the masses and the meson coupling constants of the first excited states coupling to these currents in the framework of QCD sum rules. The ground states coupling to these currents were analyzed in a previous work and we have shown that all of these ground states have degenerate masses within 10 MeV neighborhood of exotic meson X(4140). For the excited states, the masses are not found to be degenerate. We found that scalar and tensor currents are coupling to Ds⁎D‾s⁎ threshold. However for the axial vector currents, the first excited states found to have mass compatible with X(4274), which was measured in the same decay with X(4140). Thus we conclude that X(4274) could be a radial excitation of X(4140).

Charged ρ-meson condensation in neutron stars

We extend relativistic mean-field models with hadron masses and meson–baryon coupling constants dependent on the scalar field σ, including hyperons and Δ(1232) baryons, to incorporate a possibility of the charged ρ meson condensation in neutron star matter. The influence of the ρ− condensation on the equation of state proves to be strongly model dependent. In our models of one type (KVORcut-based ones) the ρ− condensation arises by a second-order phase transition above a critical density and the maximum value of the neutron star mass diminishes only slightly. The matter composition changes more significantly. In our models of other type (MKVOR*-based ones), if the system is considered at fixed density, the ρ− condensation arises by a second-order phase transition at the baryon density n=nc,ρ(II) and at a slightly higher density n=nc,ρ(I) there occurs a first-order phase transition. In a neutron star matter starting with a density n<nc,ρ(II) there appears a region of a mixed phase, or the system is described by Maxwell construction, that results in a substantial decrease of the value of the maximum neutron star mass. Nevertheless in the models under consideration the observational constraint on the maximum neutron star mass is fulfilled. Besides, in MKVOR*-based models the appearance of the ρ− condensate is accompanied by a strong rearrangement of the matter composition. Dependence of the results on a choice of the ρ meson scaling functions for the effective ρ meson mass and coupling constants is also investigated.

Dispersion theoretical analysis of the nucleon form factors

We review the achievements of the project C.2 , that deals with a dispersion theoretical analysis of the nucleon form factors. We have analyzed the world data for the space-like and time-like form factors to extract nucleon radii and vector meson coupling constants. Our proton charge radius r P E ≃ 0.85 fm has gained prominence in the so-called proton radius puzzle, see Ref. [1]. We also have analyzed the strong energy dependence of the e + e − → pp amplitude at the nucleon-antinucleon threshold, two-photon exchange effects and isospin violation in the isovector nucleon form factors.

Strong coupling constant of negative parity octet baryons with light pseudoscalar mesons in light cone QCD sum rules

The strong coupling constants of the π and K mesons with negative parity octet baryons are estimated within the light cone QCD sum rules. It is observed that all strong coupling constants, similarly to the case for the positive parity baryons, can be described in terms of three invariant functions, where two of them correspond to the well known F and D couplings in the SU(3)f symmetry, and the third function describes the SU(3)f symmetry violating effects. We compare our predictions on the strong coupling constants of pseudoscalar mesons of negative parity baryons with those corresponding to the strong coupling constants for the positive parity baryons.

Relativistic mean-field models with scaled hadron masses and couplings: Hyperons and maximum neutron star mass

An equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. All hadron masses decrease universally with the scalar field growth, whereas meson–nucleon coupling constants can vary differently. More specifically we focus on two modifications of the KVOR model studied previously. One extension of the model (KVORcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. This can be realized if the nucleon vector–meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. The other version of the model (MKVOR) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector–meson coupling constant as function of the scalar field. A possibility of hyperonization of the matter in neutron star interiors is incorporated. Our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct Urca constraint, gravitational-baryon mass constraint for the pulsar J0737-3039B, and the constraint on the maximum mass of the neutron stars.

Compact stars in a SU(3) quark-meson model

The recent observations of the massive pulsars PSR J1614-2230 and of PSR J0348+0432 with about two solar masses implies strong constraints on the properties of dense matter in the core of compact stars. Effective models of QCD aiming to describe neutron star matter can thereby be considerably constrained. In this context, a chiral quark-meson model based on a SU(3) linear $\sigma$-model with a vacuum pressure and vector meson exchange is discussed in this work. The impact of its various terms and parameters on the equation of state and the maximum mass of compact stars are delineated to check whether pure quark stars with two solar masses are feasible within this approach. Large vector meson coupling constant and a small vacuum pressure allow for maximum masses of two or more solar masses. However, pure quark stars made of absolutely stable strange quark matter, so called strange stars, turn out to be restricted to a quite small parameter range.

Critical density and impact ofΔ(1232)resonance formation in neutron stars

The critical densities and impact of forming \D resonances in neutron stars are investigated within an extended nonlinear relativistic mean-field (RMF) model. The critical densities for the formation of four different charge states of \D are found to depend differently on the separate kinetic and potential parts of nuclear symmetry energy, the first example of a microphysical property of neutron stars to do so. Moreover, they are sensitive to the in-medium Delta mass $m_{\Delta}$ and the completely unknown $\Delta$-$\rho$ coupling strength $g_{\rho\Delta}$. In the universal baryon-meson coupling scheme where the respective $\Delta$-meson and nucleon-meson coupling constants are assumed to be the same, the critical density for the first $\Delta^-(1232)$ to appear is found to be \rc=$(2.08\pm0.02)\rho_0$ using RMF model parameters consistent with current constraints on all seven macroscopic parameters usually used to characterize the equation of state (EoS) of isospin-asymmetric nuclear matter (ANM) at saturation density $\rho_0$. Moreover, the composition and the mass-radius relation of neutron stars are found to depend significantly on the values of the $g_{\rho\Delta}$ and $m_{\Delta}$.

Interaction of antiproton with nuclei

We performed fully self-consistent calculations of $\bar{p}$-nuclear bound states within the relativistic mean-field (RMF) model. The G-parity motivated $\bar{p}$-meson coupling constants were adjusted to yield potentials consistent with $\bar{p}$-atom data. We confirmed large polarization effects of the nuclear core caused by the presence of the antiproton. The $\bar{p}$ absorption in the nucleus was incorporated by means of the imaginary part of a phenomenological optical potential. The phase space reduction for the $\bar{p}$ annihilation products was taken into account. The corresponding $\bar{p}$ width in the medium significantly decreases, however, it still remains considerable for the $\bar{p}$ potential consistent with experimental data.

Antibaryon—nucleus bound states

We calculated antibaryon bound states in selected nuclei within the relativistic mean-field (RMF) model. The G-parity motivated B̄-meson coupling constants were scaled to yield corresponding potentials consistent with available experimental data. Large polarization of the nuclear core caused by B̄ was confirmed. The p̄ annihilation in the nuclear medium was incorporated by including a phenomenological imaginary part of the optical potential. The calculations using a complex p̄-nucleus potential were performed fully self-consistently. The p̄ widths significantly decrease when the phase space reduction is considered for p̄ annihilation products, but they still remain sizeable for potentials consistent with p̄-atom data.

Equation of state with an extended SU(3) quark-meson model under conditions prevailing in core collapse supernovae

The quark-meson model is investigated for the two- and three-flavor case extended by contributions of vector mesons under conditions encountered in core-collapse supernova matter. Typical temperature ranges, densities and electron fractions, as found in core-collapse supernova simulations, are studied by implementing charge neutrality and local beta-equilibrium with respect to weak interactions. Within this framework, we analyze the resulting phase diagram and equation of state (EoS) and investigate the impact of undetermined parameters of the model. The EoS turns out to be relatively independent on the entropy per baryon but there are significant changes when going from the two-flavor to the three-flavor case due to the nontrivial contribution from the strange quarks which stay massive even at high densities. While an increasing vector meson coupling constant leads to a substantial stiffening of the EoS, we find that the impact of changing the scalar meson mass is equally strong and results in a softening of the EoS for increasing values.

QCD sum rules for the coupling constants of vector mesons to octet baryons

The QCD sum rules on the light cone proposed by Wang for the coupling constants of the ρ meson are generalized to the vector mesons ω and φ and all octet baryons, the Λ-hyperon included. A comparison with other results is given.

Spin-3/2 to spin-1/2 heavy baryons and pseudoscalar mesons transitions in QCD

The strong coupling constants of light pseudoscalar mesons with spin-3/2 and spin-1/2 heavy baryons are calculated in the framework of light cone QCD sum rules. It is shown that each class of transitions among members of the sextet spin-3/2 to sextet spin-1/2 baryons and that of the sextet spin-3/2 to spin-1/2 anti-triplet baryons is described by only one invariant function. We also estimate the widths of kinematically allowed transitions. Our results on decay widths are in good agreement with the existing experimental data, as well as predictions of other nonperturbative approaches.

Strong coupling constants of light pseudoscalar mesons with heavy baryons in QCD

We calculate the strong coupling constants of light pseudoscalar mesons with heavy baryons within the light cone QCD sum rules method. It is shown that sextet–sextet, sextet–antitriplet and antitriplet–antitriplet transitions are described by one universal invariant function for each class. A comparison of our results on the coupling constants with the predictions existing in literature is also presented.

Mesons and nucleons from holographic QCD in a unified approach

We investigate masses and coupling constants of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. We first examine an appropriate form of fermionic solutions by restricting the mass coupling for the five dimensional bulk fermions and bosons. We then derive approximated analytic solutions for the nucleons and the corresponding masses in a small mass coupling region. In order to treat meson and nucleon properties on the same footing, we introduce the same infrared (IR) cut in such a way that the meson-nucleon coupling constants, i.e., gπNN and gρNN are uniquely determined. The first order approximation with respect to a dimensionless expansion parameter, which is valid in the small mass coupling region, explicitly shows difficulties to avoid the IR scale problem of the hard wall model. We discuss possible ways of circumventing these problems.

Vector meson-baryon strong coupling constants in light cone QCD sum rules

Using the most general form of the interpolating current of the baryons, the strong coupling constants of the light vector mesons with the octet baryons are calculated within the light cone QCD sum rules. The $SU(3{)}_{f}$ symmetry breaking effects are taken into account in the calculations. It is shown that each of the electric and magnetic coupling constants can be described in terms of three universal functions. A detailed comparison of the results of this work on aforementioned couplings with the existing theoretical results is presented.