Quark Mass Dependence of Nucleon Magnetic Moment and Charge Radii

Understanding hadron structure within the framework of QCD is an extremely challenging problem. Our purpose here is to explain the model-independent consequences of the approximated chiral symmetry of QCD for two famous results concerning the quark structure of the nucleon. We show that both the apparent success of the constituent quark model in reproducing the ratio of proton to neutron magnetic moments and the apparent success of the Foldy term in reproducing the observed charge radius of the neutron are coincidental. That is, a relatively small change of the current quark mass would spoil both results.     

Symmetry dependence of rms Charge Radii

The nucleon number dependence of rms charge radii is often approximated by some simple formula containing the mass number only, R(A)=r(A)A^1/3, where r(A) is a slowly varying function of A. However, for nuclei off the stability line, the mass number A=N + Z is not enough to characterise the dependence of the R(Z, N) radius surface on the nucleon numbers Z and N. In the present work, an additional term has been included, depending on the symmetry parameter I=(N ? Z)/A. Several parametrisations were tried, using weighted least-squares procedures for the fit to a present-day data base. The best fit (with χ²/ń=17) was found for R(A, I)=r(A)A^1/3 + b_I/(I ? I_stab), where I_stab=(N_stab ? Z_stab)/A is the value of the symmetry parameter of the stable isobar with mass number A, and b_I=?0.83 fm. The formula R(A, I)=[r(A) + a_I(I ? I_stab)]A^1/3 is only slightly inferior to the previous one, moreover, it is supported by simple model calculations; here a_I=?0.20 fm (χ²/ń=20). The difficulty in determining the right parametrisation is caused by the fact that the surface R_exp(A, I) is not smooth: there are strong shell and deformation effects. To avoid the distorting effect of these deviations on the parameter values, more than half of the original data had to be omitted.     

Anomaly in the Charge Radii and Nuclear Structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of the kink in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.     

Charge Radii of Tin Isotopes and Their Proton-Density Distributions within the Dispersive Optical Model

Proton single-particle properties of even–even tin isotopes in the mass number range between 100 and 132 were calculated on the basis of the dispersive optical model. The possibility of describing data on the charge radius $$r_{mathrm{ch}}$$ was studied. A decrease in the rate of growth of $$r_{mathrm{ch}}$$ with increasing $$N$$ in the region of $$N>76$$ was obtained via increasing the energy interval in the vicinity of $$E_{mathrm{F}}$$ where the imaginary part of the potential used is close to zero. The predictive power of the dispersive optical model for the density distribution in nuclei far from the beta-stability valley was demonstrated.     

Charge Radii of Argon Isotopes in the f7/2 Shell and Radii Systematics in the Ca-Region

Changes in mean square (ms) nuclear charge radii of Ar isotopes across the 1f_7/2 shell are studied by fast-beam collinear laser spectroscopy using an ultra-sensitive detection method based on optical pumping and state-selective collisional ionization. The new data set on Ar, in combination with the known charge radii of K, Ca and Ti in the ν1f_7/2 shell, offers an opportunity to obtain a more complete overview of nuclear radii trends around the proton shell closure Z = 20 and between the neutron shell closures N = 20 and N = 28.     

Higher Dimensional Cosmological Model with Quark and Strange Quark Matter

We study higher dimensional homogeneous cosmological model in the presence of quark and strange quark matter. The dynamical behavior of the model for the strange quark matter equation of state of the form p = \frac13 (r- 4 B_c)p= \frac{1}{3} (\rho- 4 B_{c}) are studied.     

The Leading-Order Charm Quark Contribution to the Next-to-Leading-Order Proton Structure Function Using {\cal A}=3 Mirror Nuclei as Input Valence Quarks

The charm quark contribution to the proton structure function (SF) is investigated in the leading-order (LO) QCD at small x region. A next-to-leading order (NLO) QCD analysis for the proton SF is made within the renormalization scheme of the radiation parton evolution model (DGLAP). The valence quark distribution is obtained from the relativistic quark-exchange calculation for the mirror nuclei, i.e., ³He and ³H, which is based on a realistic model. The inverse Mellin technique is performed to extract the parton distribution in the (x, Q ²)-plane. The calculated F ₂ ^c (x, Q ²) and F ₂ ^p (x, Q ²) as well as the longitudinal SF, F _L ^p (x, Q ²) are compared with the experimental data available at present, namely H1, ZEUS, and HERMES at HERA ring as well as other theoretical models, especially the hard pomeron phenomenological model.     

Relativistic Coupled-Channel Quark Model for Meson Resonances

We present results from a study of meson ground and resonant states within a relativistic coupled-channel constituent-quark model. Along such an approach in particular the resonance character of hadron excitations can be fully taken into account. Thus it becomes possible to describe the decay of a hadron resonance into a lower lying state more realistically than in usual single-channel approaches. In a simplified model we demonstrate the viability and the advantages of our method by producing relativistic invariant results for the finite decay width of a meson resonance.     

Recent Results for the Unquenched Quark Model

We discuss a new generation of unquenched quark models for baryons is presented in which the effects of quark–antiquark pairs are taken into account in an explicit form by means of a ³ P ₀ quark–antiquark creation mechanism. This provides the possibility to address many open problems in baryons structure and spectroscopy. The applications to magnetic moments and to the spin and flavor content of baryons will be reviewed here.     

A Relativistic Model for Strange Quark Star

We propose a relativistic model for strange quark stars within the framework of MIT Bag model. In our model, we assume that the highly compact strange stars are anisotropic in nature which is an expected feature in the ultra high density regime. We discuss various physical features of the model and show that the model satisfies all the regularity conditions. By estimating the value of the Bag constant for strange star candidates like 4U 1820-30, Her X-1 and SAX J 1808.4-3658, we show that a wire range of values of the Bag constant are possible for such stars though, in the case of 4U 1820-30, the estimated value of the Bag constant has been found to be very close to its currently acceptable range. Nevertheless, our results are in agreement with the recent CERN-SPS and RHIC data.     

A Gaussian Model for Anisotropic Strange Quark Stars

For studying the anisotropic strange quark stars,we assume that the radial pressure inside an anisotropic star can be obtained simply by isotropic pressure plus an additional Gaussian term with three free parameters(A,μand χ).According to recent observations,a pulsar in a mass range of 1.97±0.04M_⊙ has been measured.Hence,we take this opportunity to set the free parameters of our model.We fix χ by applying boundary and stability conditions and then search the A —μ parameter space for a maximum mass range of 1.9M_⊙ M_(max) 2.1M_⊙.Our results indicate that anisotropy increases the maximum mass M_(max) and also its corresponding radius R for a typical strange quark star.Furthermore,our model shows magnetic field and electric charge increase the anisotropy factor △.In fact,△ has a maximum on the surface and this maximum goes up in the presence of magnetic field and electric charge.Finally,we show that anisotropy can be more effective than either magnetic field or electric charge in raising maximum mass of strange quari stars.     

Mesons in the Constituent Quark Model

The quark-antiquark （q^-q） spectrum is studied by solving the Schrōdinger equation in the framework of nonrelativistic constituent quark model. An overall good fit to the experimental data of meson is obtained. The interactions between quark and antiquark consist of quadratic colour confinement-exchange, one-gluon-exchange, and Goldstone-boson-exchange potentials.     

A Vector-Field Model of Valence and Radiation

Abstract

One of the most baffling questions of chemistry is: Why does water have a dipole moment?     

Nucleon Spin Content in a Relativistic Quark Potential Model Approach

Based on a relativistic quark model approach with an effective potential U(r) = (ac/2)(1 + γ0)r2, the spin content of the nucleon is investigated. Pseudo-scalar interaction between quarks and Goldstone bosons is employed to calculate the couplings between the Goldstone bosons and the nucleon. Different approaches to deal with the center of mass correction in the relativistic quark potential model approach are discussed.     

The Constituent Quark Exchange Model for the Bound State Nucleons

The aim of present article is to compare the different bound state parton distributions in the protons with those coming from the free protons experimental data and to investigate the effect of quark structure of protons on each other. So, the constituent quark model (CQM), in which the quarks are assumed to be the complex objects and was originally proposed by Altarelli et al. (ACMP), is used in the frame work of the quark exchange model (QEM) to calculate the parton distributions of bound protons. Unlike our previous works, the effect of sea quarks and gluons are included in the QEM. Our results are in agreement with those of Glück et al. (GRV) when we ignore the binding and the Fermi motion effects for the constituent quarks. In this case, we get more sea-quarks and gluons with respect to the bound state constituents quarks calculation. It is also shown that the QEM, which is a realistic formalism gives better result with respect to the Isgur and Karl et al. model which is a field theoretical approach. The ratio of the structure functions of neutron to proton is also calculated with the assumption of isospin symmetry and it is compared with the available data and our previous works.     

Charge Form Factor and Radii of $${}^{\mathbf{6}}$$ Li

Physics of Atomic Nuclei - In the present work, aimed to investigate the nuclear structure of $${}^{6}$$ Li, the charge form factor and the charge radius of $${}^{6}$$ Li have been calculated....