The nucleon structure function and the quark effective potential

By considering a statistical model for the quark content of the nucleon, where the quark levels are generated by a Dirac equation with a harmonic scalar-plus-vector potential, we note that a good fit for the ratio between the structure functions of the neutron and proton, F-2(n)/F-2(p), can be obtained if different strengths are used for the effective confining potentials of the up and down quarks.

Vacuum polarization effects in hyperon-rich dense matter - a nonperturbative treatment

We derive the equation of state (EOS) for electrically charged neutral dense matter using the quantum hadrodynamics (QHD) model. This is carried out in a non-perturbative manner including quantum corrections for baryons through a realignment of vacuum with baryon-antibaryon condensates. This yields the results of relativistic Hartree approximation of summing over baryonic tadpole diagrams. The quantum corrections from the scalar meson is also taken into account in a similar way. This leads to a softening of the EOS for the hyperonic matter. The formalism also allows Lis to make a self-consistent calculation of the in-medium sigma meson mass. The effects of such quantum corrections on the composition of charged neutral dense matter is considered. The effect of the resulting EOS on the structure of neutron stars is also studied.

Quark clustering and chiral symmetry breaking in nuclear matter

Chiral symmetry breaking at finite baryon density is usually discussed in the context of quark matter, i.e. a system of deconfined quarks. Many systems like stable nuclei and neutron stars however have quarks confined within nucleons. In this paper we construct a Fermi sea of three-quark nucleon clusters and investigate the change of the quark condensate as a function of baryon density. We study the effect of quark clustering on the in-medium quark condensate and compare results with the traditional approach of modeling hadronic matter in terms of a Fermi sea of deconfined quarks.

Chiral-symmetry restoration in clustered hadronic matter

Chiral-symmetry restoration is usually discussed in the context of quark matter, a system of deconfined quarks. However, many systems like stable nuclei and neutron stars have quarks confined within nucleons. In the present paper we use a Fermi sea of three-quark clusters instead of a Fermi sea of deconfined quarks to investigate the in-medium quark condensate. We find that an enhancement of the chiral breaking in clustered matter as claimed in the literature is not a consequence of the clustering but rather dependent on the microscopic model dynamics.

Kinematical and nonlocality effects on the nonmesonic weak hypernuclear decay

We make a careful study about the nonrelativistic reduction of one-meson-exchange models for the nonmesonic weak hypernuclear decay. Starting from a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (pi, eta, K, rho, omega, K*), the strangeness-changing weak LambdaN --> NN transition potential is derived, including two effects that have been systematically omitted in the literature, or, at best, only partly considered. These are the kinematical effects due to the difference between the lambda and nucleon masses, and the first-order nonlocality corrections, i.e., those involving up to first-order differential operators. Our analysis clearly shows that the main kinematical effect on the local contributions is the reduction of the effective pion mass. The kinematical effect on the nonlocal contributions is more complicated, since it activates several new terms that would otherwise remain dormant. Numerical results for C-12(Lambda) and He-5(Lambda) are presented and they show that the combined kinematical plus nonlocal corrections have an appreciable influence on the partial decay rates. However, this is somewhat diminished in the main decay observables: the total nonmesonic rate, Gamma(nm), the neutron-to-proton branching ratio, Gamma(n)/Gamma(p), and the asymmetry parameter, a(Lambda). The latter two still cannot be reconciled with the available experimental data. The existing theoretical predictions for the sign of a(Lambda) in He-5(Lambda) are confirmed. (C) 2003 Elsevier B.V. All rights reserved.

On the calculation of inner products of Schur functions

Two methods for calculating inner products of Schur functions in terms of outer products and plethysms are given and they are easy to implement on a machine. One of these is derived from a recent analysis of the SO(8) proton-neutron pairing model of atomic nuclei. The two methods allow for generation of inner products for the Schur functions of degree up to 20 and even beyond.

Study of W boson production in PbPb and pp collisions at root s(NN)=2.76 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Quark sea asymmetry of the nucleon

The light anti-quark and quark distribution in the proton, as well as the neutron to proton ratio of the structure functions, extracted from experimental data, are well fitted by a, statistical model of linear-confined quarks. The parameters of the model are given by a temperature, which is adjusted by the Gottfried sum-rule violation, and two chemical potentials given by the corresponding up (u) and down (d) quark normalizations in the nucleon. The quark energy levels are generated by a relativistic linear-confined scalar plus vector potential.

IMPROVED STATISTICAL QCD MODEL FOR THE QUARK CONTENT of THE NUCLEON

The neutron-to-proton ratio of the structure functions, F(2)(n)/F(2)(p), as well as the corresponding difference F(2)(p)-F(2)(n) are obtained within a statistical quark model for the nucleon, where the quark energy levels are given by a central linear confining potential.

Universal aspects of light halo nuclei

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Quark sea structure functions of the nucleon in a statistical model

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Awaking the Vacuum in Relativistic Stars

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Universality and Halo Nuclei

Universal aspects of few-body systems will be reviewed motivated by recent interest in atomic and nuclear physics. The critical conditions for the existence of excited states in three-body systems with two-identical particles will be explored. In particular, we consider halo nuclei that can be modeled as three-body nuclear systems, with two halo neutrons and a core. In this context, we also discuss the low-energy neutron-C-19 elastic scattering, near the conditions for the appearance of an Efimov state.

A física da terapia de captura de nêutrons pelo boro

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nucleon magnetic moments in light-front models with quark mass asymmetries

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)