Quantizing a relativistic free-particle on the light front: some subtle aspects

We use the light-front machinery to study the behavior of a relativistic free particle and obtain the quantum commutation relations from the classical Poisson brackets. We argue that their usual projection onto the light-front coordinates from the covariant commutation relations show that there is an inconsistency in the expected correlation between canonically conjugate variables time x(+) and energy p(-). This incompatibility between canonical conjugate variables in the light front is discussed in the context of Poisson brackets and a suggestion is made on how to avoid it.

A possible way to relate the covariantization and the negative dimensional integration method in the light-cone gauge

Here we present a possible way to relate the method of covariantizing the gauge-dependent pole and the negative dimensional integration method for computing Feynman integrals pertinent to the light-cone gauge fields. Both techniques are applicable to the algebraic light-cone gauge and dispense with prescriptions to treat the characteristic poles.

Modeling of organic light-emitting diodes with graded concentration in the emissive multilayer

We model the electrical behavior of organic light-emitting diodes whose emissive multilayer is formed by blends of an electron transporting material, tris-(8-hydroxyquinoline) aluminum (Alq(3)) and a hole transporting material, N,N-'-diphenyl-N,N-'-bis(1,1(')-biphenyl)-4,4-diamine. The multilayer is composed of layers of different concentration. The Alq(3) concentration gradually decreases from the cathode to the anode. We demonstrate that these graded devices have higher efficiency and operate at lower applied voltages than devices whose emissive layer is made of nominally homogeneous blends. Our results show an important advantage of graded devices, namely, the low values of the recombination rate distribution near the cathode and the anode, so that electrode quenching is expected to be significantly suppressed in these devices. (C) 2004 American Institute of Physics.

Light-front model of the kaon electromagnetic current

The kaon electromagnetic form factor is extracted from both components of the current: J(+) and J(-) with a pseudo-scalar coupling of the quarks to the meson. The pair production process does not contribute to J(+) in the Drell-Yan frame (q(+) = 0). However, the pair production process contribution is different from zero in J(-) and this contribution is necessary to keep the rotational symmetry properties of the current.

Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model

We study the scaling of the S-3(1)-S-1(0) meson mass splitting and the pseudoscalar weak-decay constants with the mass of the meson, as seen in the available experimental data. We use an effective light-front QCD-inspired dynamical model regulated at short distances to describe the valence component of the pseudoscalar mesons. The experimentally known values of the mass splitting, decay constants (from global lattice-QCD averages) and the pion charge form factor up to 4 [GeV/c](2) are reasonably described by the model.

Timelike and spacelike hadron form factors, Fock state components and light-front dynamics

A unified description of spacelike and timelike hadron form factors within a light-front model was successfully applied to the pion. The model is extended to the nucleon to study the role of qq pair production and of nonvalence components in the nucleon form factors. Preliminary results in the spacelike range 0 <= Q(2) <= 10 (GeV/c)(2) are presented.

Cosmological constant and the speed of light

By exploring the relationship between the propagation of electromagnetic waves in a gravitational field and the light propagation in a refractive medium, it is shown that, in the presence of a positive cosmological constant, the velocity of light will be smaller than its special relativity value. Then, restricting again to the domain of validity of geometrical optics, the same result is obtained in the context of wave optics. It is argued that this phenomenon and the anisotropy in the velocity of light in a gravitational field are produced by the same mechanism.

Stabilization of a light bullet in a layered Kerr medium with sign-changing nonlinearity

Using the numerical solution of the nonlinear Schrodinger equation and a variational method, it is shown that (3+1)-dimensional spatiotemporal optical solitons, known as light bullets, can be stabilized in a layered Kerr medium with sign-changing nonlinearity along the propagation direction.

Variational fits to the lattice energy of heavy-light mesons

We perform variational calculations of heavy-light meson masses using a fitted formula to a lattice two-quark potential. We examine the light quark mass dependence of the meson mass using the Schrodinger equation and the Dirac equation. For the Dirac equation, a saddle-point variational principle is employed, since the Dirac Hamiltonian is not bound from below.

Spacelike and timelike pion electromagnetic form factor and Fock state components within the light-front dynamics

The simultaneous investigation of the pion electromagnetic form factor in the space- and timelike regions within a light-front model allows one to address the issue of nonvalence components of the pion and photon wave functions. Our relativistic approach is based on a microscopic vector-meson-dominance model for the dressed vertex where a photon decays in a quark-antiquark pair, and on a simple parametrization for the emission or absorption of a pion by a quark. The results show an excellent agreement in the space like region up to -10 (GeV/c)(2), while in timelike region the model produces reasonable results up to 10 (GeV/c)(2).

Light deflection and quadratic gravity

We study the bending of light caused by a static gravitational field generated by a localized material source in the context of quadratic gravity. Our calculation shows that for light rays passing close to the Sun the deflection Phi lies in the interval 0 < < 1.75. A tree-level approach to the same issue tells us that the vacuum concerning quadratic gravity is a dispersive medium. Nom Phi is energy dependent and ranges from 0(+) to 1.75(-) arcsec.

Structure of large two-neutron halos in light exotic nuclei

The structure of three-body halo nuclei formed by two neutrons and a core (nnc) is studied using zero-range interactions. The halo wave function can be completely parameterized only by the s-wave scattering lengths and two-neutron separation energy. The sizes and the neutron-neutron correlation function of Li-11 and Be-14 are calculated and compared to experimental data. A general classification scheme for three-body halos with two identical particles is discussed as well as the critical conditions to allow excited Efimov states.

A constraint on the x dependence of the light antiquarks ratio

We perform a careful study on the effect of the Pauli blocking to the light antiquark structure of the proton sea. We develop the formal expressions for the antiquark distributions, highlighting the role played by quark statistics and the vacuum structure. Ratios involving the antiquarks are calculated. In particular, it is found that Delta(d) over bar (x)/Delta(u) over bar (x) should be negative and x independent. (C) 2002 Elsevier B.V. B.V. All rights reserved.

The kaon electromagnetic form factor in the light-front formalism

Numerical calculations are performed and compared to the experimental data for the electromagnetic form factor of the kaon, extracted from both components of the electromagnetic current, J(+) and J(-), with a pseudo-scalar coupling of the quarks to the kaon. In the case of J(+), there is no pair term contribution in the Drell-Yan frame (q(+) = 0). However, for J-, the pair term contribution is different from zero and is necessary in order to preserve the rotational symmetry of the current. The free parameters are the quark masses and the regulator mass.