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.

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.

Four-point amplitude from open superstring field theory

An open superstring field theory action has been proposed which does not suffer from contact term divergences. In this paper, we compute the on-shell four-point tree amplitude fi om this action using the Giddings map. After including contributions from the quartic term in the action, the resulting amplitude agrees with the first-quantized prescription. (C) 2000 Elsevier B.V. B.V. All rights reserved.

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.

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).

Conformal field theory of AdS background with Ramond-Ramond flux

We review a formalism of superstring quantization with manifest six-dimensional spacetime supersymmetry, and apply it to AdS(3) x S-3 backgrounds with Ramond-Ramond flux. The resulting description is a conformal field theory based on a sigma model whose target space is a certain supergroup SU' (2\2).

Scalar field theory at finite temperature in D=2+1

We discuss the phi(6) theory defined in D=2+1-dimensional space-time and assume that the system is in equilibrium with a thermal bath at temperature beta(-1). We use the 1/N expansion and the method of the composite operator (Cornwall, Jackiw, and Tomboulis) for summing a large set of Feynman graphs. We demonstrate explicitly the Coleman-Mermin-Wagner theorem at finite temperature.

Duality in noncommutative topologically massive gauge field theory revisited

We introduce a master action in non-commutative space, out of which we obtain the action of the non-commutative Maxwell-Chern-Simons theory. Then, we look for the corresponding dual theory at both first and second order in the non-commutative parameter. At the first order, the dual theory happens to be, precisely, the action obtained from the usual commutative self-dual model by generalizing the Chern-Simons term to its non-commutative version, including a cubic term. Since this resulting theory is also equivalent to the non-commutative massive Thirring model in the large fermion mass limit, we remove, as a byproduct, the obstacles arising in the generalization to non-commutative space, and to the first non-trivial order in the non-commutative parameter, of the bosonization in three dimensions. Then, performing calculations at the second order in the non-commutative parameter, we explicitly compute a new dual theory which differs from the non-commutative self-dual model and, further, differs also from other previous results and involves a very simple expression in terms of ordinary fields. In addition, a remarkable feature of our results is that the dual theory is local, unlike what happens in the non-Abelian, but commutative case. We also conclude that the generalization to non-commutative space of bosonization in three dimensions is possible only when considering the first non-trivial corrections over ordinary space.

Scalar field theory at finite temperature in D=2+1

We discuss the phi(6) theory defined in D = 2 + 1-dimensional space-time and assume that the system is in equilibrium with a thermal bath at temperature beta(-1). We use the 1/N expansion and the method of composite operator (CJT) for summing a large set of Feynman graphs. We demonstrate explicitly the Coleman-Mermin-Wagner theorem at finite temperature.

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.

Generating Erler-Schnabl-type solution for the tachyon vacuum in cubic superstring field theory

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Regularizing cubic open Neveu-Schwarz string field theory

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Light Front Boson Model Propagation

The scope and aim of this work is to describe the two-body interaction mediated by a particle (either the scalar or the gauge boson) within the light-front formulation. To do this, first of all we point out the importance of propagators and Green functions in Quantum Mechanics. Then we project the covariant quantum propagator onto the light front time to get the propagator for scalar particles in these coordinates. This operator propagates the wave function from x(+) = 0 to x(+) > 0. It corresponds to the definition of the time ordering operation in the light front time x(+). We calculate the light-front Green's function for 2 interacting bosons propagating forward in x(+). We also show how to write down the light front Green's function from the Feynman propagator and finally make a generalization to N bosons.