Light-front Frame Research Articles

Medium modification of the nucleon mechanical properties: Abel tomography case

We investigate how the gravitational form factors of the nucleon undergo changes in nuclear matter, emphasizing the Abel transformation from the three-dimensional (3D) Breit frame to the two-dimensional (2D) light-front frame. Since the gravitational form factors reveal the mechanical structure of the nucleon, we examine also the medium modifications of the energy–momentum, pressure, and shear-force distributions. We scrutinize the stabilities of the nucleon in nuclear matter. For this purpose, we employ the in-medium modified SU(2) Skyrme model to study these mechanical quantities of the nucleon, since it provides a simple but clear framework. In this in-medium modified SU(2) Skyrme model, the modification of pionic properties is performed by using low-energy pion-nucleus scattering data and the saturation properties of nuclear matter near the normal nuclear matter density, rho _0=0.5m_pi ^3. The results reveal how the nucleon swells in nuclear matter as the mass distribution of the nucleon is broadened in medium. We also show that the mean square radii corresponding to the mass and angular momentum distributions increase in nuclear medium. This feature is kept both in 3D and 2D cases. We visualize how the strong force fields inside the nucleon in the 2D plane are distributed and illustrate how these forces undergo change in nuclear matter.

D -wave effects in heavy quarkonium production in ultraperipheral nuclear collisions

The $D$-wave admixture in quarkonium wave functions is acquired from the photonlike structure of $V\to Q\bar Q$ transition in the light-front frame widely used in the literature. Such a $D$-wave ballast is not justified by any nonrelativistic model for $Q-\bar Q$ interaction potential and leads to falsified predictions for the cross sections in heavy quarkonium production in ultra-peripheral nuclear collisions. We analyze this negative role of $D$-wave contribution by comparing with our previous studies based on a simple non-photon-like "$S$-wave-only" $V\to Q\bar Q$ transition in the $Q\bar Q$ rest frame.

Quark transverse charge densities in the [formula omitted] from lattice QCD

We extend the formalism relating electromagnetic form factors to transverse quark charge densities in the light-front frame to the case of a spin-3/2 baryon and calculate these transverse densities for the Δ ( 1232 ) isobar using lattice QCD. The transverse charge densities for a transversely polarized spin-3/2 particle are characterized by monopole, dipole, quadrupole, and octupole patterns representing the structure beyond that of a pure point-like spin-3/2 particle. We present lattice QCD results for the Δ-isobar electromagnetic form factors for pion masses down to approximatively 350 MeV for three cases: quenched QCD, two-degenerate flavors of dynamical Wilson quarks, and three flavors of quarks using a mixed action that combines domain wall valence quarks and dynamical staggered sea quarks. We extract transverse quark charge densities from these lattice results and find that the Δ is prolately deformed, as indicated by the fact that the quadrupole moment G E 2 ( 0 ) is larger than the value −3 characterizing a point particle and the fact that the transverse charge density in a Δ + of maximal transverse spin projection is elongated along the axis of the spin.

Unruh effect in the general light-front frame

We study the phenomenon of Unruh effect in a massless scalar field theory quantized on the light front in the general light-front frame. We determine the uniformly accelerating coordinates in such a frame and through a direct transformation show that the propagator of the theory has a thermal character in the uniformly accelerating coordinate system with a temperature given by Tolman's law. We also carry out a systematic analysis of this phenomenon from the Hilbert space point of view and show that the vacuum of this theory appears as a thermal vacuum to a Rindler observer with the same temperature as given by Tolman's law.

Quantization in a general light-front frame

In this paper, we study the question of quantization of quantum field theories in a general light-front frame. We quantize scalar and fermion as well as gauge field theories in a systematic manner carrying out the Hamiltonian analysis carefully. The decomposition of the fields into positive and negative frequency terms needs to be done carefully after which we show that the (anti) commutation relations for the quantum operators become frame independent. The frame dependence is completely contained in the functions multiplying these operators in the field decomposition. We derive the propagators from the vacuum expectation values of the time ordered products of the fields.

The light-front Hamiltonian and BRST formulations of a two-dimensional Abelian–Higgs model

The Hamiltonian and BRST formulations of an Abelian–Higgs model in one-space one-time dimensions are investigated in the light-front frame under some specific gauge choices. PACS Nos.: 03.65+, 03.70+k, 11.10lm, 11.10Ef, and 11.30Rd

The front-form Hamiltonian and BRST formulations of the Jackiw–Rajaraman chiral Schwinger model

The Hamiltonian and BRST formulations of the Jackiw–Rajaraman chiral Schwinger model are investigated in the light-front frame. PACS No.: 11.15-q

The front-form Hamiltonian and BRST formulations of the Harada-gauged Floreanini–Jackiw action

The Hamiltonian and BRST formulations of the Harada-gauged Floreanini–Jackiw action, which describes a chiral Schwinger model in terms of chiral bosonization, are investigated in the light-front frame. PACS No.: 11.15-q

Gauged Nonlinear Sigma Model in Light-Front Frame: Hamiltonian and BRST Formulations

A gauged nonlinear sigma model in one-space one-time dimension is considered in the light-front frame. The theory is seen to possess a local vector gauge symmetry. The light-front Hamiltonian and BRST formulations of this theory are investigated under some specific light-cone gauges.

Charm and bottom semileptonic decays

We review the present status of theoretical attempts to calculate the semileptonic charm and bottom decays and then present a calculation of these decays in the light-front frame at the kinematic point ${q}^{2}=0$. This allows us to evaluate the form factors at the same value of ${q}^{2}$, even though the allowed kinematic ranges for charm and bottom decays are very different. Also, at this kinematic point the decay is given in terms of only one form factor ${A}_{0}(0)$. For the ratio of the decay rates given by the E653 collaboration we show that the determination of the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements is consistent with that obtained from the unitarity constraint, though a new measurement by the E687 Collaboration is about two standard deviations too high. At present, though, the unitarity method still has greater accuracy. Since comparisons of the semileptonic decays into $\ensuremath{\rho}$ and either electrons or muons will be available soon from the E791 Fermilab experiment, we also look at the massive muon case. We show that for a range of ${q}^{2}$ the SU(3)${}_{F}$ symmetry breaking is small even though the contributions of the various helicity amplitudes becomes more complicated. For $B$ decays, the decay $B\ensuremath{\rightarrow}{K}^{*}l\overline{l}$ at ${q}^{2}=0$ involves an extra form factor coming from the photon contribution and so is not amenable to the same kind of analysis, leaving only the decay $B\ensuremath{\rightarrow}{K}^{*}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ as a possibility. As the mass of the decaying particle increases we note that the SU(3) symmetry becomes badly broken at ${q}^{2}=0$.

Path integral approach to two-dimensional QCD in the light-front frame.

Two-dimensional quantum cromodynamics in the light-front frame is studied following hamiltonian methods. The theory is quantized using the path integral formalism and an effective theory similar to the Nambu-Jona Lasinio model is obtained. Confinement in two dimensions is derived analyzing directly the constraints in the path integral.