1,990 research outputs found
Spin-1 Particle in the Light-Front Approach
The electromagnetic current of spin-1 composite particles does not transform
properly under rotations if only the valence contribution is considered in the
light-front model. In particular, the plus component of the current, evaluated
only for the valence component of the wave function, in the Drell-Yan frame
violates rotational symmetry, which does not allow a unique calculation of the
electromagnetic form-factors. The prescription suggested by Grach and
Kondratyuk [Sov. J. Nucl. Phys. 38, 198 (1984)] to extract the form factors
from the plus component of the current, eliminates contributions from pair
diagrams or zero modes, which if not evaluated properly cause the violation of
the rotational symmetry. We address this problem in an analytical and covariant
model of a spin-1 composite particle.Comment: To appear Brazilian Journal of Physics (2004), 4 pages, no figures.
Use multicols.st
Light-Front projection of spin-1 electromagnetic current and zero-modes
The issue of the contribution of zero-modes to the light-front projection of
the electromagnetic current of phenomenological models of vector particles
vertices is addressed in the Drell-Yan frame. Our analytical model of the
Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives
a physically motivated light-front wave function symmetric by the exchange of
the fermion and antifermion, as in the -meson case. We found that among
the four independent matrix elements of the plus component in the light-front
helicity basis only the one carries zero mode contributions. Our
derivation generalizes to symmetric models, important for applications, the
above conclusion found for a simplified non-symmetrical form of the spin-1
Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a
smeared fermion-photon vertex model.Comment: Use elservier style. 14 page
Renormalization of an effective Light-Cone QCD-inspired theory for the Pion and other Mesons
The renormalization of the effective QCD-Hamiltonian theory for the
quark-antiquark channel is performed in terms of a renormalized or fixed-point
Hamiltonian that leads to subtracted dynamical equations. The fixed
point-Hamiltonian brings the renormalization conditions as well as the
counterterms that render the theory finite. The approach is renormalization
group invariant. The parameters of the renormalized effective QCD-Hamiltonian
comes from the pion mass and radius, for a given constituent quark mass. The 1s
and excited 2s states of are calculated as a function of the mass of
the quark being s, c or b, and compared to the experimental values.Comment: 39 pages, 10 figure
Application of the equipartition theorem to the thermal excitation of quartz tuning forks
The deflection signal of a thermally excited force sensor of an atomic force
microscope can be analyzed to gain important information about the detector
noise and about the validity of the equipartion theorem of thermodynamics.
Here, we measured the temperature dependence of the thermal amplitude of a
tuning fork and compared it to the expected values based on the equipartition
theorem. In doing so, we prove the validity of these assumptions in the
temperature range from 140K to 300K. Furthermore, the application of the
equipartition theorem to quartz tuning forks at liquid helium temperatures is
discussed.Comment: 8 pages, 3 figures, published in Applied Physics Letter
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