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Register a new userEletroweak Form Factors in the Light-Front for Spin-1 Particles
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Joao Pacheco B. C. de Melo Dr.
Publication date
2012
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English
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The contribution of the light-front valence wave function to the electromagnetic current of spin-1 composite particles is not enough to warranty the proper transformation of the current under rotations. The naive derivation of the plus component of the current in the Drell-Yan-West frame within an analytical and covariant model of the vertex leads to the violation of the rotational symmetry. Computing the form-factors in a quasi Drell-Yan-West frame $q^+rightarrow 0$, we were able to separate out in an analytical form the contributions from Z-diagrams or zero modes using the instant-form cartesian polarization basis.
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J. P. B. C. de Melo
, Anace N. da Silva (Laboratorio de Fisican Teorica e Computacional
, LFTC
2015
For the vector sector, i.e, mesons with spin-1, the electromagnetic form factors and anothers observables are calculated with the light-front approach. However, the light-front quantum field theory have some problems, for example, the rotational symmetry breaking. We solve that problem added the zero modes contribuition to the matrix elements of the electromagnetic current, besides the valence contribuition. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the $0to 0$ one carries zero mode contributions.
We predict the $mathcal{V} to mathcal{P} gamma$ decay widths and the $mathcal{V} to mathcal{P} gamma^{*}$ transition form factors, where $mathcal{V}=(rho, omega, K^*, phi)$ and $mathcal{P}= (pi,K, eta,eta^prime)$, using spin-improved holographic light-front wavefunctions for the mesons. We find excellent agreement with the available data for both the decay widths and the timelike transition form factors extracted from the leptonic conversion decays $mathcal{V} to mathcal{P} l^+ l^-$.
We investigate the electromagnetic form factors of the nucleon in the framework of basis light front quantization. We compute the form factors using the light front wavefunctions obtained by diagonalizing the effective Hamiltonian consisting of the holographic QCD confinement potential, the longitudinal confinement, and a one-gluon exchange interaction with fixed coupling. The electromagnetic radii of the nucleon are also computed.
We construct spin-improved holographic light-front wavefunctions for the nucleons (viewed as quark-diquark systems) and use them to successfully predict their electromagnetic Sachs form factors, their electromagnetic charge radii, as well as the axial form factor, charge and radius of the proton. The confinement scale is the universal mass scale of light-front holography, previously extracted from spectroscopic data for light hadrons. With the Dirac and Pauli form factors normalized using the quark counting rules and the measured anomalous magnetic moments respectively, the masses of the quark and diquark are the only remaining adjustable parameters. We fix them using the data set for the protons Dirac-to-Pauli form factor ratio, and then predict all other data without any further adjustments of parameters. Agreement with data at low momentum-transfer is excellent. Our findings support the idea that light (pseudoscalar and vector) mesons and the nucleons share a non-perturbative universal holographic light-front wavefunction which is modified differently by their spin structures.
In an explicitly covariant light-front formalism, we analyze transition form factors between pseudoscalar and scalar mesons. Application is performed in case of the $B to f_0(980)$ transition in the full available transfer momentum range $q^2$.
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