arXiv subjects

Cédric Lorcé

Publications and source records attributed to Cédric Lorcé.

78 records · Page 5Linked to original sources

arXiv2009

Electromagnetic Properties for Arbitrary Spin Particles: Part 1 $-$ Electromagnetic Current and Multipole Decomposition

In a set of two papers, we propose to study an old-standing problem, namely the electromagnetic interaction for particles of arbitrary spin. Based on the assumption that light-cone helicity at tree level and $Q^2=0$ should be conserved non-trivially by the electromagnetic interaction, we are able to derive \emph{all} the natural electromagnetic moments for a pointlike particle of \emph{any} spin. In this first paper, we propose a transparent decomposition of the electromagnetic current in terms of covariant vertex functions. We also define in a general way the electromagnetic multipole form factors, and show their relation with the electromagnetic moments. Finally, by considering the Breit frame, we relate the covariant vertex functions to multipole form factors.

hep-ph↗

arXiv2009

Electromagnetic Properties for Arbitrary Spin Particles: Part 2 $-$ Natural Moments and Transverse Charge Densities

In a set of two papers, we propose to study an old-standing problem, namely the electromagnetic interaction for particles of arbitrary spin. Based on the assumption that light-cone helicity at tree level and $Q^2=0$ should be conserved non-trivially by the electromagnetic interaction, we are able to derive \emph{all} the natural electromagnetic moments for a pointlike particle of \emph{any} spin. In this second paper, we give explicit expressions for the light-cone helicity amplitudes in terms of covariant vertex functions, leading to the natural electromagnetic moments at $Q^2=0$. As an application of our results, we generalize the discussion of quark transverse charge densities to particles with arbitrary spin.

hep-ph↗

arXiv2009

Quark transverse charge densities in the $Δ(1232)$ 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 $G_{E2}(0$) 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.

hep-ph↗

arXiv2008

Baryon vector and axial content up to the 7Q component

We have used the light-cone formulation of Chiral-Quark Soliton Model to investigate the vector and axial content of octet, decuplet and the hypothetical antidecuplet in the flavor SU(3) symmetry limit. We have extended previous works by computing the 7Q contribution to vector and axial charges for the octet and antidecuplet but stayed at the 5Q sector for the decuplet where the full computation needs much more time. As expected the 7Q component has a weaker impact on the quantities but still changes them by a few percent. We give also a detailed decomposition of those charges into flavor, valence quark, sea quark and antiquark contributions. Many of them are of course not (yet) measured or estimated and constitute then a theoretical estimation. Among the different interesting observations made in this work are the explicit quadrupole deformation of decuplet baryons due to the pion field and the sum of quark spins larger than the pentaquark one.

hep-ph↗

arXiv2007

Tensor charges of light baryons in the Infinite Momentum Frame

We have used the Chiral-Quark Soliton Model formulated in the Infinite Momentum Frame to investigate the octet, decuplet and antidecuplet tensor charges up to the 5Q level. Using flavor SU(3) symmetry we have obtained for the proton $δu=1.172$ and $δd=-0.315$ in fair agreement previous model estimations. The 5Q allowed us to estimate also the strange contribution to the proton tensor charge $δs=-0.011$. All those values have been obtained at the model scale Q^2=0.36 GeV^2.

hep-ph↗

arXiv2006

Improvement of the Theta+ width estimation method on the Light Cone

Recently, Diakonov and Petrov have suggested a formalism in the Relativistic Mean Field Approximation allowing one to derive the 3-, 5-, 7-,... quark wavefunctions for the octet, decuplet and antidecuplet. They have used this formalism and many strong approximations in order to estimate the exotic Theta+ width. The latter has been estimated to ~4 MeV. Besides they obtained that the 5-quark component of the nucleon is about 50% of its 3-quark component meaning that relativistic effects are not small. We have improved the technique by taking into account some relativistic corrections and considering the previously neglected 5-quark exchange diagrams. We also have computed all nucleon axial charges. It turns out that exchange diagrams affect very little Diakonov's and Petrov's results while relativistic corrections reduce the Theta+ width to ~2 MeV and the 5- to 3-quark component of the nucleon ratio to 30%.

hep-ph↗