68 research outputs found
Q^2-Dependence of the Drell-Hearn-Gerasimov integral
The energy and four-momentum (Q^2) dependence of the photo-absorption cross
section on the proton is calculated for helicity -1/2 and -3/2 states. An
effective Lagrangian model is used, formulated in terms of meson and baryon
degrees of freedom, which obeys crossing symmetry, unitarity, Lorentz and gauge
invariance. The difference in the cross sections for the two helicity states,
the Drell-Hearn-Gerasimov integral , is evaluated at different
. We find that at small momentum transfer the absolute value of
first increases to reach a maximum at
before decreasing at higher .Comment: 8 pages, 3 figures, revte
Angular distribution and forward-backward asymmetry of the Higgs-boson decay to photon and lepton pair
The Higgs-boson decay h -> gamma l+ l- for various lepton states l = (e, mu,
tau) is analyzed. The differential decay width and forward-backward asymmetry
are calculated as functions of the dilepton invariant mass in a model where the
Higgs boson interacts with leptons and quarks via a mixture of scalar and
pseudoscalar couplings. These couplings are partly constrained from data on the
decays to leptons, h -> l+ l-, and quarks h -> q \bar{q} (where q = (c, b)),
while the Higgs couplings to the top quark are chosen from the two-photon and
two-gluon decay rates. Nonzero values of the forward-backward asymmetry will
manifest effects of new physics in the Higgs sector. The decay width and
asymmetry integrated over the dilepton invariant mass are also presented.Comment: 9 pages, 4 figures, SVJour3 class; v2: minor changes in text,
references updated and extended, corresponds to journal versio
Electromagnetic interaction in chiral quantum hadrodynamics and decay of vector and axial-vector mesons
The chiral invariant QHD-III model of Serot and Walecka is applied in the calculation of some meson properties. The electromagnetic interaction is included by extending the symmetry of the model to the local U(1) \times SU(2)_{R} \times SU(2)_{L} group. The minimal and nonminimal contributions to the electromagnetic Lagrangian are obtained in a new representation of QHD-III. Strong decays of the axial-vector meson, a_{1} \to \pi \rho, a_{1} \to \pi \sigma, and the electromagnetic decays \rho \to \pi \pi \gamma, a_{1} \to \pi \gamma and \rho \to \pi \gamma are calculated. The low-energy parameters for the \pi-\pi scattering are calculated in the tree-level approximation. The effect of the auxiliary Higgs bosons, introduced in QHD-III in order to generate masses of the vector and axial-vector mesons via the Higgs mechanism, is studied as well. This is done on the tree level for \pi-\pi scattering and on the level of one-loop diagrams for the a_{1} \to \pi \gamma decay. It is demonstrated that the model successfully describes some features of meson phenomenology in the non-strange sector
Lepton-pair production in virtual Compton scattering off the proton
We show that lepton-pair production in Virtual Compton Scattering offers,
through interference with the well-known Bethe-Heitler process, a sensitive
probe to learn the longitudinal response of resonances and the electromagnetic
nucleon form factors. This interference can be measured directly in terms of an
asymmetry. The role of off-shell effects in the N-N- vertices is
investigated as well. An additional N-N- contact term in the
amplitude, included to ensure gauge invariance of the model, cancels a
substantial part of the off-shell effects.Comment: 8 pages, LaTeX , 2 figures. To appear in Phys. Lett.
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