393,151 research outputs found
New effective treatment of the light-front nonvalence contribution in timelike exclusive processes
We discuss a necessary nonvalence contribution in timelike exclusive
processes. Following a Schwinger-Dyson type of approach, we relate the
nonvalence contribution to an ordinary light-front wave function that has been
extensively tested in the spacelike exclusive processes. A complicate four-body
energy denominator is exactly cancelled in summing the light-front time-ordered
amplitudes. Applying our method to and
where a rather substantial nonvalence contribution is expected, we find not
only an improvement in comparing with the experimental data but also a
covariance(i.e. frame-independence) of existing light-front constituent quark
model.Comment: 10 pages including 5 figures; Changes: 1-added some sentences;
2-enlarged the figures; 3-added some reference
Light-Front Quark Model Analysis of Exclusive Semileptonic Heavy Meson Decays
We present the analysis of exclusive semileptonic heavy
meson decays using the constituent quark model based on the light-front
quantization. Our model is constrained by the variational principle for the
well-known linear plus Coulomb interaction motivated by QCD. Our method of
analytic continuation to obtain the weak form factors avoids the difficulty
associated with the contribution from the nonvalence quark-antiquark pair
creation. Our numerical results for the heavy-to-heavy and heavy-to-light meson
decays are in a good agreement with the available experimental data and the
lattice QCD results. In addition, our model predicts the two unmeasured mass
spectra of and systems as
=9657 MeV and = 5424 MeV.Comment: 16 pages including 5 figures; version to be published in Phys. Lett.
Towards the MSSM from F-theory
We study the MSSM in F-theory. Its group is the commutant to a structure
group SU(5) x U(1)_Y of a gauge bundle in E_8. The spectrum contains three
generations of quarks and leptons plus vectorlike electroweak and colored
Higgses. The minimal MSSM Yukawa couplings with matter parity is obtained at
the renormalizable level.Comment: 5 pages, 1 figure, published versio
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