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 $K_{\ell3}$ and $D^0\to K^- \ell^+ \nu_l$ 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 0−0^{-}→\to0−0^{-} Semileptonic Heavy Meson Decays

We present the analysis of exclusive $0^{-}$$\to$$0^{-}$ 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 $^{1}S_{0}(b\bar{b})$ and $^{3}S_{1}(b\bar{s})$ systems as $M_{b\bar{b}}$=9657 MeV and $M_{b\bar{s}}$= 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