Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay

We report on a search for pair production of a fourth generation charge -1/3 quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay via flavor changing neutral currents (FCNC). The search uses the signatures gamma + 3 jets + mu-tag and 2 gamma + 2 jets. We see no significant excess of events over the expected background. We place an upper limit on the production cross section times branching fraction that is well below theoretical expectations for a b' quark decaying exclusively via FCNC for b' quark masses up to m(Z) + m(b).Comment: Eleven pages, two postscript figures, submitted to Physical Review Letter

Two-Loop O(alpha_s G_F M_Q^2) Heavy-Quark Corrections to the Interactions between Higgs and Intermediate Bosons

By means of a low-energy theorem, we analyze at O(alpha_s G_F M_Q^2) the shifts in the Standard-Model W^+W^-H and ZZH couplings induced by virtual high-mass quarks, Q, with M_Q >> M_Z, M_H, which includes the top quark. Invoking the improved Born approximation, we then find the corresponding corrections to various four- and five-point Higgs-boson production and decay processes which involve the W^+W^-H and ZZH vertices with one or both of the gauge bosons being connected to light-fermion currents, respectively. This includes e^+e^- -> f anti-f H via Higgs-strahlung, via W^+W^- fusion (with f = nu_e), and via ZZ fusion (with f = e), as well as H -> 2V -> 4f (with V = W, Z).Comment: 20 pages (Latex); Physical Review D (to appear

A Cytokinin Analog Thidiazuron Suppresses Shoot Growth in Potted Rose Plants via the Gibberellic Acid Pathway.

Application of thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5-ylurea, TDZ), a cytokinin analog, to inhibit the leaf yellowing that occurs after pinching potted rose plants, resulted in compact plants with shorter shoots and thicker internodes. Two weeks after treatment with 100 μM of TDZ, new shoots were half as long as those in control plants, and stem diameters were about 40% greater. This effect of TDZ is associated with changes in cell architecture. Although TDZ treatment stimulated ethylene production by the plants, inhibitors of ethylene biosynthesis (2-aminoethoxyvinyl glycine) or action (silver thiosulfate) did not affect the response of plants to TDZ. We found that TDZ treatment significantly suppressed the expression of bioactive gibberellic acid (GA) biosynthesis genes encoding GA3 and GA20 oxidases and slightly increased the expression of GA catabolism genes encoding GA2 oxidase. Application of GA3 and TDZ together resulted in normal elongation growth, although stem diameters were still somewhat thicker. Our results suggest that TDZ regulates shoot elongation and stem enlargement in potted rose plants through the modulation of bioactive GA biosynthesis