We consider chiral
U(
N) ×
U(
N) models with fermions in the limit of infinitely large local bare Yukawa coupling. When the scalar field is subject to non-linear constraint, phase transitions in ...these models are seen to be identical to those in the corresponding purely bosonic ones. Relaxing the non-linear constraint, we compute the seventh-order strong-coupling series for the susceptibility in these models and analyze them numerically for the
U(2) ×
U(2) case. We find that in four dimensions the approach to the phase transition follows to a good accuracy the mean-field critical behavior, indicating the absence of non-trivial fixed points at strong coupling and being consistent with the first-order nature of the transition. In three dimensions, the strongly-coupled bosonic
U(2) ×
U(2) model (without gauge fields) has a first-order transition strong enough to accommodate electroweak baryogenesis only for a narrow region of the bare parameter space.
The nuclear dependence for 800 GeV/ital c proton production of neutron ital D mesons has been measured near ital xsub ital F=0 in Experiment 789 at Fermilab. ital D mesons from beryllium and gold ...targets were detected with a pair spectrometer and a silicon vertex detector via their decay ital Dr arrowital Kpi. No nuclear dependence is found, with a measured alpha=1.02plus minus0.03plus minus0.02. The measured differential cross section, ital dsigma/ital dxsub ital F, for neutral-ital D-meson production at l angleital xsub ital Fr angle=0.031 is 58plus minus3plus minus7 mub/nucleon. The integrated cross section obtained by extrapolation of the measured cross section to all ital xsub ital F is 17.7plus minus0.9plus minus3.4 mub/nucleon and is consistent with previous measurements.
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