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Abstract
The realization that first- and second-generation Yukawa couplings can be probed by decays of the Higgs boson to a meson in association with a photon has renewed interest in such rare exclusive decays. We present here a detailed study of the rare Z-boson processes Z → J/ψ + γ, Z → ϒ + γ, and Z → &phis; + γ that can serve as benchmarks for the analogous Higgs-boson decays. Also, we present a study of Higgs rare decays, h → &phis; + γ, h → ρ + γ, and h → ω + γ. We include both direct-production and fragmentation contributions to these decays, and consider the leading QCD corrections and the relativistic corrections by using different tools. Among all the tools, we heavily use NRQCD(Non-relativistic QCD) and LCDA(Light-Cone Distribution Amplitudes). In this thesis we will present an introduction to both NRQCD and LCDA. Finally, we present our numerical predictions for the branching ratios that include a careful accounting of the theoretical uncertainties.
