Scalar Diquarks

In this honours thesis, the effect of adding so-called coloured scalar diquarks to the long-standing Standard Model (SM) is explored. Scalar diquarks are characterised by having the same SM charges as uu, ud, and dd quarks coupled via a Yukawa interaction. A particular interest is placed on scalar diquarks that couple to top quarks, as they're the least experimentally constrained. In this project, the Lagrangians for the eight different types of scalar diquarks were written into FeynRules so that tree-level and loop-level amplitudes could be calculated automatically. The perturbative unitarity bounds of the Yukawa and scalar-scalar coupling parameters were found. Then, the decay widths and cross sections were calculated to investigate the predictions in scattering experiments. Finally, the electroweak precision parameters for the SU(2) singlet scalar diquarks were calculated and found to be ineffective in constraining their possible masses.