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The Standard Model (SM) of particle physics has proven to
be the most successful theory in describing elementary particles and
their interactions. However, it still faces significant challenges,
from issues like the fine-tuning problem, the baryon asymmetry of the
universe (BAU), the existence of neutrino mass, and dark matter etc.
Numerous ultraviolet (UV) complete theoretical models, such as
supersymmetry and composite Higgs, have been proposed to address these
issues. In this thesis, we adopt a bottom-up approach to explore
beyond Standard Model (BSM) physics, with electroweak precision
measurements serving as one of our key guiding principles. The
$\rho$-parameter imposes a strong constraint on the non-doublet vacuum
expectation value (VEV), suggesting that models with doublets are
strongly favored by nature. However, are the scenarios with SU(2)
doublet scalars, the only viable options? In this work, we focus on a
triplet scenario, specifically the Georgi-Machacek model, which allows
for a large triplet VEV while still respecting the $\rho$-parameter.
We will first derive the constraints on the parameter space of this
scenario and then investigate its phenomenological implications, both
in collider experiments and cosmological contexts.
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