The Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model ...Show moreThe Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model (BSM) problems. The BSM problems may be solved by introducing new particles. In addition to particle experiments, cosmological observation offers a way we can put limits on the parameters of these new particles. This work gives a detailed qualitative description of several such cosmological constraints. The observations used are described, and then ways in which new particles could impact such observations. Then, these constraints are applied to two case studies: the scalar portal and the neutrino portal. In both cases, a significant part of the parameter space unexplored by direct experimental studies can be excluded based on these cosmological arguments.Show less
Heavy Neutral Leptons are well-motivated candidates for explaining beyond Standard Model phenomena such as dark matter, baryon asymmetry of the Universe and neutrino oscillations. A variety of...Show moreHeavy Neutral Leptons are well-motivated candidates for explaining beyond Standard Model phenomena such as dark matter, baryon asymmetry of the Universe and neutrino oscillations. A variety of probes, ranging from collider-based to cosmological, explore regions of their parameter space in a complementary way. This work will delve into the possibility that Big Bang Nucleosynthesis has to offer in constraining their lifetime based on cosmological measurements of the Helium-4 abundance. Results are derived for masses up to 100 MeV and a framework is laid for extending the analysis to higher masses.Show less