PhD Theses (Physics)

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Browsing PhD Theses (Physics) by Subject "Beyond the Standard Model"

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    Implications of Flavour Data on Dark Matter Phenomenology
    (2022) Mukherjee, Lopamudra
    The Standard Model of particle physics, with all its elegance, has survived most experimental tests at particle accelerators, but not all. This thesis arises in the context of dark matter phenomenology, whose ubiquitous existence cannot be explained within the Standard Model framework. The nature and particle content of dark matter is still a mystery, and proposing suitable models that can explain its properties would be of great value. In this thesis, we perform systematic studies of the phenomenology of dark matter models, focusing on the rich consequences the lepton and quark flavour physics can have for the dark sector. In this regard, we highlight the important observables that play a crucial role in identifying and quantifying possible newphysics along with their present experimental status. This sets the essential background of the studies included in the thesis. We then move on to investigate two popular new physics models, the Inert Higgs Doublet model and the U(1)X extension of SM, that not only gives rise to a suitable DM candidate, but are also motivated by other general issues of the SM, such as light neutrino masses and lepton flavour violation etc. We quantify the contributions from new degrees of freedom to various flavour physics observables such as branching fractions of meson decays, meson-mixings etc. We have displayed the outcome of precise flavour data on the dark matter parameter space while simultaneously explaining some anomalous results in low energy observables. We also highlight some interesting features of these models that allow us to probe our model parameters both in DM and high energy collider experiments using simple cut-based analysis. Further, we have shown how the mediators in WIMP-nucleon scattering can modify elementary quark vertices with the W-boson, which impacts the extraction of the CKM elements. Using the most up-to-date measurements, we successfully constrain the masses and couplings of mediators having scalar or pseudoscalar interactions with the dark matter and SM quarks. In summary, this thesis provides a comprehensive outlook towards the implications of flavour phenomenology on new physics models, with a particular focus on the dark sector.
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    Search for New Physics at the future Lepton Coliders
    (2024) Jahedi, Sahabub
    The Standard Model (SM) of particle physics has successfully explained the fundamental forces of nature and was solidified with the discovery of the Higgs boson. However, various theoretical and experimental motivations drive us to explore beyond the SM (BSM). Statistical analysis plays a crucial role in this exploration, applied to different collider experiments to search for different BSM scenarios. Chapter 1 of the thesis introduces the SM particle spectrum, its limitations, and discusses approaches to address these limitations. It also outlines the outlook for past, present, and future colliders, focusing on lepton colliders. Chapter 2 delves into two statistical techniques: binned analysis and the optimal observable technique (OOT). Chapter 3 explores OOT in a BSM-dominated scenario, particularly in estimating Z boson couplings at e+e- collider and studying dark matter phenomenology. Chapter 4 shifts focus to scenarios where the SM dominates, investigating the determination of anomalous neutral triple gauge couplings (nTGCs) through diboson production and dimension-6 effective couplings through top-quark pair production at the e+e- collider. Chapter 5 examines experimental constraints on dimension-6 four-Fermi SMEFT operators and explores flavor probes through flavor-changing top-charm production at the muon collider. Chapter 6 studies optimal sensitivity of NP couplings in the presence of SM background using numerical techniques. Finally, Chapter 7 provides a summary of the thesis and suggests potential future directions