| Summary: | <p>Three topics in particle phenomenology are independently considered: <em>(1)</em> the flux of prompt atmospheric neutrinos at terrestrial observatories, <em>(2)</em> the resummation of dijet event shapes in Soft-Collinear Effective Theory, and <em>(3)</em> aspects of non-abelian discrete symmetries of flavour. The thesis thus decomposes into three chapters addressing each point in a self-contained way, including short introductions and concluding remarks. Regarding <em>(1)</em>, we calculate the neutrino flux arising from the decay of charmed mesons produced in cosmic ray collisions in the atmosphere, with the charm cross-section being evaluated using NLO QCD techniques and input into a series of equations describing particle cascades. In <em>(2)</em> we present a NNLL' resummation of e<sup>+</sup>e<sup>−</sup> angularities, a class of observables generalizing thrust. This resummation necessarily includes the calculation of two-loop soft anomalous dimensions and matching corrections, which we also detail in generality. Finally, in <em>(3)</em>, we develop a novel ‘bottom-up’ procedure to search for symmetries capable of predicting elements of fermionic mixing matrices and then apply it to both the quark and lepton sectors, finding numerous finite groups of interest.</p>
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