QCD in the Standard Model and Beyond

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This grant proposal involves work aimed at elucidating the dynamics of the Standard Model (SM) of particle physics, both in the context of the SM itself, and in the context of determinations of SM contributions to processes currently under investigation as part of a world-wide effort, involving intensive ongoing experimental programs at major experimental facilities in Russia, Switzerland, Italy, the US, Japan and China, to search for signals of physics beyond the Standard Model. In these processes, a precision understanding of SM contributions is crucial to the success of these very expensive experimental programs since SM contributions serve as backgrounds which must be thoroughly and precisely understood if beyond-the-SM effects are to be unambiguously identified. Of particular importance in this regard is the determination of the effects of the strong interactions, which, due to their strength (1) can be very numerically significant and (2) are amenable to treatment using a much more limited set of theoretical techniques than are effects produced by the weaker electromagnetic and weak interactions. Strong interaction effects will be evaluated using Quantum Chromodynamics (QCD), the theory of the strong (nuclear and sub-nuclear) interactions, employing a number of rigorous, well-established theoretical techniques, including large scale numerical simulations (lattice QCD), QCD sum rules (a class of relations based on general mathematical constraints), and effective low-energy theories. I and my research collaborators will use these techniques, in combination with experimental data from various collider facilities, to make state-of-the-art determinations of SM parameters such as the strength of the strong interaction coupling and the up-strange Cabibbo-Kobayashi-Maskawa matrix element, a parameter which describes how rapidly a hadronic state containing a strange quark can decay into states where the strange quark has been converted into an up quark. An improved determination of this latter quantity based on the strange hadronic decays of the heavy tau lepton is of particular interest in view of current hints that the weak interactions might couple with different strengths to the electron, muon and tau lepton, a possibility that would provide unambiguous evidence for the presence of physics beyond the SM. I and other collaborators, will also continue previous theoretical work on possible not-yet-detected novel ("exotic") states of hadronic matter. Part of the work in in this proposal will also involve creating a suite of computer programs which will allow experimentalists to perform theoretical, QCD-based analyses of the new experimental data on hadronic decays of the tau lepton to be generated as part of the multi-year program which commenced recently at the Belle II facility in Japan. The work in this grant proposal will thus also serve to increase the effectiveness of the collaboration between particle theorists and experimentalists.