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14:00 Zachary Weiner (Illinois U., Urbana)
Title: Seeing the Dark: Gravitational Relics of Dark Photon Production
Abstract: Axion-like particles are a recurrent feature of models of early Universe phenomena, spanning inflation, dark matter, and solutions to the Hubble tension. The nonperturbative decay of axions into beyond the Standard Model photons is a generic feature of these models. I will present the complex nonperturbative and nonlinear dynamics of axion--gauge-field couplings, studied via numerical simulation. These scenarios result in a significant stochastic background of gravitational waves, which provides various means to rule out and constrain models. In the two examples I will present, the (over)production of GHz gravitational waves at preheating imposes the tightest constraints on the inflaton's axial coupling to gauge fields, while early dark energy realized via axion--dark-photon systems are ruled out by CMB constraints at $10^{-16}$ Hz.
14:30 Tom Tong (U. of Oregon)
Title: Custodial Symmetry (Violation) in SMEFT
Abstract: We investigate precision observables sensitive to custodial symmetric/violating UV physics beyond the Standard Model. We use the SMEFT framework which in general includes non-oblique corrections that require a generalization of the Peskin-Takeuchi T parameter to unambiguously detect custodial symmetry/violation. We utilize a new custodial basis which explicitly identifies the global SU(2)_R symmetries of the Higgs and fermion sectors, which in turn permits easy identification of higher-dimensional operators that are custodial preserving or violating. We illustrate our results with several UV theory examples, demonstrating that our generalization faithfully identifies custodial symmetry violation, while the original T can fail.