High Energy Physics Seminar

Abstract: The redundancy introduced by field redefinitions poses a challenge in the Lagrangian formulation of effective field theories (EFTs), often obscuring the underlying physical content. The analogy between field redefinitions and coordinate transformations suggests that EFTs may admit a geometric reformulation that makes their physics more transparent. While non-derivative field redefinitions can be naturally accommodated within the field space geometry on the target manifold, this formalism breaks down once derivatives enter the transformations. In this talk, I will present an extension of the geometric framework—known as functional geometry—that incorporates derivative field redefinitions, and I will discuss its relation to the field space geometry, focusing on scattering amplitudes. This geometric perspective offers new insights into the structure of EFT amplitudes and paves the way toward a formulation of EFTs free from the redundancies of field redefinitions.

Abstract: New physics beyond the standard model is highly anticipated, especially by dark matter and the recently discovered Higgs boson considerations. With the successful exploration and new knowledge from various particle physics experiments, weakly-coupled new physics through various portals bear great potential for discovery but also pose significant challenges. In this colloquium, I present a general consideration of possible complex dark sector structure, which couples to the SM through feebly coupled messenger fields. These messenger field considerations define new goals for particle physics and motivate new ideas in searching for them from large-scale experiments to small-scale experiments. The searches for hidden sector dynamics grow rapidly and spread across different frontiers of particle physics. I will present several exciting new ideas and discuss the future perspectives in this active research area of dark sector messenger hunting.

Abstract: Understanding strongly coupled gauge theories is a long-standing challenge in particle physics. Quantum Chromodynamics (QCD), with its phenomena of confinement and chiral symmetry breaking, remains particularly elusive. To gain new insight, a systematic approach , has been developed based on supersymmetric SU($N$) gauge theories deformed by anomaly-mediated supersymmetry breaking (AMSB). In this talk, I will discuss several recent results, including the emergence of a branch-like $\eta'$ potential and the intricate CP structure of QCD-like theories at $\theta = \pi$. Strikingly, many of these features mirror those of ordinary QCD, providing fresh theoretical tools to probe its nonperturbative regime. I will also highlight the possibility that the up quark mass is generated entirely through nonperturbative dynamics as an elegant solution to the strong CP problem. Remarkably, for three colors and three flavors ($N = F = 3$), the dynamically generated up-quark mass can lead to a dynamical up quark mass that is large enough to account for its entire physical mass.

Abstract: Primordial Black Holes (PBHs) are fascinating cosmological objects for a number of reasons: they are one of the most compelling candidates to explain some or all of the missing matter (dark matter) in our universe; they are one of only a couple potential probes of the first few seconds of the universe’s infancy, and they may also one day furnish an observational probe of quantum gravity through detection of Hawking radiation. As such, it is crucial to understand the mechanisms by which PBHs form. In this talk, I go beyond the already-described single-field inflationary models that typically produce PBHs through a period of ultra-slow-roll (USR), which are usually highly fine-tuned. I will first discuss the formation of PBHs in the context of two natural high-energy ingredients: multiple scalar fields and non-minimal gravitational couplings. I will reveal what we have learned by performing the first Markov Chain Monte Carlo (MCMC) analysis of parameter space for such models, and how these models can produce all of the dark matter while also satisfying the most recent Planck constraints, and even have natural UV completions in, for example, supergravity (SUGRA). I’ll then present a new generic mechanism in which a single-field inflationary model with an additional scalar spectator generates large power spectrum enhancements while still reducing the severity of the fine-tuning of single-field models (sans spectator) by orders of magnitude. In this mechanism, the system undergoes two turns in field space bracketing a phase where tachyonic isocurvature modes grow exponentially before transferring power to curvature perturbations. Crucially, this occurs without entering a USR phase. I will explicitly demonstrate the remarkable resilience of this inflationary mechanism to parameter variations. If time permits, I will discuss the specific case in which the spectator field is the axion. 

Abstract: Ever since the discovery of neutrino masses from the phenomenon of neutrino oscillations, the race to understand neutrino properties has evolved dramatically. Within the context of the Standard Model (SM) of particle physics, neutrinos are massless -- the observation of oscillations requires physics beyond the SM (BSM). In this talk, I will highlight the many ways in which present-day (and near-future) neutrino experiments are searching for BSM physics. This includes a suite of experiments -- SBN -- currently collecting data at Fermilab, and the planned long-baseline neutrino experiment DUNE, sending neutrinos from Fermilab to South Dakota. With preparation, a number of discoveries -- from explanations of neutrino masses to disconnected models regarding dark matter -- could await!

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