10010334 - Probing the Origin of Flavor with Colliders and Gravitational Waves

The origin of the observed pattern of fermion masses, mixings, and CP violation remains one of the central unresolved problems of particle physics. At the same time, the remarkable suppression of flavor-changing processes places extremely strong constraints on new physics at the TeV scale. Understanding how new physics can respect these constraints while still producing observable signals is therefore a major challenge. This project addresses the flavor puzzle through a research program that combines effective field theory, collider and flavor phenomenology, model building, and early-universe cosmology.

The project is organized into two closely connected parts. Part I develops Minimal Flavor Protection (MFP) into a sufficiently general yet predictive framework for the interpretation of flavor and collider data beyond Minimal Flavor Violation (MFV). MFV has long served as the standard paradigm for flavor-safe new physics, but it is highly restrictive and may not capture the broader range of possibilities accessible to present and future experiments. MFP instead identifies the minimal approximate flavor symmetry required to protect TeV-scale new physics from existing constraints. This opens a new parameter space in which sizable violations of flavor universality and symmetry-allowed flavor-charged currents can arise while remaining consistent with present data. The main objectives are to classify the space of MFP-like symmetry–spurion structures, determine the experimentally viable region of maximal universality violation, identify which flavor-charged currents can arise at leading order, and apply the MFP framework to representative classes of new-physics models.

Part II investigates the cosmological dynamics of flavor symmetry breaking and the resulting stochastic gravitational-wave backgrounds (SGWB). Flavor models often involve scalar sectors whose symmetry-breaking dynamics can trigger strong first-order phase transitions in the early universe. Such transitions may generate gravitational-wave signals potentially observable by future detectors. This project will determine which classes of flavor models can produce observable signals, characterize the predicted gravitational-wave spectra for both TeV-scale and high-scale flavor dynamics, and explore the complementarity between gravitational-wave observations and laboratory probes of flavor physics.

The proposed research advances the state of the art in two ways. First, it develops MFP from a recently proposed concept into a systematic framework for BSM flavor interpretation, extending and complementing existing symmetry-based approaches such as MFV. Second, it explores a largely unexplored connection between flavor physics and gravitational-wave astronomy by establishing a program to study SGWB signals from flavor model building.

The research approach combines symmetry-based analyses, effective field theory, perturbative quantum field theory, collider and flavor phenomenology, finite-temperature field theory, and gravitational-wave predictions. The project will be carried out by the PI together with one postdoctoral researcher and one doctoral student. The postdoctoral researcher will focus on formal developments and precision phenomenology, while the doctoral student will work on benchmark implementations, numerical analyses, and sensitivity forecasts. Together, the two parts of the project aim to advance a unified perspective in which approximate flavor symmetries guide both the search for new physics in laboratory experiments and the exploration of the dynamical origin of flavor in the early universe.