New physics searches at kaon and hyperon factories.

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

Searching for ultra-light bosons and constraining black hole spin distributions with stellar tidal disruption events.

Stars that pass close to the supermassive black holes located in the center of galaxies can be disrupted by tidal forces, leading to flares that are observed as bright transient events in sky surveys. The rate for these events to occur depends on the black hole spins, which in turn can be affected by ultra-light bosons due to superradiance. We perform a detailed analysis of these effects and show that searches for stellar tidal disruptions have the potential to uncover the existence of ultra-light bosons. In particular, we find that upcoming stellar tidal disruption rate measurements by the Vera Rubin Observatory's Legacy Survey of Space and Time can be used to either discover or rule out bosons with masses ranging from 10-20 to 10-18 eV. Our analysis also indicates that these measurements may be used to constrain a variety of supermassive black hole spin distributions and determine if close-to maximal spins are preferred.

Light Scalars and the Koto Anomaly.

We show that the recent excess presented by KOTO in their search for K_{L}→π^{0}νν[over ¯] may be due to weakly coupled scalars produced from Kaon decays. We study two concrete realizations, the minimal Higgs portal and a hadrophilic scalar model, and demonstrate that they can explain the observed events while satisfying existing limits. The simplicity of these models, and their possible relations to interesting UV constructions, provides strong theoretical motivation for a new physics interpretation of the KOTO data.

Aligned and Spontaneous Flavor Violation.

We present a systematic spurion setup called aligned flavor violation (AFV) that allows for new physics couplings to quarks that are aligned with standard model (SM) Yukawa couplings, but do not necessarily share their hierarchies nor are family universal. Additionally, we show that there is an important subset of AFV called spontaneous flavor violation (SFV), which naturally arises from UV completions where the quark family number and CP groups are spontaneously broken. Flavor-changing neutral currents are strongly suppressed in SFV extensions of the SM. We study SFV from an effective field theory perspective and demonstrate that SFV new physics with significant and preferential couplings to first or second generation quarks may be close to the TeV scale.