Speaker
Description
In this talk I will present a universal second-order $U$-spin master rate sum rule among the CKM-free Cabibbo-favored (CF), doubly Cabibbo-suppressed (DCS), and singly Cabibbo-suppressed (SCS) decay rates of weak charm decays in the Standard Model,
\begin{equation}
\frac{\text{sum of CF and DCS CKM-free rates}}{\text{sum of SCS CKM-free rates}} = 1\,,
\end{equation}
which holds up to second order in $U$-spin breaking. I will sketch the general group-theoretic construction underlying this relation and emphasize that, while the phenomenological application here is to charm decays, the construction itself is far more general. I will discuss the current status of this sum rule in charm systems. If time permits, I will also comment on possible extensions beyond charm and on broader directions toward understanding and applying higher-order flavor sum rules.