We implement a dispersive parameterization of the nonlocal form factors (NFFs) governing photon or $Z$-boson exchange in the semileptonic $K^+ \to \pi^+ \ell^+ \ell^-$ $(\ell=e,\mu)$ and $K^+ \to \pi^+ \nu \bar{\nu}$ decays, respectively, to improve the theoretical description of the spectrum and decay rate of the golden neutrino mode. The parameterization links the hadronic $K^+ \pi^- \to...
We present a Lattice QCD calculation of the radiative decay rates of the kaon $K^- \to \ell^- \bar{\nu}_{\ell} \gamma^{(*)}$, with a real or virtual photon, and $\ell = e, \mu$. The simulations are performed with physical kaon and pion masses, using gauge ensembles generated by the Extended Twisted Mass Collaboration with $N_f = 2+1+1$ flavors of Wilson-Clover twisted mass fermions.
For...
The NA62 experiment at CERN reports preliminary results from the study of the rare radiative decay $K^+ \rightarrow \pi^+ \pi^+ \pi^- \gamma$, using a data sample collected with a multi-track trigger in 2017-2018. A measurement of the branching ratio as a function of the photon energy in the kaon rest frame is presented and compared with previous measurements and theoretical predictions.
Precise tests of CKM unitarity provide a probe of physics beyond the Standard Model. Using the most precise determinations—$V_{ud}$ from superallowed nuclear $\beta$ decays and $V_{us}$ from kaon leptonic and semileptonic decays—the first‑row sum $|V_{ud}|^{2}+|V_{us}|^{2}+|V_{ub}|^{2}$ deviates from unitarity by $2\text{–}3\,\sigma$. This tension emphasizes the need for further reductions in...
In my talk I will present an overview of Kaon observables analyzed within the Standard Model Effective Field Theory (SMEFT) framework. Focusing on Kaon mixing, rare decays, and direct CP violation, I will discuss how these processes constrain higher-dimensional SMEFT operators. The treatment includes renormalization group evolution, matching to the low-energy effective theory, and the role of...
