Related papers: Exploring scalar contributions with $K^+ \to \pi^+…
We analyze the rare kaon decays $K_L \to \pi^0 \nu \bar \nu$, $K^+ \to \pi^+ \nu \bar \nu$, $K_L \to \pi^0 e^+ e^-$ and $K_L \to \mu^+ \mu^-$ in conjunction with the CP violating ratio $\epsilon'/\epsilon$ in a general class of…
The ratio $R_K = \Gamma(K^{\pm}\to e^{\pm}\nu(\gamma)) / \Gamma(K^{\pm}\to\mu^{\pm}\nu(\gamma))$ provides a powerful probe of the structure of weak interactions. It is calculated with very high precision within the Standard Model, but…
Recent reports of the observation of the decay $\tau \rarrow \nu_{\tau} + K + \pi + \pi$ raise interesting questions. The $u-s$ quark mass difference can induce an effective second-class current in the strange sector and enhance decays to…
The first search for ultra-rare $K^+$ decays into the $\pi^+e^+e^-e^+e^-$ final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017-2018. An upper limit of $1.4\times 10^{-8}$ at 90% CL is obtained for the…
Rare kaon decays provide unique opportunity to test the Standard Model and probe its possible extensions. The final result on the lepton universality test by measuring the ratio R_K = G(K+- to e+- nu)/G(K+- to mu+- nu) is presented as well…
The decay $K^+ \to \pi^+ \nu \bar{\nu}$, with a very precisely predicted branching ratio of less than $10^{-10}$, is one of the best candidates to reveal indirect effects of new physics at the highest mass scales. The NA62 experiment at the…
We study the rare decay $B\to K_2^\ast(1430)(\to K\pi)\ell^+\ell^-$ in the Standard Model and beyond. Working in the transversity basis, we exploit the relations between the heavy-to-light form factors in the limit of heavy quark ($m_b\to…
The rare decays of a kaon into a pion and a charged lepton/antilepton pair proceed via a flavour changing neutral current and therefore may only be induced beyond tree level in the Standard Model. This natural suppression makes these decays…
We briefly review the status of rare radiative and semileptonic $b \to s (\gamma, \ell^+ \ell^-)$, ($\ell=e,\mu$) decays. We discuss possible signatures of new physics in these modes and emphazise the role of the exclusive channels. In…
We present the first complete lattice QCD calculation of the four structure-dependent form factors governing the rare charged kaon decay $K^- \to \ell^- \bar{\nu}_\ell \ell'^+ \ell'^-$, with fully controlled statistical and systematic…
The CERN NA62 experiment uses a novel "kaon decay-in-flight" technique to observe $K^+ \to \pi^+ \nu \overline{\nu}$. The preliminary result based on the analysis of the full 2016 dataset will be presented. In agreement with the Standard…
We use three-point QCD sum rules to calculate the form factors governing the rare exclusive decays B \to (K,K^*) \ell^+ \ell^-, B \to (K,K^*) \nu \bar\nu. We predict the branching ratios, the invariant mass distributions of the lepton pair…
We study impacts on new physics search from the rare decay $K^+ \to \pi^+ \nu \bar{\nu}$. In a certain class of new physics models, the extra contributions to FCNC processes can be parametrized by its ratio to the standard model (SM)…
The exclusive (B -> K_2 l^+ l^-) decay is studied using the most general, model independent four-fermion interaction. The sensitivity of the ratio of the decay widths when K_2 meson is longitudinally and transversally polarized, the…
We define and test $\mathrm{CP}$-even and $\mathrm{CP}$-odd partial differential widths for the process $\tau\rightarrow K\pi\pi\nu_{\tau}$ assuming that an intermediate heavy charged scalar contributes to the decay amplitude. Adopting a…
Motivated by the LHCb measurement of the hyperon decay mode $\Sigma^+\to p\mu^+\mu^-$ and prospects for improvement, we revisit the estimates for the rate and muon forward-backward asymmetry within the standard model and beyond. The…
In this letter we revisit the Standard Model predictions for $\mathcal{B}(B\to K^{(\ast)}\nu\bar{\nu})$ and discuss the opportunities that open up when combining its partial decay rate with that of $B\to K^{(\ast)}\ell\ell$. In the Standard…
We report a first, complete lattice QCD calculation of the long-distance contribution to the $K^+\to\pi^+\nu\bar{\nu}$ decay within the standard model. This is a second-order weak process involving two four-Fermi operators that is highly…
This paper summarizes some recent progress and future perspectives in the experimental investigation of the Standard Model (and physics beyond it) using charged kaon decays, except for the important mode K+ -> pi+ nu nubar discussed in…
The decays and mixing of $K$ mesons are remarkably sensitive to the weak interactions of quarks and leptons at high energies. They provide important tests of the standard model at both first and second order in the Fermi constant $G_F$ and…