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$B\to K^{(*)}ν\barν$ decays in the Standard Model and beyond

We present an analysis of the rare exclusive $B$ decays $B\to Kν\barν$ and $B\to K^{*}ν\barν$ within the Standard Model (SM), in a model-independent manner, and in a number of new physics (NP) models. Combining new form factor determinations from lattice QCD with light-cone sum rule results and including complete two-loop electroweak corrections to the SM Wilson coefficient, we obtain the SM predictions $\text{BR}(B^+\to K^+ν\barν) = (4.0 \pm 0.5) \times 10^{-6}$ and $\text{BR}(B^0\to K^{* 0}ν\barν) = (9.2\pm1.0) \times 10^{-6}$, more precise and more robust than previous estimates. Beyond the SM, we make use of an effective theory with dimension-six operators invariant under the SM gauge symmetries to relate NP effects in $b\to sν\barν$ transitions to $b\to s\ell^+\ell^-$ transitions and use the wealth of experimental data on $B\to K^{(*)}\ell^+\ell^-$ and related modes to constrain NP effects in $B\to K^{(*)}ν\barν$. We then consider several specific NP models, including $Z'$ models, the MSSM, models with partial compositeness, and leptoquark models, demonstrating that the correlations between $b\to sν\barν$ observables among themselves and with $B_s\toμ^+μ^-$ and $b\to s\ell^+\ell^-$ transitions offer powerful tests of NP with new right-handed couplings and non-MFV interactions.