Invisible KL decays in the SM extensions

In the Standard Model (SM), the branching ratio for the decay K-L -> vD is helicity suppressed and predicted to be very small <= O(10(-17)). We consider two natural extensions of the SM as the two-Higgs-doublet model (2HDM) and the neutrino minimal Standard Model (vMSM) with additional singlet scalar, whose main feature is that they can lead to an enhanced Br (K-L -> invisible). In the 2HDM, the smallness of the neutrino mass is explained due to the smallness of the second Higgs doublet vacuum expectation value. Moreover, the vMSM extension with additional singlet field can explain the (g-2)(mu) anomaly. The considered models demonstrate that the K-L -> invisible decay is a clean probe of new physics scale well above 100 TeV, that is complementary to rare K -> pi + invisible decay, and provide a strong motivation for its sensitive search in a near future low-energy experiment.