Rare and forbidden kaon decays at NA62

A precision lepton universality test by measurement of the helicity suppressed ratio of leptonic decay rates of the charged kaon with ∼ 150000 K± → e±ν decays collected by the NA62 experiment in 2007-08 is presented. The record accuracy of 0.4% constrains the parameter space of new physics models with extended Higgs sector, a fourth generation of quarks and leptons or sterile neutrinos. An improved upper limit on the rate of the lepton number violating decay K± → π±μ±μ±, which probes the resonant enhancement of the rate in the presence of heavy Majorana neutrinos in the ∼ 100 MeV range, is presented. The rare decays K+ → π+νν¯ are excellent processes to make tests of new physics at the highest scale complementary to LHC thanks to their theoretically cleaness. The NA62 experiment at CERN SPS aims to collect of the order of 100 events in two years of data taking, keeping the background at the level of 10%.