  Kaon decay studies seeking new-physics (NP) effects in leptonic (K_l2) or
semileptonic (K_l3) decays are discussed.
  A unitarity test of the first row of the CKM mixing matrix is obtained from
the KLOE precision measurements of Kl3 widths for K^+-, K_L, and (unique to
KLOE) K_S, complemented with the absolute branching ratio for the K_mu2 decay.
  KLOE results lead to constraints for NP models and can probe possible charged
Higgs exchange contribution in SM extensions with two Higgs doublets.
  The main focus in the present document is set on a new measurement of
R_K=Gamma(K_e2)/Gamma(K_mu2) with an accuracy at the % level, aiming at finding
evidence of deviations from the SM prediction induced by lepton-flavor
violation NP effects.
