FCNCs in left-right symmetric theories and constraints on the right-handed scale

We revise the limits on the FCNC Higgs bosons in manifestly left-right symmetric theories. It is shown that the combination of Kobayashi-Maskawa [Formula presented] violation with tree-level [Formula presented] Higgs boson exchange gives a very large contribution to the [Formula presented]-violating [Formula presented] parameter. It leads to a new strong constraint on the FCNC Higgs boson mass, [Formula presented]–100 TeV, enhanced by a factor of the order of [Formula presented]. Being addressed to the supersymmetric left-right models, the FCNC problem requires that both the right-handed scale and supersymmetric mass parameters be heavier than [Formula presented] TeV for [Formula presented]. The most relaxed case corresponds to [Formula presented]–30 where the right-handed scale can be of the order of a few TeV.