Top quark decays into neutral Higgs bosons and gluon in the MSSM

Abstract

Flavour changing neutral decays of the top quark are know to be extremely suppressed in the SM. This is especially so for the top quark decay into the SM Higgs boson, whose rate is less than 10^-13. However, it turns out that the decay modes t->c h, with h= h^0,H^0,A^0 any of the MSSM neutral Higgs bosons, can be much more gifted. In particular, the rate into the lightest CP-even Higgs boson h^0 -- which is an accessible decay mode across the whole MSSM parameter space -- is generally higher than the decay into glue, t->c g, even though the latter can also be considerably augmented in the MSSM. Our general conclusion is that the Higgs channel t->c h^0 can be the ``gold-plated'' top quark FCNC decay mode in the MSSM with rates that can reach 10^-4, i.e. already at the visible level for both LHC and LC.