Flavour-changing decays of a 125 GeV Higgs-like particle

The ATLAS and CMS experiments at the LHC have reported the observation of a possible excess of events corresponding to a new particle h with mass ∼125 GeV that might be the long-sought Higgs boson, or something else. Decyphering the nature of this possible signal will require constraining the couplings of the h and measuring them as accurately as possible. Here we analyze the indirect constraints on flavour-changing h decays that are provided by limits on low-energy flavour-changing interactions. We find that indirect limits in the quark sector impose such strong constraints that flavour-changing h decays to quark-antiquark pairs are unlikely to be observable at the LHC. On the other hand, the upper limits on lepton-flavour-changing decays are weaker, and the experimental signatures less challenging. In particular, we find that either B (h → τμbar +μbar τ) or B (h → τebar +ebar τ) could be O (10)%, i.e., comparable to B (h →τ⁺τ^-) and potentially observable at the LHC.