Flavour-Changing Decays of a 125 GeV Higgs-like Particle

TL;DR

This paper investigates the potential for observing flavor-changing decays of a 125 GeV Higgs-like particle, finding that lepton-flavor-changing decays could be sizable and detectable, while quark-flavor-changing decays are strongly constrained.

Contribution

It provides the first comprehensive analysis of indirect constraints on flavor-changing Higgs decays from low-energy flavor experiments.

Findings

Quark-flavor-changing Higgs decays are unlikely to be observable at the LHC.

Lepton-flavor-changing decays could have branching ratios of order 10%.

Such lepton-flavor-changing decays are potentially detectable at the LHC.

Abstract

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 $\sim 125$ 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 ${\mathcal B}(h \to \tau \bar \mu + \bar \mu \tau)$ or ${\mathcal B}(h \to \tau \bar e + \bar e \tau) $ could be ${\cal O}(10)%$, i.e., comparable to ${\mathcal B}(h \to \tau^+ \tau^-)$ and potentially observable at the LHC.