Testing effective Yukawa couplings in Higgs boson searches at the Tevatron and LHC

Abstract

We explore the possibility that, while the Higgs mechanism provides masses to the weak-gauge bosons at the electroweak scale as in the standard model, fermion masses are generated by an unknown mechanism at a higher energy scale. At low energies, the standard model can then be regarded as an effective field theory, where fermion masses explicitly break the electroweak $\mathrm{SU}(2{)}_{\mathrm{L}}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1{)}_{\mathrm{Y}}$ gauge symmetry. If $\ensuremath{\Lambda}$ is the renormalization scale where the renormalized Yukawa couplings vanish, then at energies lower than $\ensuremath{\Lambda}$, effective Yukawa couplings will be radiatively induced by nonzero fermion masses. In this scenario, Higgs boson decays into photons and weak gauge-bosons pairs are in general quite enhanced for a light Higgs. However, depending on $\ensuremath{\Lambda}$, a substantial decay rate into $b\overline{b}$ can arise that can be of the same order as, or larger than, the enhanced $H\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ rate. A new framework for Higgs searches at hadron colliders is outlined, vector-boson fusion becoming the dominant production mechanism at the CERN LHC, with an important role also played by the $WH/ZH$ associated production. A detailed analysis of the Higgs branching fractions and their implications in Higgs searches is provided, versus the energy scale $\ensuremath{\Lambda}$.