The electroweak symmetry breaking (EWSB) sector of the standard model can be far richer and more interesting than the usual single scalar doublet model. We explore scenarios where the EWSB sector is nearly scale invariant and consequently gives rise to a light $CP$ even scalar particle. The one-doublet SM is in that category, as are many other models with either weakly or strongly coupled sectors that trigger EWSB. We study the couplings of the light scalar to the SM particles that can arise from the explicit breaking of scale invariance focusing on the possible differences with the minimal SM. The couplings of the light scalar to light fermions, as well as to the massless gauge bosons, can be significantly enhanced. We find possible new discovery channels due to the decays of the conformal scalar into $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ pairs as well as new production channels via light quark annihilation.

• Received 10 September 2008

DOI:https://doi.org/10.1103/PhysRevD.79.035017