Light octet scalars, a heavy Higgs and minimal flavour violation

Abstract

It is widely believed that existing electroweak data requires a Standard Model Higgs to be light while electroweak and flavour physics constraints require other scalars charged under the Standard Model gauge couplings to be heavy. We analyze the robustness of these beliefs within a general scalar sector and find both to be incorrect, provided that the scalar sector approximately preserves custodial symmetry and minimal flavour violation (MFV). We demonstrate this by considering the phenomenology of the Standard Model supplemented by a scalar having SU c(3) × SU L(2) × U Y(1) quantum numbers (8,2) 1/2 - which has been argued [13] to be the only kind of exotic scalar allowed by MFV that couples to quarks. We examine constraints coming from electroweak precision data, direct production from LEPII and the Tevatron, and from flavour physics, and find that the observations allow both the Standard Model Higgs and the new scalars to be simultaneously light - with masses ∼ 100GeV, and in some cases lighter. The discovery of such light coloured scalars could be a compelling possibility for early LHC runs, due to their large production cross section, σ ∼ 100pb. But the observations equally allow all the scalars to be heavy (including the Higgs), with masses ∼ 1TeV, with the presence of the new scalars removing the light-Higgs preference that normally emerges from fits to the electroweak precision data. © SISSA 2009.