Light Octet Scalars, a Heavy Higgs and Minimal Flavour Violation

TL;DR

This paper challenges the common belief that the Standard Model Higgs must be light and other scalars heavy, showing that both can be light or heavy if custodial symmetry and minimal flavour violation are approximately preserved.

Contribution

It demonstrates that light or heavy scalars, including a new exotic scalar, are consistent with current data within a general scalar sector respecting custodial symmetry and MFV.

Findings

Both the Standard Model Higgs and new scalars can be light (~100 GeV) and still fit data.

Scalars can also be heavy (~1 TeV), removing the usual light-Higgs preference.

Light coloured scalars could be produced copiously at the LHC, providing early discovery opportunities.

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(3)_c x SU(2)_L x U(1)_Y quantum numbers (8,2)_(1/2) which has been argued to be the only kind of exotic flavour singlet 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 ~ 100 GeV, 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, ~100 pb. But the observations equally allow all the scalars to be heavy (including the Higgs), with masses ~ 1 TeV, with the presence of the new scalars removing the light-Higgs preference that normally emerges from fits to the electroweak precision data.