Limits on a Composite Higgs Boson

TL;DR

A fit to precision electroweak data is performed and it is found that a Higgs mass up to 500 GeV is allowed.

Abstract

Precision electroweak data are generally believed to constrain the Higgs boson mass to lie below approximately 190 GeV at 95% confidence level. The standard Higgs model is, however, trivial and can only be an effective field theory valid below some high energy scale characteristic of the underlying non-trivial physics. Corrections to the custodial isospin violating parameter T arising from interactions at this higher energy scale dramatically enlarge the allowed range of Higgs mass. We perform a fit to precision electroweak data and determine the region in the (m_H, Delta T) plane that is consistent with experimental results. Overlaying the estimated size of corrections to T arising from the underlying dynamics, we find that a Higgs mass up to 500 GeV is allowed. We review two composite Higgs models which can realize the possibility of a phenomenologically acceptable heavy Higgs boson. We comment on the potential of improvements in the measurements of m_t and M_W to improve constraints on composite Higgs models.

Figures (2)

• Figure 1: 68% and 95% CL bounds in the $(m_H,\Delta T)$ plane allowed by a fit to precision electroweak data MoriondewwgLEPEWWG. The best fit "standard model" value is shown by the cross on the $\Delta T=0$ line. (Also shown by the dot-dash curve is the contour corresponding to $\Delta \chi^2=4$, whose intersection with the line $\Delta T=0$ -- at approximately 190 GeV -- corresponds to the usual 95% CL upper bound quoted on the Higgs boson mass in the standard model.) The light region to the right is excluded by eqn. \ref{['tmhestimate']} for $b\kappa^2 = 4\pi$. The dark region denotes the additional area excluded for $b\kappa^2=4\pi^2$. The positive branches of the curves bounding these regions are lower bounds for $\Delta T$ in the top-seesaw and composite higgs models described in the text. Any $(m_H, \Delta T)$ with positive $\Delta T$ and to the left of the appropriate triviality curve can be realized in the corresponding model.
• Figure 2: Prospective 68% and 95% CL bounds in $(m_H,\Delta T)$ plane allowed by fit to precision electroweak data LEPEWWG assuming uncertainty in $M_W$ is reduced to 30 MeV and uncertainty in $m_t$ is reduced 2 GeV, as may be possible during Run II of the Fermilab Tevatron. All curves are as described in Figure 1.