Light composite Higgs and precision electroweak measurements on the Z resonance: An update

TL;DR

The paper investigates whether technicolor theories with techniquarks in higher representations can satisfy electroweak precision constraints on the Z resonance. It analyzes oblique parameters $S$, $T$, and $U$ for a model with two technoflavours in the two-index symmetric representation of $SU_T(2)$ and an extra lepton generation, including non-perturbative corrections and various hypercharge assignments; it predicts a composite Higgs mass of about $m_H = 150$ GeV. Updated precision data broaden the allowed lepton masses at the 68% level, with overlap across cases, while a non-perturbative reduction of technicolor contributions maintains compatibility up to heavy Higgs scenarios; a second mass-branch can arise for certain charge assignments. Overall the results support the viability of walking technicolor scenarios and their compatibility with current precision measurements, including potential dark matter implications from the new lepton sector.

Abstract

We update our analysis of technicolour theories with techniquarks in higher dimensional representations of the technicolour gauge group in the light of the new electroweak precision data on the Z resonance.

Figures (3)

• Figure 1: Standard-model-like charge assignment.Left Panel: The area shaded in black corresponds to the accessible range for $S$ and $T$ with the masses of the extra neutrino and extra electron taken from $m_Z$ to $10 m_Z$. The perturbative estimate for the contribution to $S$ from techniquarks equals $1/2\pi$. The three staggered ellipses are the $90$% confidence level contours for the former global fit to the electroweak precision data Eidelman:2004wy with $U$ kept at $0$. The values of $U$ in our model lie typically between $0$ and $0.05$ whence they are consistent with these contours. These contours from bottom to top are for Higgs masses of $m_H = 117$, $340$, $1000$ GeV, respectively. The smaller ellipse to the upper right is the 68% confidence level contour for the new global fit to electroweak precision data unknown:2005em with $U=0$ and for a Higgs $m_H=150$ GeV as predicted for our model. Right Panel: With non-perturbative corrections to the $S$ parameter taken into account in the technicolour sector of the theory.
• Figure 2: Leptons with integer charges.Left Panel: The parabolic area shaded in black corresponds to the accessible range for $S$ and $T$ with the masses of the extra neutrino and extra electron taken from $m_Z$ to $10 m_Z$. The perturbative estimate for the contribution to $S$ from techniquarks equals $1/2\pi$. The three staggered ellipses are the $90$% confidence level contours for the former global fit to the electroweak precision data Eidelman:2004wy with $U$ kept at $0$. The values of $U$ in our model lie typically between $0$ and $0.05$ whence they are consistent with these contours. These contours from bottom to top are for Higgs masses of $m_H = 117$, $340$, $1000$ GeV, respectively. The smaller ellipse to the upper right is the 68% confidence level contour for the new global fit to electroweak precision data unknown:2005em with $U=0$ and for a Higgs $m_H=150$GeV as predicted for our model. Right Panel: With non-perturbative corrections to the $S$ parameter taken into account in the technicolour sector of the theory.
• Figure 3: The shaded areas depict the range for the masses of the new leptons which are accessible due to the oblique corrections in accordance with the electroweak precision data without taking into account non-perturbative corrections. $m_1$ ($m_2$) is the mass, in units of $m_Z$, for the lepton with the higher (lower) charge. The black stripes do not correspond exactly to the overlap of the parabolic area with the 68% ellipse in the (S,T)-plane from unknown:2005em but with a polygonal area defined by $-0.1<S+T<+0.5$, $-0.15<S-T<+0.025$, and $S<0.22$. After taking into account non-perturbative corrections subfigures (b) and (c) stay qualitatively the same, while for not too small masses (a) has a second branch with $m_1<m_2$ like in (c). This corresponds to the overlap of the ellipse with the right branch of the parabolic area in Fig. \ref{['smleptons']}b as opposed to Fig. \ref{['smleptons']}a.