Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Big Corrections from a Little Higgs

C. Csaki, J. Hubisz, G. D. Kribs, P. Meade, J. Terning

TL;DR

This paper analyzes precision electroweak constraints on the littlest Higgs model based on SU(5)/SO(5) at tree level. By integrating out heavy gauge bosons and incorporating a triplet Higgs VEV, the authors derive how heavy states modify light-gauge couplings and four-fermion interactions, mapping these effects onto EW observables via an effective field theory. A global fit to 21 EW data sets yields lower bounds on the symmetry-breaking scale $f$ (around 4 TeV or higher, depending on gauge couplings) and reveals that substantial fine-tuning would still be required to keep a light Higgs mass near 200 GeV. The analysis also highlights parameter regions where triplet-induced effects cancel partial contributions from heavy bosons, though such regions are limited and constrained by stability and LEP data.

Abstract

We calculate the tree-level expressions for the electroweak precision observables in the SU(5)/SO(5) littlest Higgs model. The source for these corrections are the exchange of heavy gauge bosons, explicit corrections due to non-linear sigma-model dynamics and a triplet Higgs VEV. Weak isospin violating contributions are present because there is no custodial SU(2) global symmetry. The bulk of these weak isospin violating corrections arise from heavy gauge boson exchange while a smaller contribution comes from the triplet Higgs VEV. A global fit is performed to the experimental data and we find that throughout the parameter space the symmetry breaking scale is bounded by f > 4 TeV at 95% C.L. Stronger bounds on f are found for generic choices of the high energy gauge couplings. We find that even in the best case scenario one would need fine tuning of less than a percent to get a Higgs mass as light as 200 GeV.

Big Corrections from a Little Higgs

TL;DR

This paper analyzes precision electroweak constraints on the littlest Higgs model based on SU(5)/SO(5) at tree level. By integrating out heavy gauge bosons and incorporating a triplet Higgs VEV, the authors derive how heavy states modify light-gauge couplings and four-fermion interactions, mapping these effects onto EW observables via an effective field theory. A global fit to 21 EW data sets yields lower bounds on the symmetry-breaking scale (around 4 TeV or higher, depending on gauge couplings) and reveals that substantial fine-tuning would still be required to keep a light Higgs mass near 200 GeV. The analysis also highlights parameter regions where triplet-induced effects cancel partial contributions from heavy bosons, though such regions are limited and constrained by stability and LEP data.

Abstract

We calculate the tree-level expressions for the electroweak precision observables in the SU(5)/SO(5) littlest Higgs model. The source for these corrections are the exchange of heavy gauge bosons, explicit corrections due to non-linear sigma-model dynamics and a triplet Higgs VEV. Weak isospin violating contributions are present because there is no custodial SU(2) global symmetry. The bulk of these weak isospin violating corrections arise from heavy gauge boson exchange while a smaller contribution comes from the triplet Higgs VEV. A global fit is performed to the experimental data and we find that throughout the parameter space the symmetry breaking scale is bounded by f > 4 TeV at 95% C.L. Stronger bounds on f are found for generic choices of the high energy gauge couplings. We find that even in the best case scenario one would need fine tuning of less than a percent to get a Higgs mass as light as 200 GeV.

Paper Structure

This paper contains 5 sections, 58 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The Littlest Higgs Model at Tree-Level
  3. The Low-energy Effective Action
  4. The Contributions to Electroweak Observables
  5. Results and Interpretation

Figures (3)

  • Figure 1: The region of parameters excluded to 68%, 95%, and 99% C.L. is shown as a function of $c'$. The parameter $c$ was allowed to vary between $0.1 < c < 0.995$ for each $c'$ to give the least restrictive bound on $f$. (See also Fig. \ref{['contour-fig']}.)
  • Figure 2: The region of parameters excluded to 95% C.L. is shown as a function of $c'$. The region below the contours is excluded to 95% C.L. for $c$ equal to $0.1$ (solid), $0.5$ (dotted), $0.7$ (dashed), $0.99$ (dot-dashed). The shaded region is excluded for any choice of $c$.
  • Figure 3: The difference between the predicted and the experimentally measured values for four observables in standard deviations (the pull). In both figures the decay constant was fixed to $f=4$ TeV. The figure on the left (right) has a fixed $c=0.1$ ($c=0.99$); other values interpolate between these two figures. Notice that the observable that gives the largest contribution varies depending on $c'$.