Little Higgs Models and Precision Electroweak Data

TL;DR

The paper addresses how Little Higgs constructions fare against precision electroweak data by integrating out heavy fields to obtain low-energy effective Lagrangians and computing oblique corrections in the $\epsilon$-framework. It develops and applies a general method to two models: the Littlest Higgs without custodial symmetry and a variant with approximate custodial $SU(2)$ symmetry, deriving the leading corrections of order $v^2/f^2$ to $G_F$, $m_W$, and $m_Z$, and expressing them in terms of mixing angles and triplet vevs. The results show that the custodial-symmetric version broadens the viable parameter space by reducing problematic corrections, while the original Littlest Higgs is tightly constrained for larger $v/f$. The work provides a practical procedure for testing Little Higgs models against precision data and highlights the role of custodial symmetry in maintaining compatibility with electroweak measurements.

Abstract

We study the low energy limit of Little Higgs models. The method consists in eliminating the heavy fields using their classical equations of motion in the infinite mass limit. After the elimination of the heavy degrees of freedom we can directly read off deviations from the precision electroweak data. We also examine the effects on the low energy precision experiments.