Little Higgs and precision electroweak tests

All models containing new physics are highly constrained by the electroweak precision tests. In this note I consider the electroweak precision data constraints on Little Higgs models by using a general method based on the effective Lagrangian approach: one eliminates the heavy fields from the Lagrangian via their classical equations of motion in the limit of infinite mass, which means in practice that their mass must be much bigger than mW . In this way one obtains an effective Lagrangian in terms of the Standard model fields, from which we can directly read off the deviations.