Effective Theory of a Dynamically Broken Electroweak Standard Model at NLO

TL;DR

This paper develops a systematic effective field theory framework for a Higgsless Standard Model with a new strong interaction, including complete operator lists up to next-to-leading order, clarifying the power counting and operator relevance.

Contribution

It provides a comprehensive, systematic construction of the electroweak chiral Lagrangian up to NLO without a light Higgs, including operator classification and elimination via equations of motion.

Findings

Complete operator list at leading and next-to-leading order

Power-counting formulas for operator relevance

Confirmation of dimension-6 operators in the Higgs scenario

Abstract

We consider the Standard Model as an effective theory at the weak scale $v$ of a generic new strong interaction that dynamically breaks electroweak symmetry at the energy scale $\Lambda\sim $ (few) TeV. Assuming only the minimal field content with the Standard Model fermions and gauge bosons, but without a light Higgs particle, we construct the complete Lagrangian through next-to-leading order, that is, including terms of order $v^2/\Lambda^2$. The systematics behind this expansion is clarified. Although similar to chiral perturbation theory, it is not governed by the dimension of operators alone, but depends in an essential way on the loop expansion. Power-counting formulas are derived that indicate the classes of operators required at the next-to-leading order. The complete set of operators at leading and next-to-leading order is then listed, based on the restrictions implied by the Standard-Model gauge symmetries. We recover the well-known operators discussed in the literature in connection with the electroweak chiral Lagrangian and in similar contexts, but we collect a complete and systematic list of all terms through order $v^2/\Lambda^2$. This includes some operators not discussed in explicit terms before. We also show that a few of the previously considered operators can be eliminated via the equations of motion. As another important result we confirm the known list of dimension-6 operators in the Standard Model with an elementary Higgs doublet, essentially as a special case of our scenario.