A Geometric Formulation of Higgs Effective Field Theory: Measuring the Curvature of Scalar Field Space

Abstract

A geometric formulation of Higgs Effective Field Theory (HEFT) is presented. Experimental observables are given in terms of geometric invariants of the scalar sigma model sector such as the curvature of the scalar field manifold $\mathcal M$. We show how the curvature can be measured experimentally via Higgs cross-sections, $W_L$ scattering, and the $S$ parameter. The one-loop action of HEFT is given in terms of geometric invariants of $\mathcal M$. The distinction between the Standard Model (SM) and HEFT is whether $\mathcal M$ is flat or curved, not whether the scalars transform linearly or non-linearly under the electroweak group.

Journal version. The introduction has been rewritten to make clearer the distinction between SM, SMEFT and HEFT. A slight change of notation has been introduced to connect observables with sectional curvature