Model-Independent Global Constraints on New Physics

TL;DR

This work develops a model-independent framework to constrain heavy new physics via an effective Lagrangian with operators of dimension up to five. It systematically diagonalizes and normalizes the EFT, re-expresses results in standard electroweak parameters, and performs a comprehensive global fit to electroweak data, revealing that most operators are tightly bounded while several FCNC and CP-violating terms remain comparatively weakly constrained. The analysis highlights the utility of a broad operator survey for diagnosing potential new physics and for translating constraints to specific beyond-SM models, including scenarios with exotic-fermion mixing. The resulting constraints provide a unified, conservative benchmark that any beyond-SM theory must satisfy when matched onto the low-energy EFT framework.

Abstract

Using effective-lagrangian techniques we perform a systematic survey of the lowest-dimension effective interactions through which heavy physics might manifest itself in present experiments. We do not restrict ourselves to special classes of effective interactions (such as `oblique' corrections). We compute the effects of these operators on all currently well-measured electroweak observables, both at low energies and at the $Z$ resonance, and perform a global fit to their coefficients. Despite the fact that a great many operators arise in our survey, we find that most are quite strongly bounded by the current data. We use our survey to systematically identify those effective interactions which are {\it not} well-bounded by the data -- these could very well include large new-physics contributions. Our results may also be used to efficiently confront specific models for new physics with the data, as we illustrate with an example.