Unitarity bounds on effective field theories at the LHC

Effective Field Theory (EFT) extensions of the Standard Model are tools to compute observables (e.g. cross sections with partonic center-of-mass energy root(S) over cap) as a systematically improvable expansion suppressed by a new physics scale M. If one is interested in EFT predictions in the parameter space where M < root<(S)over cap>, concerns of self-consistency emerge, which can manifest as a violation of perturbative partial-wave unitarity. However, when we search for the effects of an EFT at a hadron collider with center-of-mass energy root S using an inclusive strategy, we typically do not have access to the event-byevent value of root(S) over cap. This motivates the need for a formalism that incorporates parton distribution functions into the perturbative partial-wave unitarity analysis. Developing such a framework and initiating an exploration of its implications is the goal of this work. Our approach opens up a potentially valid region of the EFT parameter space where M << root S. We provide evidence that there exist valid EFTs in this parameter space. The perturbative unitarity bounds are sensitive to the details of a given search, an effect we investigate by varying kinematic cuts.

Automated summary

Effective Field Theory (EFT) is a tool to compute observables in particle physics. When searching for EFT effects at colliders, it is important to consider self-consistency. We propose a new approach that incorporates parton distribution functions into the analysis, and provide evidence for the validity of EFT predictions in certain parameter spaces.