LEX-EFT: the Light Exotics Effective Field Theory

Abstract

We propose the creation of a Light Exotics Effective Field Theory (LEX-EFT) catalog. LEX-EFT is a generic framework to capture all interactions between the Standard Model (SM) and all (or at least a large class of) theoretically allowed exotic states beyond the Standard Model (bSM), indexed by their SM and bSM charges. These states are light enough to be on or nearly on shell in some collider processes. This framework, which subsumes beyond the Standard Model paradigms as generally as possible, is meant to extend recent successful implementations of bSM EFTs and complement e.g. the Standard Model Effective Field Theory (SMEFT), which can capture the off-shell effects of exotic fields. In this work, we review a general method for the construction of a complete list of gauge-invariant operators involving SM interactions with light exotics via iterative tensor product decomposition, up to the desired order in mass dimension. Each operator is characterized by specific Clebsch-Gordan coefficients determined by the charge flow; we show how this charge flow affects the range of EFT validity and cross sections associated with an effective operator. We create an example catalog of exotic scalars coupling to SM gauge boson pairs, and we highlight some operators with exotic weak SU(2)L charges that can produce spectacular LHC phenomenology. We further demonstrate the utility of the LEX-EFT approach with several examples of effects on kinematic distributions and cross sections that would not be captured by EFTs agnostic to the exotic degrees of freedom and may evade the main inclusive collider searches tailored to the existing preferred set of standard bSM theories.

Leptonic signatures of color-sextet scalars

“…We take as inspiration several models, both renormalizable and effective, of color octets with non-trivial SU(2) L charge [63][64][65]. These states can be fundamentals, adjoints, or even higher multiplets of SU(2) L [8]. These multiplets contain charged and neutral states and may have various new production modes and subsequently undergo interesting cascade decays [66].…”

“…To take a broader view, new SU(3) c charged states, with their wide range of new signatures, remain ripe for exploration. New operator catalogs would include interesting diboson production modes and decays [8,64,67] and multiple heavy-flavor events [68]. Following the spirit of this work, we plan to explore other novel EFTs involving exotic color-charged states.…”

“…While the number of gauge-invariant renormalizable sextet-SM interactions is small (though even these are rich and worth further attention), there are a large number of effective interactions at relatively low mass dimensions that have just begun to be studied [7]. Effective operators that integrate out some ultraviolet degrees of freedom but retain sextets at the weak or TeV scale themselves constitute but one subclass of a huge collection of operators with light exotics that offer alternative paths to discovery of bSM physics at the LHC [8].…”