The geometric SMEFT

Abstract: Effective field theories, like the Standard Model Effective Field Theory (SMEFT), are defined by a chosen field content and a set of symmetries, up to a cut off scale $\Lambda$. Usually, in order to perform calculations, gauge independent field re-definitions consistent with the symmetries of the theory are then used to redefine the fields. This procedure results in a fixed (non-redundant) operator basis, that is not itself field re-definition invariant. Recently, an alternative approach of identifying and calculating with field space geometry has been developed. Field redefinition invariants, characterising field space geometry, appear in observables in amplitude perturbations, and have an expansion in terms of local operators. In the case of the SMEFT, calculating via the geometric approach is known as the geoSMEFT. This approach makes it much easier to calculate at high orders in $1/\Lambda$ in the SMEFT, and can directly result in a complete characterisation of an amplitude perturbation in the $1/\Lambda$ expansion. Using the geoSMEFT, several consistent and complete $\mathcal{O}(1/\Lambda^4)$ results are now known. We define the geoSMEFT and demonstrate its use in some examples.