When integrating out unknown new physics sectors, what is the minimal
character of the Standard Model Effective Field Theory (SMEFT) that can result?
In this paper we focus on a particular aspect of this question: "How can one
obtain only one dimension six operator in the SMEFT from a consistent tree
level matching onto an unknown new physics sector?" We show why this requires
conditions on the ultraviolet field content that do not indicate a stand alone
ultraviolet complete scenario. Further, we demonstrate how a dynamical origin
of the ultraviolet scales assumed to exist in order to generate the masses of
the heavy states integrated out generically induces more operators. Therefore,
our analysis indicates that the infrared limit captured from a new sector in
consistent matchings induces multiple operators in the SMEFT quite generically.
Global data analyses in the SMEFT can and should accommodate this fact.Comment: 11pp, 2 fig. V2: PLB version and minor typos correcte
