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We present a complete list of the independent dimension-7 operators that are constructed using the standard model degrees of freedom and are invariant under the standard model gauge group. This list contains only 20 independent operators, far fewer than the 63 operators available at dimension 6. All of these dimension-7 operators contain fermions and violate lepton number, and 7 of the 20 violate baryon number as well. This result extends the standard model effective field theory and allows a more detailed exploration of the structure and properties of possible deformations from the standard model Lagrangian.
Landon Lehman (Tue,) studied this question.