Impact of dimension-8 SMEFT operators on baryogenesis via sphaleron decoupling

We investigate whether a baryogenesis mechanism known as sphalerogenesis can account for the observed baryon asymmetry of the Universe within the Standard Model effective field theory. In this scenario, the baryon asymmetry is generated through the $CP$-asymmetric decoupling of electroweak (EW) sphaleron-like transitions. We introduce seven $CP$-violating dimension-8 operators constructed from the Higgs doublet and the $SU(2)_L$ gauge fields and show that five of them can individually account for the observed baryon asymmetry with satisfying experimental constraints from colliders or electron electric dipole moment measurements. We further study their impact in the presence of a $CP$-violating dimension-6 operator. We find that the dimension-8 contributions can be comparable to the dimension-6 contribution when the dimension-8 operators are generated at one loop, demonstrating that loop-order counting can be as important as canonical mass-dimension counting in sphalerogenesis.