Title:Â General Form of Effective Operators from Portals to Hidden Sectors
Abstract: I discuss a model-independent analysis of the dimension-six termsÂ that are generated in the low energy effective theory when a hidden sector thatÂ communicates with the Standard Model through a specific portal operator is integrated out. I work within the Standard Model Effective Field Theory (SMEFT)Â framework and consider the Higgs, neutrino, and hypercharge portals. It is shown that,Â for each portal, the forms of the leading dimension-six terms in the low-energy effective theory are fixed and independent of the dynamics in the hiddenÂ sector. For the Higgs portal, two independent dimension-six terms areÂ generated, one of which has a sign that, under certain conditions, is fixed by theÂ requirement that the dynamics in the hidden sector be causal and unitary. In theÂ case of the neutrino portal, for a single generation of SM fermions and assumingÂ that the hidden sector does not violate lepton number, a unique dimension-six termÂ is generated, which corresponds to a specific linear combination of operators in theÂ Warsaw basis. For the hypercharge portal, a unique dimension-six term is generated,Â which again corresponds to a specific linear combination of operators in the WarsawÂ basis. For both the neutrino and hypercharge portals, under certain conditions, theÂ signs of these terms are fixed by the requirement that the hidden sector be causalÂ and unitary. I perform a global fit of these dimension-six terms to electroweak precision observables, Higgs measurements, and diboson production data and determineÂ the current bounds on their coefficients.