A dimension-six operator |H|^2|phi|^4 in a U(1)_D singlet extension relaxes the usual Higgs-portal and mixing-angle correlation, enabling strong first-order electroweak phase transitions driven primarily by the singlet VEV.
Improved sphaleron decoupling condition and the Higgs coupling constants in the real singlet-extended SM
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abstract
We improve the sphaleron decoupling condition in the real singlet-extended standard model. The sphaleron energy is obtained using the finite temperature one-loop effective potential with daisy resummation. For moderate values of the model parameters, the sphaleron decoupling condition is found to be $v_C/T_C>(1.1-1.2)$, where $T_C$ denotes a critical temperature and $v_C$ is the corresponding vacuum expectation value of the doublet Higgs field at $T_C$. We also investigate the deviation of the triple Higgs boson coupling from its standard model value in the region where the improved sphaleron decoupling condition is satisfied. As a result of the improvement, the deviation of the triple Higgs boson coupling gets more enhanced. In a typical case, if the Higgs couplings to the gauge bosons/fermions deviate from the SM values by about 3 (10)%, the deviation of the triple Higgs boson coupling can be as large as about 16 (50)%, which is about 4 (8)% larger than that based on the conventional criterion $v_C/T_C>1$.
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Electroweak phase transitions in a $U(1)_D$ extension of the standard model with dimension-six operators: Gravitational waves and LHC signatures
A dimension-six operator |H|^2|phi|^4 in a U(1)_D singlet extension relaxes the usual Higgs-portal and mixing-angle correlation, enabling strong first-order electroweak phase transitions driven primarily by the singlet VEV.