The Higgs Trilinear Coupling and the Scale of New Physics for the SM-Axion-Seesaw-Higgs portal inflation (SMASH) Model

In the extended scalar sector of the SMASH (Standard Model - Axion - Seesaw - Higgs portal inflation) framework, we conduct a phenomenological investigation of the observable effects. In a suitable region of the SMASH scalar parameter spaces, we solve the vacuum metastability problem and discuss the one-loop correction to the triple Higgs coupling, $\lambda_{HHH}$. The $\lambda_{HHH}$ and SM Higgs quartic coupling $\lambda_H$ corrections are found to be proportional to the threshold correction. A large $\lambda_{HHH}$ correction ($\gtrsim 5 \%$) implies vacuum instability in the model and thus limits the general class of theories that use threshold correction. We performed a full two-loop renormalization group analysis of the SMASH model. The SMASH framework has also been used to estimate the evolution of lepton asymmetry in the universe.