Speaker
Description
Constraining the Higgs self-coupling at collider experiments allows us to better understand the shape and properties of the Higgs potential, which is a promising avenue into New Physics beyond the Standard Model (SM). The current experimental uncertainties on the Higgs self-coupling, parametrised by $\kappa_\lambda$, are of $\mathcal{O}(100\%)$, while Higgs couplings to the weak gauge bosons, parametrised by $\kappa_V$, have been constrained to just a few percent. Given that $\kappa_V$ and $\kappa_\lambda$ are correlated quantities beyond the SM, can we ever see New Physics effects in $\kappa_\lambda$, despite the tight experimental bounds on $\kappa_V$? In this project, I explore the limits of the Higgs self-coupling in general extended scalar sectors. In the singlet extension to the SM, I calculate the allowed region in $\kappa_V$-$\kappa_\lambda$ space both analytically and numerically. Distinguishing between the spontaneous and explicit $\mathbb{Z}_2$-breaking cases, we find that the latter causes a deviation in $\kappa_\lambda$ more than 10 times larger than the former. We further derive analytical expressions for the allowed region in $\kappa_V$-$\kappa_\lambda$ in a general $\mathbb{Z}_2$-symmetric extended scalar sector, where an arbitrary combination of electroweak scalar multiplets are added to the SM. In the alignment limit, this reduces to a function of the electroweak charges of the multiplets, the coupling constants in the associated potential, and the masses of the emerging particles. We show this explicitly for the $\mathbb{Z}_2$-symmetric 2-Higgs-Doublet model. Like in the $\mathbb{Z}_2$-symmetric singlet model, $\kappa_V$ imposes more stringent constraints than $\kappa_\lambda$.
