Alignment Limit in 2HDM: Robustness put to test

TL;DR

This paper examines how higher-dimensional operators can obscure the true alignment limit in two-Higgs-doublet models, potentially invalidating the assumption of exact alignment in certain parameter regions.

Contribution

It investigates the impact of bosonic operators on the alignment limit in 2HDM, revealing that these operators can significantly alter the model's parameter space and challenge the notion of exact alignment.

Findings

Bosonic operators can mask the true alignment in 2HDM.

Electroweak constraints limit some operators but others can still modify the parameter space.

Exact alignment can be excluded at 95% CL due to these operators.

Abstract

In a two-Higgs-doublet model (2HDM), at the vicinity of the alignment limit, the extra contributions to the couplings of the SM-like Higgs with other particles can be subdominant to the same coming from the six dimensional operators. In this context, we revisit the alignment limit itself. It is investigated to what extent these operators can mask the actual alignment in a 2HDM. The bosonic operators which rescale the Higgs kinetic terms can lead to substantial change in the parameter space of the model. We find that some other bosonic operators, which are severely constrained from the electroweak precision tests, can also modify the parameter space of 2HDM due to their anomalous momentum structures. A particular kind of Little Higgs model is explored as an example of 2HDM effective field theory in connection with 2HDM alignment. Choosing a suitable benchmark point in a Type-II 2HDM, we highlight the possibility that the exact alignment limit is ruled out at 95% CL in presence of such operators.