# Doubly Blind Spots in Scalar Dark Matter Models

## TL;DR

This paper explores a scalar dark matter model with a second Higgs doublet and a singlet, revealing 'blind spots' where collider and direct detection experiments cannot observe dark matter due to cancellations in interactions.

## Contribution

It identifies and analytically characterizes the conditions leading to blind spots in scalar dark matter models with a two-Higgs doublet and singlet, across various model realizations.

## Key findings

- Blind spots occur in collider and direct detection experiments.
- Analytical formulas describe blind spot locations in parameter space.
- Blind spots are generic across different two-Higgs doublet scenarios.

## Abstract

We consider a framework where the Standard Model is augmented by a second SU(2) scalar doublet and by a real scalar singlet that, protected by a Z2 symmetry, provides a particle Dark Matter candidate. We show that this setup allows for doubly blind spots at both collider searches for anomalies in the Higgs invisible decay width, and at direct Dark Matter detection. The blind spots originate from cancellations between interfering diagrams featuring different neutral scalar exchanges, and from cancellations driven by the two-Higgs doublet structure in the vertex coupling the singlet state with the Standard-Model-like Higgs. We demonstrate that the blind spots arise in a wide and generic array of realizations for the two-Higgs doublet model, including scenarios with a non-trivial flavor structure. We provide analytical formul{\ae} that describe the location of the blind spots in the theory parameter space, and we discuss the resulting phenomenology.