# Vector SIMP dark matter with approximate custodial symmetry

## TL;DR

This paper introduces a new vector SIMP dark matter model with an approximate custodial symmetry, where dark gauge bosons acquire split masses and the charged boson serves as a dark matter candidate, consistent with relic density and experimental constraints.

## Contribution

The paper proposes a novel vector SIMP dark matter framework with an approximate custodial symmetry and detailed phenomenological analysis.

## Key findings

- Charged gauge boson $X_\pm$ as a viable SIMP dark matter candidate.
- Parameter space consistent with relic density and experimental constraints.
- Analysis of collider and direct detection prospects.

## Abstract

We consider a novel scenario for Vector Strongly Interacting Massive Particle (VSIMP) dark matter with local $SU(2)_X\times U(1)_{Z'}$ symmetry in the dark sector. Similarly to the Standard Model, after the dark symmetry is broken spontaneously by the VEVs of dark Higgs fields, the approximate custodial symmetry determines comparable but split masses for $SU(2)_X$ gauge bosons. In this model, we show that $U(1)_{Z'}$-charged gauge boson of $SU(2)_X$ ($X_\pm$) becomes a natural candidate for SIMP dark matter, annihilating through $3\rightarrow 2$ or forbidden $2\rightarrow 2$ annihilations due to gauge self-interactions. On the other hand, the $U(1)_{Z'}$-neutral gauge boson of $SU(2)_X$ achieves the kinetic equilibrium of dark matter through a gauge kinetic mixing between $U(1)_{Z'}$ and Standard Model. We present the parameter space for the correct relic density in our model and discuss in detail the current constraints and projections from colliders and direct detection experiments.