# Phenomenology of ELDER Dark Matter

## TL;DR

This paper investigates the phenomenology of ELDER dark matter, a thermal relic whose detection prospects are predicted based on elastic scattering mediated by a dark photon, providing testable targets for future experiments.

## Contribution

It introduces the ELDER dark matter scenario, deriving robust, model-independent predictions for direct detection and dark photon searches, and presents simple models illustrating the mechanism.

## Key findings

- Predictions for electron-recoil direct detection experiments.
- Robust, model-independent signals for dark photon searches.
- Analytic approximations for ELDER-related quantities.

## Abstract

We explore the phenomenology of Elastically Decoupling Relic (ELDER) dark matter. ELDER is a thermal relic whose present density is determined primarily by the cross-section of its elastic scattering off Standard Model (SM) particles. Assuming that this scattering is mediated by a kinetically mixed dark photon, we argue that the ELDER scenario makes robust predictions for electron-recoil direct-detection experiments, as well as for dark photon searches. These predictions are independent of the details of interactions within the dark sector. Together with the closely related Strongly-Interacting Massive Particle (SIMP) scenario, the ELDER predictions provide a physically motivated, well-defined target region, which will be almost entirely accessible to the next generation of searches for sub-GeV dark matter and dark photons. We provide useful analytic approximations for various quantities of interest in the ELDER scenario, and discuss two simple renormalizable toy models which incorporate the required strong number-changing interactions among the ELDERs, as well as explicitly implement the coupling to electrons via the dark photon portal.