The windows for kinetically mixed Z'-mediated dark matter and the galactic center gamma ray excess

TL;DR

This paper investigates fermionic dark matter models with a kinetically mixed Z' gauge boson, analyzing constraints from various experiments and their potential to explain the galactic center gamma ray excess.

Contribution

It provides a comprehensive analysis of parameter space constraints and identifies regions compatible with the gamma ray excess, highlighting differences between Dirac and Majorana dark matter.

Findings

Dirac model can explain the gamma ray excess at 2-3 sigma level.

Constraints vary with kinetic mixing parameter, affecting experimental sensitivity.

Identifies promising regions for future discovery in dark matter parameter space.

Abstract

One of the simplest hidden sectors with signatures in the visible sector is fermionic dark matter $\chi$ coupled to a $Z'$ gauge boson that has purely kinetic mixing with the standard model hypercharge. We consider the combined constraints from relic density, direct detection and collider experiments on such models in which the dark matter is either a Dirac or a Majorana fermion. We point out sensitivity to details of the UV completion for the Majorana model. For kinetic mixing parameter $\epsilon \le 0.01$, only relic density and direct detection are relevant, while for larger $\epsilon$, electroweak precision, LHC dilepton, and missing energy constraints become important. We identify regions of the parameter space of $m_\chi$, $m_{Z'}$, dark gauge coupling and $\epsilon$ that are most promising for discovery through these experimental probes. We study the compatibility of the models with the galactic center gamma ray excess, finding agreement at the 2-3$\sigma$ level for the Dirac model.