Heavy Long-lived Dark Vector Via a Gluonic Portal

TL;DR

This paper explores a long-lived dark gauge boson Z' that couples to gluons via higher-dimensional operators, analyzing its potential as dark matter and its detectability through collider and cosmological observations.

Contribution

It identifies the leading effective operators for a gluon-coupled Z' and studies its phenomenology as both a long-lived particle and a dark matter candidate.

Findings

Z' can be long-lived due to dimension-eight operators.

Mass of Z' > 1 TeV compatible with thermal freeze-out.

Unconstrained parameter space in freeze-in scenario due to tiny couplings.

Abstract

We study a dark gauge boson $ Z' $ that exclusively couples to the QCD gluons through higher dimensional operators. These operators are generated from integrating out of heavy ultraviolet resonances carrying both QCD and dark gauge charges. With $ SU(3)_C $ gauge invariance, charge and parity symmetries preserved, we find that the leading effective operators are restricted to have the form of $ Z'GGG $ and $ Z'Z'GG $ at dimension-eight, which can naturally render the $Z^\prime$ particle long-lived, and serve as a viable dark matter candidate. We investigate the phenomenology of these operators with both collider experiments and cosmological observation, without and with the assumption that this dark gauge boson plays the role of the dominant dark matter component. For an unstable $Z'$, we show that depending on its lifetime, it can be probed by various observables up to ultraviolet physics scale around $10^9$ GeV. For $Z'$ being dark matter, we find that $m_{Z^\prime} \gtrsim 1 $ TeV is consistent with the thermal freeze-out scenario. In contrast, in the freeze-in scenario, the extremely small couplings leave the relevant parameter space largely unconstrained by current experiments.