Exothermic dark mesons in light of electron recoil excess at XENON1T

TL;DR

This paper proposes a new dark matter model involving dark mesons with small mass splittings, explaining the XENON1T electron recoil excess through inelastic scattering, and demonstrates a viable parameter space fitting experimental data.

Contribution

It introduces a novel mechanism for exothermic dark mesons with a dark U(1)' gauge symmetry, providing a concrete model that explains XENON1T excess and satisfies experimental constraints.

Findings

A parameter space fits XENON1T data with two peaks from exothermic processes.

The model achieves the correct relic density while satisfying experimental constraints.

Small mass splittings between dark mesons enable inelastic scattering explaining electron recoil excess.

Abstract

We consider a novel mechanism to realize exothermic dark matter with dark mesons in the limit of approximate flavor symmetry in a dark QCD. We introduce a local dark $U(1)'$ symmetry to communicate between dark mesons and the Standard Model via $Z'$ portal by partially gauging the dark flavor symmetry with flavor-dependent charges for cancelling chiral anomalies in the dark sector. After the dark local $U(1)'$ is broken spontaneously by the VEV of a dark Higgs, there appear small mass splittings between dark quarks, consequently, leading to small split masses for dark mesons, required to explain the electron recoil excess in XENON1T by the inelastic scattering between dark mesons and electron. We propose a concrete benchmark model for split dark mesons based on $SU(3)_L\times SU(3)_R/ SU(3)_V$ flavor symmetry and $SU(N_c)$ color group and show that there exists a parameter space making a better fit to the XENON1T data with two correlated peaks from exothermic processes and satisfying the correct relic density, current experimental and theoretical constraints.