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× SU(3)R/SU(3)V flavor symmetry and SU(Nc) 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.
Highlights
A definite conclusion on the XENON1T excess
We propose a concrete benchmark model for split dark mesons based on SU(3)L × SU(3)R/SU(3)V flavor symmetry and SU(Nc) 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
We propose a novel mechanism for exothermic dark matter based on the dark flavor symmetry SU(Nf )L × SU(Nf )R/SU(Nf )V for dark quarks in SU(Nc) dark QCD
Summary
We consider dark mesons as light dark matter living on SU(Nf )L × SU(Nf )R/SU(Nf )V flavor symmetry and SU(Nc) color group in the dark sector. We can choose a simple but nontrivial choice, Q 2 = 1, so the charge operator takes +1 or −1 with Tr(Q ) = 0 [14] In this case, some of dark mesons become charged under the U(1). The Lagrangian for dark mesons π, dark gauge boson Z , and dark Higgs φ are given by. The dark meson mass terms in the full Lagrangian in eq (2.1) give rise to extra quartic self-interactions for dark mesons. After the dark Higgs is expanded around a nonzero VEV by φ = (vφ + h )/ 2, Z and the dark Higgs masses are given by mZ = qφgZ vφ and mh = 2λφvφ, in the limit of small mixings with the visible sector. Dark mesons can scatter off the electron through Z -portal for direct detection of dark matter, and dark mesons can pair annihilate into e+e− for determining the relic density
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