Abstract
We present a model describing the dark sector (DS) featured by two interactions remaining efficient until late times in the matter-dominated era after recombination: the interaction among dark radiations (DR), and the interaction between a small fraction of dark matter and dark radiation. The dark sector consists of (1) a dominant component cold collisionless DM (DM1), (2) a sub-dominant cold DM (DM2) and (3) a self-interacting DR. When a sufficient amount of DR is ensured and a few percent of the total DM density is contributed by DM2 interacting with DR, this set-up is known to be able to resolve both the Hubble and σ8 tension. In light of this, we propose a scenario which is logically natural and has an intriguing theoretical structure with a hidden unbroken gauge group SU(5)X ⊗ U(1)X. Our model of the dark sector does not introduce any new scalar field, but contains only massless chiral fermions and gauge fields in the ultraviolet (UV) regime. As such, it introduces a new scale (DM2 mass, mDM2) based on the confinement resulting from the strong dynamics of SU(5)X. Both DM2-DR and DR-DR interactions are attributed to an identical long range interaction of U(1)X. We show that our model can address the cosmological tensions when it is characterized by gX = mathcal{O} (10−3)– mathcal{O} (10−2), mDM2 = mathcal{O} (1)– mathcal{O} (100) GeV and TDS/TSM ≃ 0.3–0.4 where gX is the gauge coupling of U(1)X and TDS(TSM) is a temperature of the DS (Standard Model sector). Our model explains candidates of DM2 and DR, and DM1 can be any kind of CDM.
Highlights
Among many resolutions taking advantage of hypothetical new dark sector (DS) physics,2 interesting is to consider the DS featured by two interactions among dark radiations (DR), and between DR and DM
We present a model describing the dark sector (DS) featured by two interactions remaining efficient until late times in the matter-dominated era after recombination: the interaction among dark radiations (DR), and the interaction between a small fraction of dark matter and dark radiation
DM1 can be any kind of CDM candidates in particle physics
Summary
We make a brief review of the physics underlying a resolution to the Hubble tension and the σ8 tension which we attend to in this letter by referring to refs. [41, 42, 52, 53, 60]. We make a brief review of the physics underlying a resolution to the Hubble tension and the σ8 tension which we attend to in this letter by referring to refs. The resolution assumes that the DS contains both of the DM and the DR. The DR is fluid-like species with a hypothesized non-gravitational self-interaction. The presence of a non-gravitational interaction between DM and DR is assumed as well. Each of non-gravitational interactions among DRs themselves and between DM and DR is the essential physics resolving both of the cosmological tensions as discussed below
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