Dissipative hidden sector dark matter

TL;DR

This work proposes a dissipative dark matter scenario in which two stable dark fermions $F_1$ and $F_2$ interact via an unbroken $U(1)'$ gauge symmetry and a dark photon that kinetically mixes with the SM photon ($\epsilon\sim10^{-9}$). It combines early-Universe cosmology and galactic-structure analyses to constrain a five-parameter model $(m_{F_1}, m_{F_2}, \alpha', Z', \epsilon)$, showing that SN heating can offset dissipative dark bremsstrahlung and yield cored halos that reproduce the Tully-Fisher and Faber-Jackson relations. The paper derives bounds from $\delta N_{\text{eff}}$ at CMB/BBN and from dark recombination, and demonstrates a consistent parameter space where the halo dynamics align with observations across galaxy types. These results motivate experimental probes, including direct-detection channels sensitive to $F_1$–electron and $F_2$–nuclei interactions, and potential diurnal modulation signatures in Southern-hemisphere detectors.

Abstract

A simple way of explaining dark matter without modifying known Standard Model physics is to require the existence of a hidden (dark) sector, which interacts with the visible one predominantly via gravity. We consider a hidden sector containing two stable particles charged under an unbroken $U(1)^{'}$ gauge symmetry, hence featuring dissipative interactions. The massless gauge field associated with this symmetry, the dark photon, can interact via kinetic mixing with the ordinary photon. In fact, such an interaction of strength $ε\sim 10 ^{-9}$ appears to be necessary in order to explain galactic structure. We calculate the effect of this new physics on Big Bang Nucleosynthesis and its contribution to the relativistic energy density at Hydrogen recombination. We then examine the process of dark recombination, during which neutral dark states are formed, which is important for large-scale structure formation. Galactic structure is considered next, focussing on spiral and irregular galaxies. For these galaxies we modelled the dark matter halo (at the current epoch) as a dissipative plasma of dark matter particles, where the energy lost due to dissipation is compensated by the energy produced from ordinary supernovae (the core-collapse energy is transferred to the hidden sector via kinetic mixing induced processes in the supernova core). We find that such a dynamical halo model can reproduce several observed features of disk galaxies, including the cored density profile and the Tully-Fisher relation. We also discuss how elliptical and dwarf spheroidal galaxies could fit into this picture. Finally, these analyses are combined to set bounds on the parameter space of our model, which can serve as a guideline for future experimental searches.

Figures (8)

• Figure 1: Evolution of ${\cal X} \equiv T _{\gamma _{_D}}/T _{\gamma}$ for $m_{F_1}=10$ MeV (dot-dashed line), $m_{F_1}=1$ MeV (solid line) and $m_{F_1}=0.1$ MeV (dashed line).
• Figure 2: $\delta N _{\text{eff}}$[CMB] versus $\epsilon$ at fixed values of $m_{F_1}$ for (going from up to down) $m_{F_1}=0.1, 0.511, 0.7, 1, 10$ MeV.
• Figure 3: Exclusion limits obtained from $\delta N _{\text{eff}}$[CMB] $<$ 0.80 in $\epsilon$-$m_{F_1}$ parameter space (excluded region is above line).
• Figure 4: $\delta N _{\text{eff}}$[BBN] versus $\epsilon$ at fixed values of $m_{F_1}$ for (going from up to down) $m _{F_1} = 0.1, 0.7, 1, 2, 10$ MeV.
• Figure 5: Exclusion limits from $\delta N _{\text{eff}}$[CMB] $<$ 0.80 (solid line) and $\delta N _{\text{eff}}$[BBN] $<$ 1 (dashed line). Region above lines are excluded.