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1. Dissipative dark matter on FIRE – I. Structural and kinematic properties of dwarf galaxies

   https://doi.org/10.1093/mnras/stab2042  

   Shen, Xuejian; Hopkins, Philip F; Necib, Lina; Jiang, Fangzhou; Boylan-Kolchin, Michael; Wetzel, Andrew (August 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present the first set of cosmological baryonic zoom-in simulations of galaxies including dissipative self-interacting dark matter (dSIDM). These simulations utilize the Feedback In Realistic Environments galaxy formation physics, but allow the dark matter to have dissipative self-interactions analogous to standard model forces, parametrized by the self-interaction cross-section per unit mass, (σ/m), and the dimensionless degree of dissipation, 0 < fdiss < 1. We survey this parameter space, including constant and velocity-dependent cross-sections, and focus on structural and kinematic properties of dwarf galaxies with $$M_{\rm halo} \sim 10^{10-11}{\, \rm M_\odot }$$ and $$M_{\ast } \sim 10^{5-8}{\, \rm M_\odot }$$. Central density profiles (parametrized as ρ ∝ rα) of simulated dwarfs become cuspy when $$(\sigma /m)_{\rm eff} \gtrsim 0.1\, {\rm cm^{2}\, g^{-1}}$$ (and fdiss = 0.5 as fiducial). The power-law slopes asymptote to α ≈ −1.5 in low-mass dwarfs independent of cross-section, which arises from a dark matter ‘cooling flow’. Through comparisons with dark matter only simulations, we find the profile in this regime is insensitive to the inclusion of baryons. However, when $$(\sigma /m)_{\rm eff} \ll 0.1\, {\rm cm^{2}\, g^{-1}}$$, baryonic effects can produce cored density profiles comparable to non-dissipative cold dark matter (CDM) runs but at smaller radii. Simulated galaxies with $$(\sigma /m) \gtrsim 10\, {\rm cm^{2}\, g^{-1}}$$ and the fiducial fdiss develop significant coherent rotation of dark matter, accompanied by halo deformation, but this is unlike the well-defined thin ‘dark discs’ often attributed to baryon-like dSIDM. The density profiles in this high cross-section model exhibit lower normalizations given the onset of halo deformation. For our surveyed dSIDM parameters, halo masses and galaxy stellar masses do not show appreciable difference from CDM, but dark matter kinematics and halo concentrations/shapes can differ. 

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2. Prospects for measuring dark matter microphysics with observations of dwarf spheroidal galaxies

   https://doi.org/10.1088/1475-7516/2021/07/030  

   Baxter, Eric J.; Kumar, Jason; Pace, Andrew B.; Runburg, Jack (July 2021, Journal of Cosmology and Astroparticle Physics)

   Abstract Dark matter annihilation in dwarf spheroidal (dSph) galaxies near the Milky Way has the potential to produce a detectable signature in gamma-rays. The amplitude of this signal depends on the dark matter density in a dSph, the dark matter particle mass, the number of photons produced in an annihilation, and the possibly velocity-dependent dark matter annihilation cross section. We argue that if the amplitude of the annihilation signal from multiple dSphs can be measured, it is possible to determine the velocity-dependence of the annihilation cross section. However, we show that doing so will require improved constraints on the dSph density profiles, including control of possible sources of systematic uncertainty. Making reasonable assumptions about future improvements, we make forecasts for the ability of current and future experiments — including Fermi, CTA and AMEGO — to constrain the dark matter annihilation velocity dependence. 

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3. 2HDM singlet portal to dark matter

   https://doi.org/10.1007/JHEP01(2021)123  

   Cabrera, M. E.; Casas, J. A.; Delgado, A.; Robles, S. (January 2021, Journal of High Energy Physics)

   null (Ed.)

   A bstract Higgs portal models are the most minimal way to explain the relic abundance of the Universe. They add just a singlet that only couples to the Higgs through a single parameter that controls both the dark matter relic abundance and the direct detection cross-section. Unfortunately this scenario, either with scalar or fermionic dark matter, is almost ruled out by the latter. In this paper we analyze the Higgs-portal idea with fermionic dark matter in the context of a 2HDM. By disentangling the couplings responsible for the correct relic density from those that control the direct detection cross section we are able to open the parameter space and find wide regions consistent with both the observed relic density and all the current bounds. 

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4. Improved constraints on dark matter annihilations around primordial black holes

   https://doi.org/10.1007/JHEP07(2024)273  

   Chanda, Prolay; Scholtz, Jakub; Unwin, James (July 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> Cosmology may give rise to appreciable populations of both particle dark matter and primordial black holes (PBH) with the combined mass density providing the observationally inferred value Ω_DM≈ 0.26. Early studies highlighted that scenarios with both particle dark matter and PBH are strongly excluded byγ-ray limits for particle dark matter with a velocity independent thermal cross section 〈σν〉 ~ 3 × 10⁻²⁶cm³/s, as is the case for classic WIMP dark matter. Here we examine the limits from di useγ-rays on velocity-dependent, including annihilations which arep-wave with 〈σν〉 ∝v²ord-wave 〈σν〉 ∝v⁴, which we find to be considerably less constraining. This work also utilizes a refined treatment of the PBH dark matter density profile. Importantly, we highlight that even if the freeze-out process isp-wave it is typical for (loop/phase-space) suppresseds-wave processes to actually provide the leading contributions to the experimentally constrainedγ-ray flux from the PBH halo. 

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5. Measurement of anti-3He nuclei absorption in matter and impact on their propagation in the Galaxy

   https://doi.org/10.1038/s41567-022-01804-8  

   Acharya, S.; Adamová, D.; Adler, A.; Adolfsson, J.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahmad, S.; Ahn, S. U.; et al (January 2023, Nature Physics)

   Abstract In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ momentum from 25% to 90% for cosmic-ray sources. The results indicate that $${}^{3}\overline{{{{\rm{He}}}}}$$ 3 He ¯ nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation. 

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