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Register a new userSelf-Interacting Dark Matter and the Excess of Small-Scale Gravitational Lenses
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Recently, Meneghetti et al. reported an excess of small-scale gravitational lenses in galaxy clusters, compared to simulations of standard cold dark matter (CDM). We propose a self-interacting dark matter (SIDM) scenario, where a population of subhalos in the clusters experiences gravothermal collapse. Using controlled N-body simulations, we show the presence of early-type galaxies in substructures accelerates gravothermal evolution and a collapsed SIDM subhalo has a steeper density profile than its CDM counterpart, leading to a larger radial galaxy-galaxy strong lensing cross section and more lens images, in better agreement with the observations. Our results indicate that strong gravitational lensing can provide a promising test of the self-interacting nature of dark matter.
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Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments like galaxy clusters is studied theoretically using cosmological simulations. Observed gravitational lensing is used to test and characterize the properties of substructures - the small-scale distribution of dark matter - in clusters. An apt metric, the probability of strong lensing events produced by dark matter substructure, is devised and computed for 11 galaxy clusters. We report that observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that hitherto undiagnosed systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results.
We propose a self-interacting boosted dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. The Standard Model has been extended with two vector-like fermion singlets charged under a dark $U(1)_D$ gauge symmetry to describe the dark sector. While the presence of light vector boson mediator leads to sufficient DM self-interactions to address the small scale issues of cold dark matter, the model with GeV scale DM can explain the XENON1T excess via scattering of boosted DM component with electrons at the detector. The requirement of large annihilation rate of heavier DM into the lighter one for sufficient boosted DM flux leads to suppressed thermal relic abundance. A hybrid setup of thermal and non-thermal contribution from late decay of a scalar can lead to correct relic abundance. All these requirements leave a very tiny parameter space for sub-GeV DM keeping the model very predictive for near future experiments.
We propose a self-interacting inelastic dark matter (DM) scenario as a possible origin of the recently reported excess of electron recoil events by the XENON1T experiment. Two quasi-degenerate Majorana fermion DM interact within themselves via a light hidden sector massive gauge boson and with the standard model particles via gauge kinetic mixing. We also consider an additional long-lived singlet scalar which helps in realising correct dark matter relic abundance via a hybrid setup comprising of both freeze-in and freeze-out mechanisms. While being consistent with the required DM phenomenology along with sufficient self-interactions to address the small scale issues of cold dark matter, the model with GeV scale DM can explain the XENON1T excess via inelastic down scattering of heavier DM component into the lighter one. All these requirements leave a very tiny parameter space keeping the model very predictive for near future experiments.
We perform a series of controlled N-body simulations to study realizations of the recently discovered Antlia 2 galaxy in cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. Our simulations contain six benchmark models, where we vary the initial halo concentration and the self-scattering cross section. We adopt well-motivated initial stellar and halo masses, and our fiducial orbit has a small pericenter. After evolving in the Milky Ways tidal field, the simulated galaxies experience significant mass loss and their stellar distributions expand accordingly. These tidal effects are more prominent if the initial halo concentration is lower and if the self-scattering cross section is larger. Our results show that Antlia 2-like galaxies could be realized in CDM if the halo concentration is low and the stellar distribution is diffuse at the infall time, while these conditions could be relaxed in SIDM. We also find all the simulated galaxies predict approximately the same stellar velocity dispersion after imposing selection criteria for stellar particles. This has important implications for testing dark matter models using tidally disturbed systems.
The nature of the dark matter can affect the collapse time of dark matter haloes, and can therefore be imprinted in observables such as the stellar population ages and star formation histories of dwarf galaxies. In this paper we use high resolution hydrodynamical simulations of Local Group-analogue (LG) volumes in cold dark matter (CDM), sterile neutrino warm dark matter (WDM) and self-interacting dark matter (SIDM) models with the EAGLE galaxy formation code to study how galaxy formation times change with dark matter model. We are able to identify the same haloes in different simulations, since they share the same initial density field phases. We find that the stellar mass of galaxies depends systematically on resolution, and can differ by as much as a factor of two in haloes of a given dark matter mass. The evolution of the stellar populations in SIDM is largely identical to that of CDM, but in WDM early star formation is instead suppressed. The time at which LG haloes can begin to form stars through atomic cooling is delayed by $sim$200~Myr in WDM models compared to CDM. It will be necessary to measure stellar ages of old populations to a precision of better than 100~Myr, and to address degeneracies with the redshift of reionization -- and potentially other baryonic processes -- in order to use these observables to distinguish between dark matter models.
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