Discriminating power of milli-lensing observations for dark matter models

Abstract

Context. The nature of dark matter (DM) is still under intense debate. Subgalactic scales are particularly critical, as different, currently viable DM models make diverse predictions on the expected abundance and density profile of DM haloes on these scales. Aims. We investigate the ability of subgalactic DM haloes to act as strong lenses on background compact sources, producing gravitational lensing events on milli-arcsecond scales (milli-lenses), for different DM models. For each DM scenario, we explore whether a sample of ∼ 5000 distant sources is sufficient to detect at least one milli-lens. Methods. We developed a semi-analytical model to estimate the milli-lensing optical depth as a function of the source's redshift for various DM models. We employed the Press-Schechter formalism, as well as results from recent N-body simulations to compute the halo mass function, taking into account the appropriate spherically averaged density profile of haloes for each DM model. We treated the lensing system as a point-mass lens and invoked the effective surface mass density threshold to calculate the fraction of a halo that acts as a gravitational lens. We studied three classes of dark matter models: cold DM, warm DM, and self-interacting DM. Results. We find that haloes consisting of warm DM turn out to be optically thin for strong gravitational milli-lensing (zero expected lensing events). Cold DM haloes may produce lensing events depending on the steepness of the concentration-mass relation. Selfinteracting DM haloes can efficiently act as gravitational milli-lenses only if haloes experience gravothermal collapse, resulting in highly dense central cores.

A Self-interacting Dark Matter Solution to the Extreme Diversity of Low-mass Halo Properties

“…In our SIDM scenario, isolated halos are found in both core-expansion and core-collapse phases, yielding an even larger diversity of inner halo profiles than less extreme SIDM models. In parallel, this physics should be detectable in future strong lensing studies using both gravitational imaging and flux-ratio statistics (e.g., see Minor et al 2017;Meneghetti et al 2020Meneghetti et al , 2023Gilman et al 2021Gilman et al , 2023Yang & Yu 2021;Loudas et al 2022;Dhanasingham et al 2023;Zhang et al 2023); observations of MW satellites will also probe our SIDM model, which predicts that a substantial fraction of the low-mass subhalos that host faint dwarf galaxies are core collapsed (e.g., Kaplinghat et al 2019;Correa 2021;Turner et al 2021;Silverman et al 2023;Slone et al 2023;Yang et al 2023a).…”

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

“…A velocity-dependent cross section is naturally realized in particle physics models that feature, e.g., Rutherford or Møller scattering (Feng et al 2009(Feng et al , 2010Buckley & Fox 2010;Loeb & Weiner 2011;Tulin et al 2013;Agrawal et al 2017;Girmohanta & Shrock 2022;Yang & Yu 2022). Moreover, velocity-dependent SIDM models can be tuned to agree with cosmological observables over a wide range of scales and yield novel, scale-dependent effects on structure formation (e.g., Kaplinghat et al 2016;Feng et al 2021;Gilman et al 2021Gilman et al , 2023Yang & Yu 2021;Correa et al 2022;Loudas et al 2022;Meshveliani et al 2023).…”