Cluster halo shapes in CDM and SIDM models: unveiling the DM particle nature using a weak-lensing approach

Self-interacting dark matter (SIDM) is an alternative to the standard collisionless cold dark matter model (CDM), allowing for interactions between the dark-matter particles through the introduction of a self-scattering cross-section. However, the observable effects between these two scenarios are hard to detect. In this work, we present a detailed analysis of an application of galaxy-galaxy lensing to measure with high precision the shapes of cluster haloes and how this approach can be used to obtain infonnation regarding the nature of the dark-matter particle. Using two sets of simulated data, SIDM and CDM simulations, we compute stacked shear maps centred on several subsets of haloes with masses greater than or similar to 10(13.5) M-circle dot. From these maps, we obtain the quadrupole profiles related to the mean projected elongation of the particle distribution from which the shape parameters are derived. Accounting for a radial shape variation, this technique provides an enhancement of the observed differences between the simulated data sets. In particular, we obtain a higher slope of the power law for the shape-radial relation for the haloes identified in the SIDM simulation, which are rounder towards the centre. Also, as approaching to the mean virial radius, the projected semi-axis ratios converge to similar values than in the CDM simulation. Moreover, we account for the impact of the neighbouring mass, where more strongly elongated distributions are found for the haloes in the SIDM simulation, indicating that under dark matter self interaction, the large-scale structure imprints a more coherent accretion process.