Executive Summary : | The microphysical nature of dark matter continues to remain a mystery. Some of the properties of dark matter that only involve interactions in the dark sector, like self-interactions can only be tested with cosmological observables, by their imprint on the evolution and distribution of structure in the universe. The next decade in astronomy with will be a golden age for understanding properties of dark matter. Self-interactions among dark matter particles alter the structure of dark matter halos, gravitationally bound, virialized systems that form endpoints of structure formation. In particular self-interactions allow dark matter particles to exchange energy and momentum, this allows for the redistribution of energy in the inner regions of a halo. The exact structure of the inner halo is set by ratio mean free path of interaction and the gravitational scale height. An initial core expansion phase is eventually followed by core-collapse. Earlier it was thought that the core-collapse does not set in within the Hubble time for realistic halos, however recent work has shown that in tidal environments the core-collapse can be significantly accelerated. This has significant impact for satellites of our Milky Way and galaxies that live in clusters Clusters as they are living in strong tidal environments of their host halos. Simulations of core-collapse require careful extensions to current state-of-the-art methods of simulating SIDM. In this project I propose to extend simulation methods, based on the PI's current code to simulate velocity-dependent SIDM in the low interaction cross-section regime. The PI will develop and run simulations to make predictions for observed satellites of Milky Way and Massive groups and cluster halos. The second part of the project will involve modelling the effects of baryonic physics into the simulations of self-interacting dark matter. One of the largest complications in constraining the nature of dark matter is the uncertainty in correctly accounting for the impact of baryonic physics, i.e. the impact of the galaxy evolution processes on the dark matter halo. There are effects, like core formation that can also arise from baryonic feedback through supernovae explosion or AGNs. While simulating the vast range of scales remains a challenge, one model their primary impact by a few relevant parameters. This formalism has been developed extensively in context of cold-dark matter, but semi-analytical treatment of baryons has not been done for self-interacting dark matter. In this project, the researcher propose to add a baryonic model to SIDM simulations and build a joint emulator to constrain self-interactions in the presence of baryons. |