This is a repository to collect information related to the study of the fundamental nature of dark matter with LSST. Our goal is to understand the microphysics of dark matter: to identify the fundamental constituents of dark matter (e.g., new fundamental particles, compact objects, etc.), and to characterize the properties of these constituents (e.g, mass, temperature, self-interaction rate, etc.). LSST offers a unique avenue to attack the dark matter problem through "astrophysical probes"; however, there is also a significant overlap with experiments performing direct and indirect searches for dark matter. It is worth emphasizing that, when compared to other cosmological probes and analyses performed within DESC, the dark matter studies here very often focus on the small structures in the dark matter hierarchical clustering, quite complementary to large scale probes for dark energy.

There are many avenues to attack the dark matter problem with LSST. Below is a brief description of some that we have started to consider:

• Local Group Dwarf Galaxies (satsim and satellites): Local Group dwarf galaxies provide the most direct tracer of the low-mass end of the matter power spectrum and are sensitive to deviations from LCDM on the smallest scales.
• Stellar Streams (streamsim]: Perturbations in stellar streams can be used to trace the dark matter subhalo population below the threshold for star formation.
• Strong Lensing Substructures (stronglens): Dark matter substructure can be traced independently of baryons through perturbations in the strong lensing of galaxies at cosmological distances.
• Axion Cooling of Stars (axions): Axions (and other axion-like particles) would provide an alternative thermal transport mechanism altering stellar physics (e.g., white dwarf lifetimes)
• Galaxy Cluster Density Profiles (clusters): Dark matter self-interactions would alter the density profiles in galaxy clusters and could lead to observable offsets between galaxies and dark matter in colliding clusters.
• Microlensing (macho): Searches for massive compact halo objects (MACHOs) using the microlensing of stars.
• Nanolensing (nanolensing): Can we use gravitational lensing to detect dark matter subhaloes directly?

This is certainly not an exhaustive list, and we would be excited to add your new idea! One immediate example concerns the characterization of the Milky Way graviational potential through star orbits, especially the old Carbon-rich population in the outskirts of the Galaxy, that LSST should be able to detect.

• White Paper (doc): We are in the process of writing a white paper to summarize the various avenues to attack the dark matter problem with LSST.
• Living Bibliography (bib): We have started to compile a living bibliography
• Dark Matter Hack Session: The LSST dark matter project began to take form at the LSST DESC April 2017 Hack Week. You can find more information on the results of that hack on Confluence.
• List of Dark Matter Probes (table) One result of the hack week was a high-level list of dark matter probes with LSST.

The study of dark matter with LSST is a rapidly growing field. If you are interested in joining, there are several ways to get involved:

• Join our Slack channel: #lsst-desc-darkmatter
• Join our email list: [email protected]
• Check out our Confluence page: wikipage
• Get in touch with some of the organizers: Alex Drlica-Wagner (@kadrlica), Will Dawson (@wadawson), Keith Bechtol (@bechtol)