Searching for Dark Matter and Dark Sectors, Enabling the Sharpest Baby Picture of the Universe with the CMB, and Cluster Cosmology with Rubin/LSST

Title:Searching for Dark Matter and Dark Sectors,Enabling the Sharpest Baby Picture of the Universe with the CMB,and Cluster Cosmology with Rubin/LSST PI: Rouven Essig (Theory)C.N. Yang Institute for Theoretical Physics, Stony Brook University, Stony Brook, NY 11794Co-PI: Neelima Sehgal (Theory)Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794Co-PI: Anja von der Linden (Cosmic Frontier)Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794Essig's Theory proposal focuses on searches for dark matter and dark-sector particles using:  (1) terrestrial probes, and (2) astrophysical and cosmological probes.  Several specific aims are proposed. For (1), these will, e.g., produce novel strategies and predictions for the direct detection of various sub-GeV dark matter candidates, provide state-of-the-art theory calculations for dark-matter and dark-sector particle interactions in materials, enable the discovery/calibration of the Migdal effect, investigate novel low-energy backgrounds, and overall maximize the science of numerous small-scale experiments and detection concepts (e.g., SENSEI, Oscura, searches for Migdal effect). For (2), these will, e.g., develop astrophysical and cosmological predictions of atomic dark matter, explore exotic compact object formation for dissipative dark matter, predict how self-interacting/dissipative dark matter models impact the properties of subhalos and stellar streams, and confront precise predictions for several dark-sector models with data from measurements of Big Bang Nucleosynthesis and the Cosmic Microwave Background. Sehgal's Theory proposal will enable the sharpest picture of the infant Universe and the dark matter structure that subsequently grew within it. This will be accomplished by using Cosmic Microwave Background (CMB) data from experiments including the Simons Observatory (SO), CMB-S4, and CMB-HD.  Sehgal will focus on two main tasks:(1)~to investigate how well baryonic effects that move around the dark matter can be separated from effects intrinsic to dark matter that does not behave as predicted by the cold dark matter model,and (2) to explore new physics probed by the CMB in general, and in synergy with upcoming galaxy surveys. In this way, the science from upcoming SO and CMB-S4 can be maximized.  In addition, this proposal will further the development of the CMB-HD concept by demonstrating the feasibility of its science goals and expanding its science case. For von der Linden (Cosmic Frontier), the next 4 years span the critical period of Commissioning and Early Science with Rubin/LSST.  She proposes to: (1) contribute to the Commissioning process, including investigating the performance of the detection and deblending algorithms, as well as galaxy photometry and photometric redshift estimates, and facilitating the communication between DESC and Rubin Project by serving on the DESC Technical Coordinator team; (2) continue work on identifying unrecognized blends using machine learning, addressing the fact that a majority of LSST objects will be blended, by using LSST sky areas with overlapping space-based imaging to train ML classifiers to reject a significant fraction of unrecognized blends over the entire LSST area; and (3) investigate observational proxies of halo orientation along the line of sight, in order to measure the impact of projection effects, the currently dominant systematic uncertainty for optical cluster observables.