The theory section of the workshop focused started with some general phenomenological considerations that must be addressed by a model of detectable light dark matter. We started with large-scale, cosmological issues such as the production and early universe behavior of light dark matter. Next, we addressed the various ways that such particles could couple to Standard Model systems of interest, including nuclei, electrons, and condensed-matter degrees of freedom. Finally, we concluded with other late-time signatures of light dark matter in the lab and in astrophysical environments.
General Overview
- Light Thermal Dark Matter and Hidden Sectors – Philip Schuster – Slides
Describes the standard process where DM obtains its relic abundance through thermal freeze-out, how this paradigm is adapted for sub-GeV dark matter, and the implications for direct detection and collider experiments. - Freeze-in, Misalignment, and Nonstandard Thermal Histories – Nikita Blinov – Slides
Overview of models where DM obtains its relic abundance without being in thermal equilibrium with the Standard Model at early times, including late freeze-out, freeze-in through an ultralight dark photon, misalignment in various cosmological histories for axions, and other production mechanisms for dark photon dark matter. - Dark Thermal Histories – Jessie Shelton – Slides
Overview of different possibilities for relationships between the temperature of a dark sector and the Standard Model temperature, including asymmetric reheating, thermal contact from the Standard Model, and implications for CMB constraints and direct detection. - Energy Injection Constraints from the CMB and How to Evade Them – Sam McDermott – Slides
Review of constraints from residual ionization of hydrogen at time of CMB and implications for sub-GeV dark matter models, including hidden sectors, asymmetric DM, and freeze-in.
Theory of Interactions
- Dark Matter Electron Scattering and Electronic Excitation – Tien-Tien Yu – Slides
Review of kinematics of DM scattering from electrons in bound states, including isolated atoms and crystals. - Dark Matter Induced Phonon Excitations – Tongyan Lin – Slides
Review of kinematics of DM-ion scattering in crystal lattices which produce phonons, including single phonon excitation (optical and acoustic), multiphonon excitations in superfluid helium, and anisotropic effects - Dark Matter Atom Interactions – Oren Slone – Slides
Review of DM interactions in composite atomic systems, including vibrational excitations in molecules, the Migdal effect, absorption of bosonic DM, and color centers from ionic displacement
New Ideas
- Inducing and Detecting Collective Effects of Particle Dark Matter – Asher Berlin – Slides
Suggests a technique for probing new parameter space in a specific model wherein dark matter has a small charge under Standard Model electromagnetism. The dark matter can be manipulated by oscillating electric plates and the “wind” downstream will have unique and easily detectable signatures. - Light Strongly Interacting Dark Matter – Chris Kouvaris
Discusses the possibility of a “blind spot” in direct detection experiments if dark matter interacts so strongly that it is unable to penetrate the earth’s atmosphere and soil. - Constraints on Sub-GeV Dark Matter from Cosmology – Vera Glusevic – Slides
Discusses constraints on dark matter that is interacts strongly with baryons from cosmology and astrophysics. One strong and oft-considered probe (treated here in great detail) is from tight coupling at the time of the formation of the CMB and the effects on the damping of the baryon-photon fluid. A new and even stronger constraint is presented from the impact on structure formation since tight coupling of baryons to dark matter would inhibit growth of dark matter overdensities that seed dwarf galaxies, in contrast with observation. - Optical Phonon R&D or What Condensed Matter Theory/Computation Can do For You – Sinead Griffin (LBNL) – Slides
Highlights some recent results in condensed matter theory for identifying candidate materials with desirable properties for dark matter scattering. Example are given of polar materials with large Born effective charges and small atomic masses, which are suitable for production of optical phonons from DM-nucleus scattering. - Condensed Matter Systems of Interest – Lucas Wagner (UIUC) – Slides
Highlights more recent results in condensed matter theory for identifying candidate materials with desirable properties for dark matter scattering. Examples of low-gap materials relevant for DM-electron scattering are discussed, as well as the condensed matter quantities most relevant for DM-electron scattering, specifically the dielectric function, which better characterizes the properties of real materials than a band structure model.