Thesis Defense |
Events During the Week of December 10th through December 17th, 2023
Monday, December 11th, 2023
- Discovery, Demographics, and Dark Matter Implications of Faint Dwarf Galaxies in Wide-area Optical Surveys
- Time: 12:00 pm
- Place: B343 Sterling
- Speaker: Mitch McNanna, Physics PhD Graduate Student
- Abstract: The combined sky coverage and depth of modern wide-area ground-based optical imaging surveys, in particular the Dark Energy Survey, have made possible the discovery and cataloging of the least luminous known galaxies. The demographics of faint dwarf galaxies throughout our local environment and the properties of the smallest individual ultrafaint galaxies have broad implications for astrophysics. I have designed and implemented search algorithms to identify faint dwarf galaxies both within the gravitational influence of the Milky Way and beyond out to the edges of the Local Group. The census of ultrafaint Milky Way satellites has placed competitive constraints on several alternative dark matter models, established the importance of the Large Magellanic Cloud in the formation of our local galactic environment, and increased our understanding of the connection between the smallest galaxies and the dark matter halos that host them. The search for faint field dwarf galaxies beyond the Milky Way uncovered one of the most diffuse dwarf galaxies ever discovered, the largest galaxy known at its luminosity. By comparing the current catalog of nearby dwarf galaxies to the results of searches over simulated versions of the Local Group, I conclude that we have likely exhausted the power of searches for resolved stellar populations in current wide-area sky coverage. Looking forward, this work informs what we might expect to discover in future surveys covering new areas of sky or with deeper data and how these discoveries will change our understanding of the particle properties of dark matter and the nature of galaxy formation.
- Host: Keith Bechtol
Tuesday, December 12th, 2023
- Synthetic Source Injection in The Dark Energy Survey: Measurements of the Survey Transfer Function and Applications to Precision Cosmology
- Time: 2:00 pm - 6:00 pm
- Place: B343 Sterling
- Speaker: Megan Tabbutt, Physics PhD Graduate Student
- Abstract: Presented here is the Dark Energy Survey’s (DES) Synthetic Source Injection (SSI) methodology and applications to precision cosmology for our Y6 analysis of large-scale structure. Our methodology is predicated on injecting models of real objects obtained from our very high signal-to-noise Deep Field observations into our single-epoch wide field images Both of which are critical to the measurements of the three 2-point correlation functions, cosmic shear, galaxy clustering and galaxy-galaxy lensing, from which we constrain cosmological parameters. This methodology was introduced for our Y3 analysis, and was the first example of using SSI to directly calibrate the cosmological measurements from a WF survey. The refinement and expansion of the methodology is presented here. Specifically, we improved our mirroring of the WF image processing pipeline to now fully recreate it. We refactored our code-base to be able to run our SSI at multiple super-computing centers, minimizing wall time and maximizing allocations. We also developed a new injection scheme that injects sources which are preferentially more useful to the cosmological analyses. These as well as other updates, our initial Y6 SSI results, and their applications to precision cosmology will be discussed at length in this thesis. which are then processed identically to the original wide images. Inherent to this methodology, is that the synthetic sources automatically inherit the same systematics of the real wide field data, a highly sought after achievement for many systematics modeling pipelines that is nearly impossible to achieve from forward modeling techniques alone. In the end, we obtain wide field photometry catalogs of the deep field objects including their inheritance of the systematics. These catalogs are a Monte Carlo sampling of the transfer function of the survey and can be used for calibration and diagnostics, as well as aid in the calculation and validation of our 3x2pt analysis and consequentially our measurement of cosmological parameter constraints. Specifically, through the photometric redshift calibration of the weak lensing sources and the magnification bias estimate for the lens galaxy samples.
- Host: Keith Bechtol
Wednesday, December 13th, 2023
- Naturalness Demands an Answer: The Imperative of Natural SUSY at the HL-LHC
- Time: 11:00 am - 1:00 pm
- Place: 5310 CH
- Speaker: Kairui Zhang, Physics PhD Graduate Student
- Abstract: We explore the ramifications of natural supersymmetry (natSUSY) frameworks for upcoming experiments at the high-luminosity Large Hadron Collider (HL-LHC). Specifically, we scrutinize the production and subsequent decay modes of heavy SUSY Higgs bosons, both neutral and charged, as well as stop pairs and electroweakino pairs, within the context of natural SUSY. The study highlights the importance of decay hierarchy and the potential existence of a light higgsino for accurate interpretation of LHC data. A detailed examination reveals that the dominant decay modes of heavy winos to Standard Model bosons—W, Z, or h—alongside light higgsinos with weak-scale masses, emerge as a unique signature of the natural SUSY paradigm. The investigation delineates both the discovery and exclusion limits for these heavy SUSY particles, thereby offering critical insights into the viability and constraints of natural SUSY models in the forthcoming LHC runs.
- Host: Vernon Barger
Thursday, December 14th, 2023
- No events scheduled
Friday, December 15th, 2023
- No events scheduled