Graduate Program Events |
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
- Subatomic to Supernova: Two unrelated tales of neutrinos and dark matter
- Time: 12:30 pm - 6:00 pm
- Place: 2314 Chamberlin
- Speaker: Daniel Heimsoth, Physics PhD Graduate Student
- Abstract: I will present my work on two recent papers. First, supernovae expel a large fraction of their energy in neutrinos, making them a potentially useful detection channel to understand properties of stellar core collapse. With the construction of new, larger neutrino experiments such as Hyper-Kamiokande, DUNE, and IceCube Gen2 in the near future, we will have the capability to measure the time-dependent neutrino flux from nearby core-collapse supernovae. I will show how using the neutrino signal from a theorized hadron-quark phase transition during core collapse can allow us to not only triangulate the position of the supernova in the sky to good precision but also set limits on the absolute neutrino mass scale.
Turning our attention from neutrinos to dark matter, I will then describe my work on quantifying uncertainties in direct detection dark matter experiments stemming from uncertainties in nuclear modeling. As these experiments shift from considering only the spin-independent and spin-dependent operators to a complete set of operators coupling dark matter to nuclei, it becomes especially important to understand all sources of uncertainty. I will explain how we calculated the nuclear model uncertainties for xenon, a common choice of target in direct detection experiments, and how these uncertainties can be significantly large for certain operators. - Host: Baha Balantekin
- 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
- Last Fall Semester class day
- Abstract: *Note: actual end time may vary.* URL:
- 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
- A Search for Vector-Like Leptons (VLLs)
- Time: 2:30 pm - 4:30 pm
- Place: 4272 Chamberlin
- Speaker: Elise Chavez, Physics PhD Graduate Student
- Abstract: The Standard Model is the current theoretical description of fundamental particles and their interactions. While it is able to describe the majority of phenomena that we observe, there are many that it cannot accommodate for. Such phenomena are dark matter, dark energy, and lepton non-universality. New theories have been proposed that extend the Standard Model in order to answer these long standing questions. One such extension is the 4321 model that predicts several new particles, one of which is the vector-like lepton (VLL). A search for pair produced vector-like leptons (VLLs) is proposed using the Run II data that was produced by proton-proton collisions at sqrt(s) = 13 TeV and collected by the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC). In this search, the modes where the decays of the VLLs result in two Standard Model leptons are examined. This search employs a set of optimized kinematic selection criteria to enhance the signal, with respect to the Standard Model background, and a data based approach to determine the dominant ttbar background process. The goal of this search is to determine whether we see an excess of events in our data and set limits on the cross section of the VLL pair production.
- Host: Tulika Bose
- Investigation of oxide defects and heterostructure modifications for use in quantum computing
- Time: 3:30 pm - 5:30 pm
- Place: B343 Sterling
- Speaker: Emily Joseph, Physics PhD Graduate Student
- Abstract: Si/SiGe quantum dots are attractive candidates for quantum computation yet there are significant challenges to overcome in an effort to improve the scalability of the system. These devices are susceptible to charge noise, some of which may arise from two-level systems (TLS) in the oxide. In this work we use resonator measurement and STEM images to investigate ALD oxide quality to improve semiconducting qubits. Another challenge inherent to Si/SiGe quantum dots is the energy splitting of the conduction band valley states. The valley splitting in Si devices is largely variable and unpredictable and it would be advantageous to be able to predictably rely on a designed-in valley splitting. A modification to the heterostructure has been produced with oscillating concentration of Ge through the quantum well, called the Wiggle Well. Theory predicts that this structure will show strong spin-orbit coupling and with shear strain can have a deterministically large valley splitting. Here we describe methods for mechanically introducing shear strain into the quantum well and a proposed experiment measuring the spin-orbit coupling of the Wiggle Well and making a Loss-DiVincenzo qubit without a micromagnet.
- Host: Mark Eriksson
Thursday, December 14th, 2023
- Study day
- Abstract: *Note: actual end time may vary.* URL:
Friday, December 15th, 2023
- Exams
- Abstract: *Note: actual end time may vary.* URL:
Saturday, December 16th, 2023
- Exams
- Abstract: *Note: actual end time may vary.* URL:
Sunday, December 17th, 2023
- Commencement
- Time: 10:00 am - 11:00 am
- Abstract: URL: