CCAPP Fellows Symposium 2025

12:00 pm -- Poster session & Lunch 

1:00 pm -- Welcome by Dr. John Beacom

1:05 pm -- Astroparticle I

Rasmi Hajjar: "Using Natural Neutrinos to Probe Nature Properties"

Justin Flaherty: "The Askaryan Radio Array: Challenges in Polarization Reconstruction"

Alisa Nozdrina: "Towards the Radio Detection of Cosmic Rays with the Radio Neutrino Observatory in Greenland"

2:05 pm -- Astronomy I

Manami Roy: "Cosmic Rays: The Hidden Architects of the Circumgalactic Medium"

Raquel Forés Toribio: "ASASSN-24fw in the context of long and deep stellar dimmings in time-domain surveys"

Lucy Lu: "Spectroscopic Follow-up of Young High-α Dwarf Star Candidates: Still Likely Genuinely Young"

3:05 pm -- Break

3:20 pm -- Cosmology I

Misha Rashkovetskyi: "Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect"

Molly Wolfson: "Measuring the 1D Lyman-α forest power at z > 5"

Naim Göksel Karaçaylı: "Small-scale cosmology with DESI Lyman-alpha forest"

4:20 pm -- Closing & Group Photo

12:00 pm – Poster session & Lunch

1:00 pm – Welcome from Dr. John Beacom

1:05 pm -- Cosmology II

Xinyi Chen: "Strengthening the primordial non-Gaussianity constraints from high-order statistics by reconstructing the density field"

Charuhas Shiveshwarkar: "Non-Universality and Assembly bias in the hunt for Local Primordial non-Gaussianity"

Peter Taylor: "Unlocking Nonlinear Structure Growth Across Dark Energy Model Space with Neural ODEs"

2:05 pm -- Astronomy II

Michael Tucker: "The First Data Release of the Spectroscopic Classification of Astronomical Transients survey"

Jung-Tsung Li: "Flux expulsion, homogenization, and the gamma-ray emission from the Sun"

Milan Pesta: "Toward the Detection of Massive Dark Companions in Photometric Surveys Using Gaussian Process Regression and Principal Component Analysis"

3:05 pm -- Break

3:20 pm -- Astroparticle II

William Luszczak: "Physics 5700 Near the Base of a Forming EF-3 Tornado"

Paramita Dasgupta: "ARA at the South Pole: Searching for the Highest-Energy Neutrinos"

Lucas Beaufore: "Design and Integration of The Payload for Ultrahigh Energy Observations (PUEO)"

4:20 pm -- Closing & Group Photo

Presenter: Rasmi Hajjar (online) 

Title: Using Natural Neutrinos to Probe Nature Properties 
Abstract: In this talk I will summarize different physical properties that we can probe using non-human generated neutrino fluxes across all the energy range. I will focus on cosmological, supernovae, atmospheric, and Ultra-High-Energy neutrinos and highlight the potential they might have in determining different quantities related to neutrino masses, oscillation parameters, the density of the Earth and properties of Heavy Dark Matter. This aims to highlight the relevance and power of non-human neutrinos and emphasize the importance of the proper characterization and understanding of natural neutrino fluxes. 

Presenter: Justin Flaherty 

Title: The Askaryan Radio Array: Challenges in Polarization Reconstruction 
Abstract: The Askaryan Radio Array (ARA) is an ultra-high energy (> 10 PeV) neutrino detector located in Antarctica at the geographic South Pole. It consists of five in-ice stations of antennas that are designed to detect Askaryan Radiation, coherent radio emission generated by relativistic particle showers that are byproducts of neutrino interactions in dense dielectric media. Understanding the polarization of these signals is a critical step for determining neutrino trajectories and identifying their astrophysical origins. Observations from field calibrations with radio pulsers have shown unexpected effects on polarization as the signal propagates through the ice, such as rotations in the vector or time-delays between vector components, which present challenges in reconstruction. This talk will give an overview of these challenges and the efforts being made to address them. 

Presenter: Alisa Nozdrina 

Title: Towards the Radio Detection of Cosmic Rays with the Radio Neutrino Observatory in Greenland 
Abstract: The Radio Neutrino Observatory in Greenland (RNO-G) is a particle detector designed to search for ultra-high-energy neutrinos. Located atop the world’s second largest ice sheet, RNO-G is also sensitive to radio signals from particle showers generated by cosmic rays, which are a significant and challenging background to isolate. Yet detecting these cosmic rays would mark the first observation of Askaryan radiation in natural ice and serve as a crucial validation of the radio detection technique. This talk will present recent progress in identifying cosmic ray signatures within the RNO-G dataset. 

Presenter: Manami Roy 

Title: Cosmic Rays: The Hidden Architects of the Circumgalactic Medium 
Abstract: Cosmic rays (CRs) remain a key uncertainty in galaxy evolution due to their poorly constrained transport and acceleration in diverse plasma environments. They may play a crucial role in shaping the multiphase structure of the Circumgalactic Medium (CGM), with their impact varying across different phases depending on their transport properties and coupling with the thermal plasma. A central question is how CRs might affect different CGM phases and whether CR pressure support may be dynamically significant. In this talk, I will present results from a suite of idealized simulations of a Milky Way-type host galaxy with varying satellite distributions, incorporating CRs from supernovae into both the host and satellite galaxies. I find that CR pressure enhances the surface area of ram pressure-stripped cool satellite clouds, boosting cooling in turbulent mixing layers and thereby prolonging cloud survival and increasing the cold-phase covering fraction. I will also present results from new simulations exploring the dynamics of CR-driven shells and super-bubbles on various scales in and around star-forming galaxies. Overall, these findings highlight the potential importance of CRs on galaxy ecosystems and how uncertainties in CR transport properties map to uncertainties in their importance. 

Presenter: Raquel Forés Toribio 

Title: ASASSN-24fw in the context of long and deep stellar dimmings in time-domain surveys 
Abstract: ASASSN-24fw is a 13th-magnitude star that underwent a 4.12 mag fading in the g band for 8 months, from September 2024 to late May 2025. The optical eclipse is nearly achromatic, although slightly deeper in bluer filters, and the V band emission is polarized by up to 4%. The event is consistent with obscuration by a dusty disk, either a protoplanetary or an evolved debris disk, composed of large (~20 μm) carbonaceous or water-ice grains precessing around the star. Combining this recent dimming with DASCH archival photometry from 1894 to 1989, a 43.8-year period seems likely, highlighting the importance of long-term photometric surveys. To contextualize this event, we conduct a survey of long and deep occultation events, finding 42 additional systems, of which 7 were discovered by the ASAS-SN survey. While the full sample is widely distributed in an optical color-magnitude diagram, roughly half show mid-infrared excesses. It is likely that many of the others have cooler dust, since it seems essential to produce the events. Classical archetypes of long and deep stellar eclipses (ε Aurigae and KH 15D) do not fully capture the diversity of scenarios driving these dimmings. Increasing searches for long and deep dimming events will also help to assess whether there are features common to all systems and to systematically categorize them. 

Presenter: Lucy Lu 

Title: Spectroscopic Follow-up of Young High-α Dwarf Star Candidates: Still Likely Genuinely Young 
Abstract: The question of whether genuinely young high-α stars exist has been discussed for over a decade since their discovery from asteroseismology of giant stars. Young high-α stars are hard to explain with traditional chemical evolution model as the high-α disk is associated with high star formation efficiency, associated with the early epoch of star formation in the Milky Way. Most subsequent studies since then have focused on evolved stars as the sample size is large, and ages are easier to determine. However, it is challenging to break the degeneracy between the binary interaction and the genuinely young scenarios, as mass transfer can rejuvenate stars and make them appear more massive than they were. Luckily, lithium can serve as an unambiguous indicator for identifying merger products in dwarfs thanks to its low burning temperature. Combined with recent advances of gyrochronology, we are now able to identify young high-α dwarf stars through rotation, and degeneracy between the mass transfer and genuinely young scenarios can be finally broken using lithium measurements. We performed high-resolution spectroscopic follow-up of young high-α dwarf candidates identified in a previous study using Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), and confirm 3 additional stars that are most likely genuinely young. I will talk about their common properties and likely formation pathways in my talk. 

Presenter: Misha Rashkovetskyi 

Title: Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect 
Abstract: The thermal Sunyaev-Zeldovich (tSZ) effect is associated with galaxy clusters — extremely large and dense structures tracing the dark matter with a higher bias than isolated galaxies. We propose to use the tSZ data to separate galaxies from redshift surveys into distinct subpopulations corresponding to different densities and biases independently of the redshift survey systematics. Leveraging the information from different environments, as in density-split and density-marked clustering, is known to tighten the constraints on cosmological parameters like $\Omega_m$, $S_8$ and neutrino mass. By focusing on higher detection levels, we expect to better constrain the halo and galaxy formation processes, e.g., assembly bias effects. By restricting to the low detection levels, we hope to remove the larger non-linearities challenging for theoretical modeling, and better constrain modified gravity. We use the overlap between the footprints of the Dark Energy Spectroscopic Instrument (DESI) and the Atacama Cosmology Telescope (ACT). We discover a significant increase in the large-scale clustering of DESI luminous red galaxies (LRGs) corresponding to pixels in the ACT DR6 + Planck tSZ y map with 1-4 sigma detections, below the cluster candidate threshold. We also find that such galaxies have higher line-of-sight coordinate (and velocity) dispersions and a higher number of close neighbors. Thus, we show that there is valuable cosmological information in the thermal Sunyaev-Zeldovich map in the "noise" beyond the individual cluster candidates. 

Presenter: Molly Wolfson 

Title: Measuring the 1D Lyman-α forest power at z > 5 
Abstract: Some of the most important open questions in cosmology are how and when the intergalactic medium (IGM) was reionized by the first luminous sources. Reionization is thought to be complete by redshift z~5, though the thermal and ionization imprints of this epoch may persist at lower redshifts. As ionization fronts propagate during reionization, they heat the IGM and generate temperature fluctuations that deviate from a simple power-law temperature-density relation. At the same time, the ultraviolet background (UVB) evolves rapidly due to the growth and merging of ionized bubbles, and exhibits spatial fluctuations prior to their overlap. Both temperature fluctuations and UVB inhomogeneities leave characteristic signatures in the Lyman-α (Lyα) forest. I will discuss measuring the one-dimensional Lyα forest flux power spectrum at large scales, where fluctuations from the IGM’s thermal state and UVB inhomogeneities are expected to contribute. I will present recent progress in quantifying possible excess power at these scales and discuss implications for constraining the timing and nature of reionization-era processes. 

Presenter: Naim Göksel Karaçaylı 

Title: Small-scale cosmology with DESI Lyman-alpha forest 
Abstract: The Lyman-alpha forest enables the study of cosmic structure on scales much smaller than those probed by baryon acoustic oscillations (BAO). While the BAO feature appears at 150 Mpc, the Lyman-alpha forest can resolve structure down to 1 Mpc, limited primarily by spectrograph resolution. This sensitivity makes it a powerful probe of small-scale clustering, which is influenced by the mass of neutrinos and hypothetical dark matter particles. However, this advantage comes with a requirement for a careful study of instrumental systematics. We quantify the small-scale clustering using the one-dimensional flux power spectrum (P1D). In this talk, I will present our P1D measurements from DESI Data Release 1 and outline our strategy for mitigating systematics related to CCD defects. By the time of the symposium, I expect to share preliminary cosmological insights from this analysis. 

Presenter: Xinyi Chen 

Title: Strengthening the primordial non-Gaussianity constraints from high-order statistics by reconstructing the density field 
Abstract: Inflation remains one of the enigmas in fundamental physics. The bispectrum contains valuable information to extract primordial non-Gaussianity signals that help discern different inflationary models. For the local primordial non-Gaussianity, adding the bispectrum to the power spectrum provides more constraining power; for the non-local types, the bispectrum is more necessary, since the power spectrum does not show sizeable signals. However, the full bispectrum is computationally expensive. I will introduce a quadratic estimator that can fully capture the bispectrum information in the quasi-linear regime, but with a computational cost at the level of two-point statistics. I will then introduce a reconstruction procedure on top of the quadratic estimator that allows us to extract more signals from the bispectrum, thus offering more stringent constraints on both the local and non-local types of primordial non-Gaussianities. 

Presenter: Charuhas Shiveshwarka 

Title: Non-Universality and Assembly bias in the hunt for Local Primordial non-Gaussianity 
Abstract: Local Primordial non-Gaussianity (LPnG) is an important observational target for current and upcoming large-scale galaxy surveys. A detection of LPnG would conclusively rule out single-field models of inflation and thus significantly constrain the space of possible inflationary models. However, constraints on LPnG obtained from galaxy power spectra are limited by the perfect degeneracy between the LPnG parameter fNL and the bias parameter bϕ – a model relating bϕ to the galaxy/halo bias is therefore needed to obtain any useful constraints on fNL from galaxy power spectra. The relation between bϕ and the galaxy/halo bias is in general poorly understood and can differ significantly from the universal mass function ansatz. In this talk, I shall describe recent work investigating this non-universality in the context of dark-matter halos using the Separate Universe framework, focussing on dark-matter halos selected by mass and/or concentration. Our work shows how the Separate Universe framework can provide a natural explanation for the universality (as well as deviations thereof) observed in the clustering of dark-matter halos. 

Presenter: Peter Taylor 

Title: Unlocking Nonlinear Structure Growth Across Dark Energy Model Space with Neural ODEs 
Abstract: The recent DESI DR2 results suggest the dark energy equation of state is evolving with time. If true, by measuring the growth of structure as well as the background expansion of the Universe, this decade’s leading photometric surveys – Euclid, Rubin and Roman – have the potential to independently confirm this result and distinguish between dark energy models. However, to realize this potential we must first be able to model the nonlinear growth of structure across the entire dynamical dark energy landscape. I show how this can be achieved using neural ordinary differential equations. 

Presenter: Michael Tucker 

Title: The First Data Release of the Spectroscopic Classification of Astronomical Transients survey 
Abstract: The Universe is filled with the eruptive and explosive, encompassing everything from exploding stars (supernovae) to stars shredded by supermassive black holes (tidal disruption events). I co-founded the SCAT survey in 2018 to identify exotic and unique transients discovered by the world’s sky surveys, and after several years of successful operations (and 30 papers!), it is time for our first major data release. The final data products include over a thousand spectra of hundreds of transients, spanning supernovae of all types, changing-look/highly variable AGN and quasars, stellar flares, tidal disruption events, and more. We also estimate the time of explosion/first light for each event using publicly available photometry from ongoing surveys such as ASAS-SN and ZTF, with most events having sub-day precision. This large collection of spectrophotometry will benchmark current and next-generation state-of-the-art multi-dimensional models with an emphasis on viewing-angle and asymmetry effects. 

Presenter: Jung-Tsung Li 

Title: Flux expulsion, homogenization, and the gamma-ray emission from the Sun 
Abstract: The solar disk is a continuous source of GeV--TeV gamma rays. The emission is thought to originate from hadronic Galactic cosmic rays (GCRs) interacting with the gas in the photosphere and uppermost convection zone after being reflected by solar magnetic fields. Despite this general understanding, existing theoretical models have yet to match the observational data. At the photosphere and the uppermost convection zone, granular convection drives a multi-scale magnetic field, forming a larger-scale filamentary structure while also generating turbulence-scale Alfven wave turbulence. In this talk, I will show that the larger-scale filamentary field shapes the overall gamma-ray emission spectrum, while the Alfven wave turbulence is critical for further suppressing the gamma-ray emission spectrum below 100 GeV. In a standard Alfven wave turbulence level, our model's predicted spectrum slope from 1 GeV to 1 TeV is in excellent agreement with observations from Fermi-LAT and HAWC. The key contribution of this study is providing a new theoretical framework for using solar disk gamma-ray observations to probe hadronic GCR transport in the lower solar atmosphere. 

Presenter: Milan Pesta 

Title: Toward the Detection of Massive Dark Companions in Photometric Surveys Using Gaussian Process Regression and Principal Component Analysis 
Abstract: The detection of electromagnetically silent black holes and neutron stars in binary systems through photometric surveys represents a crucial challenge in modern astronomy. These massive dark companions induce ellipsoidal variations in the light curves of their stellar companions, providing a unique opportunity for their detection and characterization. However, these variations are subtle and can easily be obscured by instrumental noise and systematic effects such as stellar spots. In this talk, I will present a novel approach for the detection of dark companion binaries in photometric surveys using Gaussian process regression and principal component analysis. 

Presenter: William Luszczak 

Title: Physics 5700 Near the Base of a Forming EF-3 Tornado 
Abstract: Tornadoes and other severe weather hazards affect thousands of people every year. Despite this, the details surrounding tornadic processes including formation, decay, and longevity are not well understood, partially due to limitations of available instrumentation. Measurements of atmospheric pressure within tornadic systems currently rely almost entirely on in-situ instrumentation, and no existing techniques can provide two-dimensional spatial information of the atmospheric density field. Atmospheric muons may hold a solution to this problem: muons are attenuated by matter, and tornadic storms are large regions of low atmospheric density, suggesting that tornadic storms induce a directional perturbation on the atmospheric muon flux. Measurements of this perturbation could then be used to infer the density field associated with severe weather. This talk will present preliminary results from a pilot field study that measured the atmospheric muon flux near tornadic storms during May 2025, including a measurement of the muon flux near the base of a forming EF-3 tornado. Further applications of this technique (atmospheric muography) to data assimilation-based weather forecasting are also discussed, with potential improvements in forecast accuracy of up to 20% relative to free hydrodynamic model evolution. 

Presenter: Paramita Dasgupta 

Title: ARA at the South Pole: Searching for the Highest-Energy Neutrinos 
Abstract: High-energy particles, such as neutrinos and cosmic rays, offer a unique window into the most extreme astrophysical environments. This talk presents recent efforts to detect these particles using radio techniques. The Askaryan Radio Array (ARA), located at the South Pole, is an in-ice detector designed to detect radio signals from neutrino-induced showers. ARA’s fifth station (A5) features a central phased array that enables low-threshold detection via an interferometric trigger, enhancing sensitivity to low signal-to-noise (SNR) events. I will present the first hybrid ultra-high-energy (UHE) neutrino analysis using A5, combining traditional and phased array data streams with improved event selection and background rejection. ARA is currently analyzing over 500 TB of data collected across all five stations (A1–A5) over the past decade, making it the first radio-based experiment to achieve leading sensitivity to neutrinos up to 1000 EeV. These advancements build on extensive improvements in calibration and simulation, significantly enhancing directional reconstruction and discovery potential. 

Presenter: Lucas Beaufore 

Title: Design and Integration of The Payload for Ultrahigh Energy Observations (PUEO) 
Abstract: The Payload for Ultrahigh Energy Observations (PUEO) is a balloon-borne experiment designed to measure astrophysical and cosmic neutrinos at ultrahigh energy (>1 EeV) with world-leading sensitivities. While in flight, PUEO will monitor the Antarctic ice for impulsive radio signals characteristic of Askaryan radiation produced by neutrino interactions. The PUEO instrument has been successfully integrated at NASA’s Columbia Science Balloon Facility in Texas, and is now preparing to ship to Antarctica for a flight in the austral summer of 2025-2026. This talk will discuss the design and construction of PUEO and its data acquisition system, with a focus on the work done here at OSU. 

Brandon Abrego: "Using QSO LSS Catalogs to Optimize QSO x Lyman Alpha Cross-Correlation Measurements"

Nihar Dalal: "Deciphering Baryonic Feedback in tSZ Galaxy Clusters"

Souradeep Das: "Probing Dark Matter-Standard Model Interactions using JWST Observations of Early Galaxies"

Shea DeFour-Remy: "Generating an Improved Quasar Redshift Catalog with DESI DR2"

Andrew Engel: "Exploring spectroscopic completeness and photo-z performance"

Alan Salcedo Gomez: "First Array-Wide Search for Diffuse UHE Neutrinos with the Askaryan Radio Array"

Spencer Griffith: "Bound States and Sommerfeld Effects in Higgs Coupled Minimal Dark Matter"

Emily Koivu: "Using IGM as a Probe of PBH Dark Matter"

ManHei Leung: "Cosmic ray modulation by the sun"

Youwei Liu: "RNO-G calibration using balloon signal"

Payton Linton: "Probing Subsurface Lunar Structure with Cosmic Ray Shower Emissions"

Charlie Mace: "Constraining Dark Matter with Substructure Lensing"

Alex Machtay: "Probing Subsurface Lunar Ice with Cosmic Ray Showers"

Everett McArthur: "Quasars acting as Strong Lenses Found in DESI DR1"

Obada Nairat: "Improving solar neutrino sensitivity at JUNO"

Cara Nel: "Corrections to Hawking radiation from asteroid-mass primordial black holes: Formalism of the exchange interaction"

Paarmita Pandey: "Explosive Dispersal Outflows as a class of Gamma-ray sources"

Zoe Riesen: "Neutrino Telescopes: Design and Analysis"

Anuvab Sarkar: "Sub GeV Dark Matter Detection using Bilayer Graphene"

Wynne Turner: "Maximizing cosmological information from Lyman-alpha forest correlations"

Jason Yao: "Cross-Correlation & Locating Signal Origin"

Melanie Zaidel: "A Nu Look at the Sun: Probing the conditions of the Solar Core using B-8 Neutrinos"

Chloe Zheng: "Simulating Self-Interacting Dark Matter Halos"