Events at Physics |
Events During the Week of November 16th through November 22nd, 2025
Monday, November 17th, 2025
- Theory Seminar (High Energy/Cosmology)
- What is the QCD axion mass?
- Time: 1:00 pm - 2:30 pm
- Place: Chamberlin 5280
- Speaker: Joshua N. Benabou, UC, Berkeley
- Abstract: The QCD axion may solve the strong CP problem and constitute the dark matter (DM) abundance in our Universe. Peccei-Quinn (PQ) axions may form axion strings if the PQ phase transition occurs after inflation. I will discuss recent advances in the computation of the QCD axion DM mass in this scenario from the most precise and accurate lattice simulations to-date of axion-string networks, leading to a predicted mass range of 40 - 300 µeV. On the other hand, string theory axions, which are compelling solutions to the PQ quality problem, do not generically form strings - except in special inflationary paradigms such as brane inflation - meaning that there is no unique predicted value for the QCD axion DM mass. Nonetheless, if a Grand Unified Theory is assumed, I will explain why in broad regions of the string landscape, the mass of a stringy QCD axion is expected to be ~ 0.01 to 10 neV, independently of its DM fraction.
- Host: Joshua Foster
Tuesday, November 18th, 2025
- No events scheduled
Wednesday, November 19th, 2025
- Preliminary Exam
- Searches for High-energy Neutrinos Accompanying Astrophysical Transients
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin Hall Room 5310
- Speaker: Alicia Mand
- Abstract: Multi-messenger astronomy enables us to probe extreme astrophysical phenomena in new ways. In particular, astrophysical neutrinos reveal information that is not available via any other messenger. Neutrinos are the “smoking gun” signature for hadronic processes – meaning that identification of neutrino sources can elucidate the origins of high-energy cosmic rays. Multiple observatories, such as the IceCube Neutrino Observatory and KM3NeT, are currently collecting data on astrophysical neutrinos. The first detection of high-energy astrophysical neutrinos was reported in 2013 by the IceCube collaboration. However, despite detecting astrophysical neutrinos for over a decade, the sources of these neutrinos are still largely unknown, despite thorough searches. I will present results and work in progress from three such searches using data from the IceCube Neutrino Observatory. The first is a search for neutrinos from SN 2023ixf, the closest and brightest core-collapse supernova in the last decade. The second is a follow-up of the highest-energy neutrino ever detected, measured by KM3NeT to have energy approximately 200 PeV, to search for additional neutrinos from the same direction that could help determine its origin. Finally, I will present a search under development for neutrinos in the directions of fast radio bursts (FRBs) detected by the CHIME telescope.
- Host: Justin Vandenbroucke
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Higgs boson pair production
- Time: 12:00 pm - 1:00 pm
- Place: 5280 Chamberlin & Zoom:
- Speaker: Irene Dutta, Fermilab
- Host: Sridhara Dasu
Thursday, November 20th, 2025
- R. G. Herb Condensed Matter Seminar
- Disorder-induced fractionalization of pair density waves
- Time: 10:00 am - 6:00 pm
- Place: 5310 Chamberlin
- Speaker: Julian May-Mann, Stanford University
- Abstract: Pair-density waves (PDWs) are unconventional superconductors in which the order parameter periodically oscillates in space. Compared to other superconductors, PDWs are particularly susceptible to disorder, since random impurities can disrupt the periodic structure that defines them. However, it is not clear whether disorder completely destroys the PDW or instead gives rise to a new phase. Here, we show that a new phase can indeed arise, by considering a strongly inhomogeneous limit in which the system consists of a random collection of PDW puddles embedded in a metallic background*. When the puddles are dilute, they become phase coherent at low temperatures, resulting in a state that is macroscopically equivalent to an s-wave superconductor. This can be viewed as an example of order-parameter fractionalization, in which the PDW order splits into an s-wave superconducting component and a charge-density-wave component, the latter of which is destroyed by disorder. This result highlights the unexpected robustness of superconductivity in PDWs and provides new insights into the effects of disorder on d-wave superconductors.
- Astronomy Colloquium
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: TBD, TBD
- Host: Nicholas Stone
Friday, November 21st, 2025
- Preliminary Exam
- Measuring the Flavor Composition of the Cosmic Neutrino Flux at High Energies with IceCube
- Time: 10:00 am - 12:00 pm
- Place: Chamberlin Hall Room 5280
- Speaker: Hannah Erpenbeck
- Abstract: The IceCube Neutrino Observatory detects neutrinos by instrumenting 1 km3 of deep glacial ice with photomultiplier tubes. These detections allow for the study of possible astrophysical neutrino sources and the measurement of the diffuse astrophysical neutrino flux. The flavor composition of the measured flux is a very important component in understanding and modeling the astrophysical neutrino flux. In addition, an improved measurement of the flavor composition of the astrophysical neutrino flux at Earth allows us to infer the flavor composition at the sources and thus provides insights into neutrino production mechanisms. I will present the plan for a new flavor analysis using a combination of datasets used within the IceCube Collaboration. Previous flavor measurements with IceCube focused on individual samples targeting distinct event types, mostly dominated by events with interaction vertices inside the detector. Building on existing efforts, I plan to perform such a measurement on an expanded dataset. Such a sample includes contained and uncontained events, incorporates improved ice modeling, and achieves the highest statistics for the high-energy neutrino flux. These updates in event classification promise improvement in the sensitivity of the flavor measurement. Identifying double-cascades among tracks and cascades is a continuous effort, and the main focus of my talk.
- Host: Albrecht Karle
- Physics Department Colloquium
- Have we observed neutron star rockets?
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241
- Speaker: Yuri Levin, Columbia University
- Abstract: Neutron stars are incredible playgrounds for theoretical physicists and observational astrophysicists, featuring the most intense concentrations of all four known force-fields of nature. In this talk, I will highlight a peculiar effect that leads to a prediction of an electromagnetic rocket force. I will explain how recent Gaia observations allow us to probe this force. I will show an exact computation of the rocket force in Force-Free Electrodynamics, which is a good theory describing magnetospheres of many, but not all neutron stars (no knowledge of plasma physics will be assumed). Gaia's neutron stars may well have to be described by a different theory.
- Host: Vladimir Zhdankin