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Events on Wednesday, May 3rd, 2023

Preliminary Exam
Multi-Messenger Searches for High Energy Cosmic Ray Accelerators
Time: 11:00 am - 1:00 am
Place: 4274 Chamberlin
Speaker: David Guevel, Physics Graduate Student
Abstract: The sources of the highest energy cosmic rays are unknown. Within the Milky Way, cosmic rays, which are high energy protons and nuclei, are accelerated to a few PeV by accelerators which have yet to be identified. Even higher energy cosmic rays are thought to be accelerated by distant active galaxies. In both cases, cosmic rays themselves cannot be directly traced back to their sources because they are deflected by the magnetic fields they traverse. Multi-messenger observations can reveal the origin of the cosmic rays through the underlying physics that connects cosmic rays, gamma-rays, and neutrinos. I will present two ongoing works: (1) X-ray observations by Swift-XRT of the Cygnus Cocoon, a gamma-ray source which has been identified as a likely PeV cosmic ray source within the Milky Way, can be used to rule out alternative models of gamma-ray emission thus providing evidence the cosmic ray acceleration model. (2) IceCube neutrinos are an indicator of high energy cosmic ray production. A cross correlation of IceCube neutrinos with a galaxy catalog can constrain the sources that emit extragalactic cosmic rays.
Host: Ke Fang
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Theory Seminar (High Energy/Cosmology)
Building non-vanilla QCD axion models
Time: 1:00 pm - 2:30 pm
Place: Chamberlin 5280
Speaker: Felix Yu, Fermilab
Abstract: In [1] and [2], my co-authors and I revisit the the field theory of axion model building from two separate perspectives. We first considered [1] the effects of small-size instantons arising from enlarged color gauge groups on the QCD axion mass, reaffirming earlier results that QCD axion masses can be parametrically heavier than vanilla models when the confinement effects of the extended color group symmetry contribute to the Peccei-Quinn (PQ) breaking. Notably, we discuss an improvement of the vanilla chiral Lagrangian that readily incorporates non-vanilla 't Hooft determinantal operators. In [2], we present the "Anarchic Axion" model where a possible soft-breaking of PQ symmetry is included in the scalar potential. Depending on the phase and magnitude of the soft-breaking term, an arbitrarily light QCD axion remains to solve the strong CP problem, albeit at the expense of increasing fine tuning. Besides expanding the axion parameter space beyond the vanilla QCD axion band, we have also discussed the phenomenology of axion-like particle effective field theories when the Standard Model is extended to include a gauged baryon number symmetry, offering new collider signatures for ALPs and Z' bosons [3]. [1] Kivel, Laux, FY, [JHEP 11(2022) 088, arXiv:2207.08740] [2] Elahi, Elor, Kivel, Laux, Najjari, FY [arXiv:2301.08760] [3] Kivel, Laux, FY [JHEP 03 (2023) 078, arXiv:2211.12155]
Host: George Wojcik
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Astronomy Colloquium
Building stars, planets and the ingredients for life in space
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Ewine F. van Dishoeck, Leiden Observatory, Leiden University, the Netherlands
Abstract: Thousands of planets have been discovered around stars other than our
Sun. But how and where are these exo-planets born, and why are they so
different from those in our own solar system? Which ingredients are
available to build them? Thanks to powerful new telescopes, including
the James Webb Space Telescope, astronomers can now zoom in to
planetary construction sites and study their composition. Water and a
surprisingly rich variety of organic materials are found near forming
stars, including simple sugars, ethers, alcohols and hydrocarbons.
How are these molecules made under the extreme conditions in space and
can they be delivered to new planets to form the basis for life
elsewhere in the universe?
Host: Ke Zhang
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