Research Seminars @ Illinois

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Tailored for undergraduate researchers, this calendar is a curated list of research seminars at the University of Illinois. Explore the diverse world of research and expand your knowledge through engaging sessions designed to inspire and enlighten.

To have your events added or removed from this calendar, please contact OUR at ugresearch@illinois.edu

High Energy Physics Seminar - Qianshu Lu (IAS) "The Quality/Cosmology Tension for a Post-Inflation QCD Axion"

Event Type: Seminar/Symposium
Sponsor: Physics Department
Location: 464 Loomis
Date: Apr 11, 2025 11:00 am
Speaker: Qianshu Lu (IAS)
Contact: Brandy Koebbe
E-Mail: bkoebbe@illinois.edu
Views: 17
Originating Calendar: Physics - High Energy Physics Seminar; The QCD axion is not only a leading contender as a solution to the Strong CP problem, it is also a natural dark matter candidate. In particular, the post-inflationary axion is particularly attractive because of the possibility of a unique prediction of the axion mass if axion makes up all of dark matter. On the other hand, QCD axion models often suffers from the so-called axion quality problem, where the axion shift symmetry is unprotected from quantum gravity effects. In this talk I will discuss the tension between solutions to the quality problem and viable cosmology for post-inflationary QCD axions. I will start with a simple Z_N symmetry as an illustrative example of the close connection between the quality problem and the domain wall problem. I will then analyze proposals in the literature that involve more complex symmetry structure and show that they share a set of cosmological issues. Our study suggests that a viable post-inflationary QCD axion model is likely to have a non-standard cosmological history which could significantly impact the prediction of the "correct" axion mass.

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