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
- bkoebbe@illinois.edu
- Views
- 238
- 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.