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David Jacobs (Norwich University)

Date: Tue. October 26th, 2021, 11:30 am-12:30 pm
Location: Foldy room

What can effective quantum mechanics do for you?

In this talk I will explain how a stubborn curiosity about boundary conditions in quantum mechanics led to the development of a long-distance effective approach to describing quantum mechanical systems, borrowing heavily from the ideas of effective field theory. I will describe how this approach is applied to yield an effective (quantum defect) theory of positronium. This is pertinent because of a recent 4.2 σ discrepancy between the theory of bound-state quantum electrodynamics (QED) and a recent transition frequency measurement by Gurung et al. (2020 & 2021). The effective theory that I will discuss not only provides an accurate and economical means to fit the positronium spectrum, but also reveals some hitherto unknown (and non-trivial!) relationships that exist within bound-state QED. The effective approach that I will present likely has extensions to other hydrogenic systems and would provide a useful complement to bound-state QED, but it may also be of use in other domains of physics, such as condensed matter and hadronic physics.

During the talk I will give some of the details of how “the sausage was made”, highlighting early work that I did with Scott Beck and Harsh Mathur during my grad school days at Case, some of the ups and downs of doing theoretical physics, as well as what it was like to leave — and then return to — academia.

Host: Kurt Hinterbichler
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