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Events on Friday, October 9th, 2020

Graduate Introductory Seminar (Physics 701)
Linking the theory and observation of astroparticles
Time: 12:05 pm - 12:55 pm
Place: BBCollaborate
Speaker: Ke Fang, UW Madison Department of Physics
Host: Sridhara Dasu
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Theory Seminar (High Energy/Cosmology)
Gravitational wave probes of axion-like particles
Time: 2:00 pm - 3:00 pm
Place: For zoom link, sign up at:
Speaker: Ben Stefanek, Mainz Institute for Theoretical Physics
Abstract: Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Such particles, which are viable candidates for dark matter, can also produce a stochastic gravitational wave (GW) background in the early universe. This occurs if the axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. This instability exponentially amplifies vacuum fluctuations of a single dark photon helicity, resulting in a rapidly time-varying, anisotropic energy distribution that sources chiral GWs. We identify the regions of ALP parameter space which may be probed by future GW detectors, including ground- and space-based interferometers and pulsar timing arrays. Interestingly, these experiments have the ability to probe axions from the bottom up, i.e. in the very weakly coupled regime which is otherwise unconstrained. A smoking gun for the model is the completely chiral nature of the GW peak, which could be detected by LISA or Einstein Telescope if the signal amplitude is large.
Host: Lars Aalsma
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Department Coffee Hour
Time: 3:30 pm - 4:30 pm
Abstract: Join us weekly for an informal virtual coffee hour! Catch up with others in the department, tell us how things are going, and impress everyone with your Zoom background skills. Coffee Hour is open to any and all faculty, staff, and students in the department. Sometimes we have a topic, and we'll try to get that topic posted here in advance or sent out by email before each coffee hour.
Host: Department
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