Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. HET Brown Bag Seminar | Modular forms and zeta-values in string amplitudes (November 9, 2021 11:30am) https://events.umich.edu/event/88953 88953-21659252@events.umich.edu Event Begins: Tuesday, November 9, 2021 11:30am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Several rich mathematical objects appear in superstring scattering amplitudes, such as modular graph forms and Riemann zeta-values. Modular graph forms are modular forms associated with vacuum Feynman graphs. Both modular graph forms and zeta-values admit a grading by their transcendental weight. I shall review the transcendental structure of superstring amplitudes, including the conjectured uniform transcendentality of genus-one amplitudes in Type II superstring theory. I shall also describe recent work with Eric D’Hoker (arXiv:2110.06237) in which we evaluated the integrals of several infinite families of modular graph functions over genus-one moduli space.

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Lecture / Discussion Thu, 04 Nov 2021 05:10:02 -0400 2021-11-09T11:30:00-05:00 2021-11-09T12:30:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | A Mirror Dark Sector and the Hubble Tension (March 9, 2022 12:00pm) https://events.umich.edu/event/92970 92970-21698560@events.umich.edu Event Begins: Wednesday, March 9, 2022 12:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

The inference of the present expansion rate from the Cosmic Microwave Background (CMB) and other early-time probes (assuming standard cosmology) is in significant tension with several direct measurements of the same quantity. If this discrepancy is not due to unresolved systematics, it could provide strong evidence for physics beyond the standard models (SM) of particle physics and cosmology. In a recent work Cyr-Racine, Ge and Knox pointed out a strong degeneracy in the evolution equations describing the CMB that, under certain strong assumptions, enables one to resolve the tension. A physical implementation of this degeneracy requires the introduction of a hidden sector with several puzzling features: 1) low-energy field content that is nearly identical to the SM, 2) similar energy density ratios between different components as in the visible sector and 3) recombination of dark states that is simultaneous with standard hydrogen recombination. I will describe a model based on a partial copy of the SM with asymmetric reheating where these features arise naturally. Both our model and the original proposal of Cyr-Racine, Ge and Knox require a significantly lower helium fraction than is directly observed in the late universe. Thus, the Hubble tension is shifted to a helium one

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Lecture / Discussion Thu, 03 Mar 2022 14:44:34 -0500 2022-03-09T12:00:00-05:00 2022-03-09T13:00:00-05:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion